Recent advances in integrated solar cell/supercapacitor devices: Fabrication, strategy and perspectives

Graphical abstract

From the microscopic mechanism of different functional unit materials to the energy conversion and storage mechanism of macroscopic integrated devices, the design of highly efficient and stable integrated SCSD, the law of improving solar energy conversion and storage performance by supercapacitors and solar cell stacks were systematically discussed.

Highlights

• •How to balance the photoelectric conversion process and the storage process is crucial.
• •The structures and preparation methods of various types of integrated SCSD were introduced.
• •The strategies for improving the overall performance of integrated devices were evaluated.

Abstract

Background

Solar cell/supercapacitor integrated devices (SCSD) have made some progress in terms of device structure and electrode materials, but there are still many key challenges in controlling electrode performance and improving the efficiency of integrated devices.

Aim of review

It is necessary to study how to balance the photoelectric conversion process and the storage process. From the microscopic mechanism of different functional unit materials to the mechanism of macroscopic devices, it is essential to conduct in-depth research.

Key scientific concepts of review

Here, the structures and preparation methods of various types of integrated SCSD were introduced. Then, the strategies for improving the overall performance of integrated devices were evaluated. Finally, the key objectives of reducing the cost of materials, increasing the stability and sustainability of devices were highlighted. Better matching of different functional units of devices was also prospected.

Introduction

The efficient capture and use of solar energy are of great importance in solving energy-related problems for sustainable energy utilization and societal sustainability [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. Consequently, solar cells have been the focus of extensive international research. Nevertheless, due to the intermittent sunlight, solar cells can’t continuously output power, which makes it difficult to meet the actual demand of people. The integration of solar cell/supercapacitor devices (SCSD) enables the device to simultaneously store and convert energy. This integration can be accomplished in several ways, including linking supercapacitors and solar cells in parallel, in series, or by combining electrolytes. The integrated system provides efficient energy storage and conversion in a single system and increases the overall energy utilization rate. The integration of supercapacitors and solar cells allows for effective power output management of solar cells and overcomes the fluctuating power generation characteristics of solar cell [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48]. During periods of strong light intensity, solar cells transform energy from the sun into electricity, while during periods of weak light or at night, stored electrical energy can be released by the supercapacitor, which facilitates the quick release of a substantial amount of electrical energy, thereby establishing energy provision from solar cells and offering dependable energy supply. This approach makes it possible to make full use of this natural resource [49], [50], [51], [52], [53], [54], [55]. By combining solar cells and supercapacitors, the supercapacitor can quickly charge using solar energy. This stored electric energy can then be released gradually to increase the capacity (Fig. 1). The integrated devices benefit the widespread application of renewable energy amid growing demand. The integrated SCSD has the ability to reduce energy consumption and emissions, thereby mitigating environmental impacts.

Fig. 1.

The advantages of solar cells and supercapacitors.

This has a favorable effect on attaining the objective of sustainable development, encouraging environmental preservation and alleviating the strain on finite resources. The integrated devices hold significant research importance in energy conversion, storage and sustainable development, and are projected to supply more effective, dependable and environmentally friendly solutions for upcoming energy systems (Fig. 2). As a common electrochemical energy storage device, supercapacitors are usually utilized in combination with solar cells to form an integrated system. Nevertheless, the present integrated SCSDs have high cost of preparation, and complicated device connection, which hinder low-cost industrialization of integrated devices [56], [57], [58], [59], [60], [61], [62], [63], [64], [65], [66], [67], [68], [69], [70], [71], [72], [73]. Consequently, exploring low-cost and efficient fabrication techniques for integrated SCSD holds great scientific importance.

Fig. 2.

The applications of solar cells/Supercapacitor integrated devices.

Current research has made significant progress in preparing various solar cells and electrode materials [74], [75], [76], [77], [78], [79], [80], [81], [82]. However, the study on integrated SCSD is still in its early stages, and the efficiencies remain low. Moreover, further investigation is needed to understand the mechanism of integrated devices and strengthen the comprehensive performance of solar energy utilization. To improve the photovoltaic conversion and energy storage characteristics in a reasonable and scientific manner, a comprehensive discussion on the classification, electrode materials and energy storage mechanisms of integrated devices is necessary (Fig. 3). The structures of photovoltaic integrated devices were meticulously evaluated and systematically summarized. Subsequently, an assessment of challenges of devices was conducted, with feasible solutions suggested to overcome existing problems.

Fig. 3.

Strategies for improving the performance of integrated SCSD.

Solar Cell/supercapacitor integrated devices

These supercapacitors which have different structures can be combined with solar cells to act as energy storage devices [83], [84], [85], [86], [87], [88], [89], [90], [91], [92], [93], [94], [95], [96], [97], [98], [99], [100], [101], [102], [103]. The initial devices are connected and controlled independently via external circuits. However, the traditional assembly of SCSD requires external wires for the cooperative work of photovoltaic energy conversion and storage (Fig. 4a) [104], [105], [106], [107]. This integration method leads to increased additional resistance and higher manufacturing cost [75], [79], [81].

Fig. 4.

(a) Separate and (b) integrated SCSD systems [107]. Reproduced with permission of Elsevier, 2018.

To achieve a tight connection and efficient energy conversion between supercapacitors and solar cells, researchers have aimed at developing new materials and manufacturing technologies. Solar cells and supercapacitors are integrated into a single device, providing multiple benefits, namely, simplification of the system structure, reduction of energy loss and improvement of overall performance (Fig. 4) [74], [108], [109], [110], [111], [112]. Since Miyasaka introduced dual-function monomer devices in 2004, various types of devices have progressed a rapid pace [76], [80], [82], [83], [104], [105], [110], [113]. This device integrates the benefits of solar cells and supercapacitors, resulting in high efficiency, power density, fast charge and discharge capabilities. As a result, it has a wide range of potential applications. Solar cells convert light energy into electrical energy, while supercapacitors can store a large amount of electrical energy. By combining the two, energy can be efficiently converted and stored. The integrated device provides a stable power supply for electronic equipment, improving its performance and stability. Additionally, it has a high-power density, surpassing that of traditional solar cells and supercapacitors. This allows it to quickly provide a large amount of power for equipment in high-demand scenarios. Additionally, this integrated device boasts fast charging and discharging capabilities, making it ideal for devices that require rapid power transfer, such as mobile communication devices and electric vehicles.

Dye-sensitized solar cell/supercapacitor integrated device

The Dye-sensitized solar cells (DSSC) solar cell/supercapacitor integrated device achieves efficient energy conversion and storage by combining DSSC with supercapacitor. The device operates through three main processes: photoelectric conversion, electrochemical energy storage, and energy output. During photoelectric conversion, sunlight is absorbed by the dye in the DSSC’s sensitized layer, resulting in the creation of electron-hole pairs. The electron-hole pairs diffuse and transport in the dye-sensitized layer and are captured by the conductive electrode and the counter electrode respectively, forming a current. Additionally, electrochemical energy storage occurs when the electrons generated in the photoelectric conversion process flow through the conductive electrode and enter the supercapacitor. These electrodes are stored through the electrolytic reaction in the electrolyte. During the storage process of supercapacitors, charges are accumulated and stored on the electrode surface through redox reactions of electrons and ions in the electrolyte. The stored charges can be released through electrolyte reactions to realize energy output. Energy output refers to the release of stored energy from the supercapacitor, which is then converted into current output. Connecting the stored charge to an external circuit through wires enables the process. The current generated by the charge following through the circuit from the supercapacitor drives the external load to work.

DSSC have been widely investigated because of their theoretical photoelectric conversion properties and environmental friendliness (Table 1) [74], [114], [115], [116], [117], [118]. The performance improvement of integrated devices is typically limited because the CNTs used are usually presented in randomly dispersed structures, which has been addressed in numerous academic studies [117].

Table 1.

Parameters of dye-sensitized solar cell/supercapacitor integrated device.

Photoelectrodes	$J_{\mathit{SC}}$(mA/cm2)	VOC (V)	FF	${\eta }_{\text{D}SSC}$(%)	SC	$E_{\mathit{PSC}}$	${\eta }_{\text{overall}}$(%)	${\eta }_{\mathit{storage}}$(%)	Reference
TiO2 nano tube	9.03	0.63	0.5755	3.17	1.289 mF/cm2	6.662 × 108 Wh/cm2	1.64	51.6	Xu et al., 2014 [74]
TiO2/hb/CdS	17.3	0.746	/	6.11	155 F/g	13.7 Wh/kg	/	/	Das et al., 2018 [119]
ZnO Nanowire	2.0	0.45	0.3	0.27	2.89 F/g	/	/	/	Li et al., 2013 [123]
TiO2	11.96	0.63	0.34	2.6	/	/	3.72	/	Scalia et al., 2019 [122]
Graphene/CNTs/PANI fiber	0.076	0.6	/	4.2	472 mF/cm2	/	2.1	/	Liu et al., 2020 [121]
Silicon wafer	11.5	0.68	0.61	4.8	/	0.17 µWh/cm2	/	2.1	Cohn et al., 2015 [112]
TiO2	13.41	0.75	0.61	6.10	48 F/g	/	70	4.29	Yang et al., 2013 [118]

To fulfil the higher output voltage requirements for applications, the area capacitance of the double-electrode ATO device increased by 5.1 times to 1.100 mF/ cm² through selective plasma-assisted hydrogenation, and the integrated device demonstrated noteworthy the overall efficiency of 1.64% [74]. Das et al. prepared PEDOP@MnO₂ with a dual-function electrode for solar cells and SCs, in which a combination of hydrothermal methodologies and polymerization reactions have been utilized (Fig. 5a and b), and the working process of this integrations is exemplified in Fig. 5c and d [119].

Fig. 5.

(a) Diagram illustrating the preparation of electrode materials, the integrated device (b) and its (c-d) working process. Reproduced with permission [119].Copyright 2018, American Chemical Society.

As the widespread application of Pt is limited by its scarcity, high cost, ad susceptibility to corrosion. Common conductive polymers have been used as electrode materials to replace Pt because of their excellent redox reversibility. Hsu C Y et al. constructed an integrated three-electrode SCSD, employing PProDOT-Et₂ conductive polymer as the storage component for electronic storage (Fig. 6) [120]. During illumination, the charge voltage and discharge energy density of device reached 0.75 V and 21.3 µWh.cm⁻², respectively. Conductive polymers are a type of material with excellent redox reversibility, making them a potential substitute for traditional metal electrode materials. They exhibit higher electrochemical activity and stability, are less expensive, and easier to prepare. Additionally, their excellent flexibility and processability make them highly suitable for large-scale applications.

Fig. 6.

Structure diagram of SCSD based on DSSC. Reproduced with permission [120]. Copyright 2010, Elsevier.

Liu K et al. developed graphene/CNTs/polyaniline composite hollow fiber to replace Pt as electrode material [121]. The resulting device achieved an overall efficiency of 2.1%. Polymer can act not only replace Pt as an effective electrode material but also as a substitute for electrolyte. Polymers have the potential to replace platinum as an effective electrode material in integrated solar cell and supercapacitor devices. They can also serve as a substitute for electrolytes. Polymer electrodes are widely used in solar cells and supercapacitors due to their higher electrochemical activity and stability, lower cost, and ease of preparation compared to traditional metal electrode materials. Polymer electrodes offer excellent flexibility and machinability, making them highly suitable for large-scale applications. Additionally, polymers can serve as electrolyte substitutes. By optimizing the polymer structure, molecular weight, and doping degree in the integrated device, the electrochemical performance and stability of the polymer electrolyte can be further enhanced. Scalia A et al have successfully fabricated an electrode through Uv-induced photopolymerization utilizing multifunctional polymer electrolyte (Fig. 7) [122]. Furthermore, the performance and application range of polymer electrolyte can be enhanced by combining it with other materials, such as carbon nanotubes and metal oxides.

Fig. 7.

Diagram of integrated device, corresponding component and electrolyte. Reproduced with permission [122]. Copyright 2019, Elsevier.

At present, the sandwich structure often used in energy devices is easy to short-circuit between electrodes, the electrode active layer can detach, and the light transmittance is poor when the device is bent multiple times. Li et al. utilized ZnO nanowire arrays as the nanoscale component of the device for achieving a transparent and flexible planar photovoltaic device structure [123]. After undergoing repeated bending, the devices exhibited superior transmittance and performance compared to sandwich structures. Liquid electrolytes were chosen as charge transport materials for DSSCs. However, these electrolytes are volatile, easily leaked and have low chemical stability. These properties obstruct the further development of DSSCs, imposing significant technical challenges. In addition, the complex sealing process and energy-intensive preparation process will also raise the manufacturing cost of integrated devices. Therefore, it is becoming a research trend to pursue stable solid or quasi-solid electrolytes rather than liquid ones.

Integrated silicon solar cell/supercapacitor device

The mechanism of the silicon solar cell/supercapacitor integrated device involves two processes: light energy conversion and electrochemical energy storage. Silicon solar cells use the photovoltaic effect to convert sunlight into electrical energy. When sunlight hits the silicon solar cell, photons interact with the silicon material to produce electron-hole pairs. These electron-hole pairs are separated by the internal electric field of the silicon material, forming a current. The silicon solar cell generates electric energy which is then stored in the supercapacitor. During this process, ions in the electrolyte are adsorbed and desorbed on the electrode, forming an electric double layer that stores electric energy. The integrated device combines the processes of light energy conversion and electrochemical energy storage. When sunlight falls on the integrated device, the silicon solar cell converts light energy into electrical energy, which is then stored in the supercapacitor. This process enables rapid and efficient energy storage and release, opening up new possibilities for the field of energy storage and release in the future. Silicon solar cells usually consist either monocrystalline silicon, polycrystalline silicon or amorphous silicon. These materials provide stability, reliability, and generate a continuous direct current when illuminated. Owing to rapid advancements in microelectronics and screen-printing technology, this type of solar cell can be easily combined with supercapacitors and boost the system’s dynamic response. Nonetheless, it still remains a challenge to downsize energy storage equipment to match the planar geometry of microelectronic equipment. Thekkekara LV utilized graphene oxide scribed by laser as an energy storage module, downsizing the module’s physical dimensions without impeding its capabilities [124].

Rate and stability are essential criteria for evaluating the efficiency of integrated devices. Therefore, it is a prevalent approach to select SCSD with high charge/discharge rates. Graphene possesses a flat structure, which enables the quick transportation of electrolyte ions and allows for rapid charging and discharging. Liu H et al. used laser-scribed graphene sheets to make supercapacitors, and then used Au as an auxiliary electrode to integrated supercapacitor with silicon solar cell (Fig. 8) [125]. This integration method improves the SCSD 's efficiency and enhances its stability, reliability, and durability. The design concept of this integrated device utilizes the high conductivity and specific surface area of graphene, along with the stable electrochemical properties of Au, to achieve effective energy conversion and storage between solar cells and supercapacitors. This design considers both portability and expansibility of the equipment, providing new possibilities for future mobile energy equipment.

Fig. 8.

(a, c) Diagram of the integrated system and (b, d, e) SEM images of the cross section of silicon NWs, GO and (e) the laser-scribed graphene. Reproduced with permission [125]. Copyright 2018, American Chemical Society.

Tian prepared an asymmetric supercapacitor based on Mg ions using screen printing technology, the solar cell module has a distinctive design that can convert thermal radiation into electric energy and charge supercapacitors. This design allows integrated devices to provide stable power storage for electronic devices at any time [126]. This work presents a new design concept and implementation method for integrated solar cell and supercapacitor devices. This integrated device exhibits high efficiency, power density, and fast charge and discharge capabilities, as well as high stability, long lifespan, and low cost. These features offer new possibilities for future mobile energy equipment.

Liu modified the surface of silicon into a silicon nanowire array through etching, and the resulting nanowire spacing was larger and smoother by methylation, ultimately enhancing the adhesion effect of the transport layer PEDOT: PSS. In addition, a Ti electrode was evaporated on the back of the silicon wafer, considerably lowering the energy loss of the integrated devices (Fig. 9) [127]. Liu's research involved modifying the silicon surface into a silicon nanowire array using etching technology. The distance between the nanowires was increased by methylation, resulting in a brighter surface of the nanowires. These measures significantly enhanced the adhesion effect of the transport layer PEDOT: PSS on the silicon surface. Furthermore, Liu evaporated a titanium electrode onto the back of the silicon wafer, resulting in a significant reduction in energy consumption for both solar cells and supercapacitor integrated devices. This step has the potential to improve electron transmission efficiency, optimize current collection and distribution, and ultimately reduce energy conversion losses. This work not only enhances the energy efficiency of integrated devices but also improves their stability. The adoption of silicon nanowire array and methylation treatment has significantly improved the light absorption and PCE of solar cells. Additionally, the evaporated Ti electrode optimizes the electron transmission path, reduces energy loss, and improves equipment durability. Overall, it offers a new perspective and effective technical route for the integrated device design of solar cells and supercapacitors. The work enhances the energy efficiency and stability of integrated devices. Additionally, it offers valuable theoretical support and practical guidance for the advancement and implementation of clean energy technology.

Fig. 9.

(a) Structural diagram of device, (b, c) SEM and (d, e) TEM results of silicon nanoarray. Reproduced with permission [127]. Copyright 2017, American Chemical Society.

Organic solar cell/supercapacitor integrated device

The integrated devices of organic solar cells and supercapacitors work through the synergy between the photoelectric conversion characteristics of organic semiconductor materials and the energy storage characteristics of supercapacitors. Organic solar cells convert light energy into electric energy using the characteristics of organic semiconductor materials when exposed to illumination. Supercapacitors store energy by utilizing charge separation between electrodes and dielectrics. Organic semiconductor materials absorb light energy and convert it into electric energy, resulting in the formation of electron-hole pairs. These pairs are transported to the respective electrodes, creating an electric current. Additionally, electrons and ions migrate in the dielectric, storing charge through ion movement. Thus, the system converts light energy into electric energy and stores it in the supercapacitor, creating an integrated energy conversion and storage system. Because of the advantage of light weight, solution processing and large-area printing preparation, and the development of microelectronic technology presents a favorable opportunity for fabricating integrated SCSD on flexible substrates (Table 2). The current integration methods for organic solar cells/supercapacitors involve external interconnections of solar cells to supercapacitors [64], [79], [128], [129].

Table 2.

Parameters of organic solar cell/supercapacitor integrated device.

PC structure	${\eta }_{\text{D}SSC}$ (%)	ES electrolyte	SC	$E_{\mathit{PSC}}$	${\eta }_{\text{overall}}$(%)	${\eta }_{\mathit{storage}}$(%)	References
MWCNT/PEDOT:PSS/P3HT:PCBM/TiO2/Ti	1.01	MWCNT sheet/PVA	0.077 mF/cm	1.61 × 10−7 Wh/cm2	0.82	65.6	Zhang et al., 2014 [130]
ITO/PEDOT:PSS/P3HT:PCBM/Al	3.39	PVA-H3PO4	28 F/g	/	/	/	Das et al., 2018 [119]
Ag/Silicon nanowire/PEDOT:PSS/Al	12.18	H3PO4/PVA gel	234 mF/cm2	8.75 × 10−6 Wh/cm2	/	10.5	Li et al., 2017 [127]
ITO/PEDOT:PSS/P3HT:PCBM/Al/CNT	3.39	PVA-H3PO4	28 F/g	2.96 Wh/kg	/	/	Wee et al., 2010 [79]
ITO/ZnO/PBDTTT:OFT/PC71BM/MoOx/Ag	9.73	H2SO4:PVA gel	/	/	5.92	/	Liu et al., 2020 [64]

Liu fabricated organic solar cell onto a 40 µm thick CNTs /polymer-based material, achieving an overall efficiency of nearly 6% and an efficiency of over 96% after one week of 100 charge/discharge cycles were achieved, providing both high power and long-life devices (Fig. 10) [64]. However, the resistance of this connection results in energy loss and is unsuitable for roll-to-roll printing. CNTs are frequently employed as conductive electrodes in organic solar cells due to their excellent conductivity and processability. Wee G et al. utilized the CNT network as an integration platform, with self-supported polymer electrolyte was stacked on the top of the CNT network to create printable all-solid-state SCSD integrated devices [79]. This eliminates the need for charge storage interconnect in external solar cells and enhances performance.

Fig. 10.

(a) Schematic diagram and (b) photographs of device. Reproduced with permission [64]. Copyright 2020, Wiley.

To minimize the cost of materials and manufacturing processes, it is crucial to develop integrated devices with a straightforward structure that can easily combine with printed electronics technology. Srinivasan M employed a carbon nanotube network as the integrated platform for the all-solid organic SCSD and power control electrodes, which eliminated the internal resistance and reduce its weight [64]. It was also confirmed that CNTs are printable, all-solid state and cost-effective. Srinivasan M's research confirms the printability, all-solid-state characteristics, and cost-effectiveness of carbon nanotubes. This supports mass production of low-cost, high-performance integrated devices. The innovative design not only eliminates internal resistance but also reduces weight, providing new possibilities for developing integrated devices with a simple structure and easy combination with printed electronic technology. Optimizing the preparation process and control method of carbon nanotubes can enable the creation of an integrated device for all-solid-state organic solar cells and supercapacitors. This device is expected to have high efficiency, power density, and fast charge and discharge capabilities, providing a more efficient, lighter, and economical solution for future mobile energy equipment.

The use of organic solar cells in integrated devices offers potential benefits in manufacturing flexible or translucent devices. Zhang Z et al. have effectively fabricated the energy storage part by attaching PVA/H₃PO₄ electrolyte with titanium dioxide nanotubes, and MWCNTs were attached to form the energy storage part (Fig. 11a) [130]. The findings indicate that the integrated device exhibits rapid charging capabilities and remarkable electrochemical stability (Fig. 11b–e). The device integrates fast charging ability and remarkable electrochemical stability. This is attributed to the high PCE of organic solar cells, the excellent ionic conductivity of PVA/H₃PO₄ electrolyte, and the superior electrochemical performance of titanium dioxide nanotubes and MWCNTs.

Fig. 11.

(a) Structure, (b) the work process, (c) the charging and discharging image, (d) the constant current charging and discharging curve and (e) the cyclic voltammogram. Reproduced with permission [130]. Copyright 2013, Wiley.

Currently, researchers have made rapid advancements in organic SCSD through various strategies, including material design, device structure optimization and interface engineering. In the practical implementation of integrated devices, it is essential that solar cells exhibit robust stability, including thermal, water and mechanical stability. Furthermore, as the interface significantly affects the charge extraction process, modifying the cathode interface is a key strategy for improving performance effectively. By adjusting the energy levels at the cathode interface, it is possible to enhance compatibility and promotes stability of the device [80]. Furthermore, there have been no significant new breakthroughs in the mechanism research of integrated devices. The problem to be addressed in the future is the combination of machine learning to guide material synthesis.

Perovskite solar cells/supercapacitor integrated device

The perovskite solar cell/supercapacitor integrated device operates through two main processes: photoelectric conversion of sunlight and storage of electric energy. The first process involves the absorption of photons from sunlight by the surface of the perovskite solar cells, which excites electrons in the conduction band, creating electron-hole pairs. These pairs are then separated by a strong electric field and directed towards different electrodes, generating a current. The second process is electric energy storage. Supercapacitors function as charge storage devices for electric energy storage. They absorb excess charge from the solar cell when the output current is greater than the load consumption and store it. When the load requires current, the supercapacitor releases the stored electric energy and provides it to the load. The mechanism of the perovskite solar cell/supercapacitor integrated device is related to the circuit connection and control between them. In integrated devices, solar cells and supercapacitors are connected through appropriate circuits to ensure efficient energy conversion and storage. Furthermore, the optimal distribution of energy in the photovoltaic system can be achieved by controlling the voltage and current in the circuit, leading to improved system performance. When combined with supercapacitors, perovskite solar cells can improve overall system performance by providing superior efficiency (Table 3). Lee K et al. incorporated silver-containing epoxy resin electrodes to interconnect perovskite solar cells and supercapacitors in situ using PVA/phosphate solid state SCSD [131]. Liang J et al. integrated devices comprised of CsPbBr3-based perovskite solar cells, which demonstrated a fast light charging rate and stable cycle life, yielding excellent energy conversion efficiency [107]. Lee K and Liang 's research provides new design ideas and implementation methods for integrated perovskite solar cell and supercapacitor devices. This integration offers high efficiency, power density, and fast charge and discharge, as well as stability, longevity, and low cost. However, the research faces some challenges and limitations. For instance, research is still required to enhance the PCE and stability of perovskite solar cells, as well as to optimize the structure and performance of integrated devices to meet the requirements of various application scenarios.

Table 3.

Parameters of perovskite solar cell/supercapacitor integrated device.

PC structure	${\eta }_{\text{D}SSC}$(%)	ES electrolyte	SC	$E_{\mathit{PSC}}$	${\eta }_{\text{overall}}$(%)	${\eta }_{\mathit{storage}}$(%)	References
Ag/BCP/PCBM/MA1-yFAyPbI3-xClx/NiOx/ITO/PET	14.01	LiPF6	/	40 Wh/kg	8.41	80	Li et al., 2019 [141]
Ti wire/CNT fiber	2.2	NH4F/H2O	0.6 mF/cm2	1.5 × 10−7 Wh/cm2	1.5	68.4	Chen et al., 2012 [143]
FTO/WOx/MAPbI3/Spiro-OMeTAD/Au	14.14	KOH/PVA	27.1 F/g	/	2.13	/	Yang et al., 2020 [133]
ITO/PSS/PTAA/perovskite/PC61BM/PEI/Ag	16.10	PVA/H3PO4	144 F/g	/	10.97	80.31	Kim et al., 2013 [131]
FTO/c-TiO2/m-TiO2/CsPbBr3/nanocarbon	6.1	Silica gel	/	6.8 µWh/cm2	5.1	/	Liang et al., 2018 [107]
TiO2/ZrO2/MAPbI3/PEDOT-Carbon	6.37	LiClO4/CH3NH3I	/	7.83 × 10−7 Wh/cm2	4.70	73.77	Xu et al., 2016 [83]

Additionally, the flexible substrates commonly used (ITO/PEN, ITO/PET et al) can only withstand temperature of up to 60℃, which is lower than the annealing temperature (180 ℃-450 ℃) required for the electron transport layer. Therefore, it is crucial to develop flexible integrated devices that can be manufactured at lower temperatures [132], [133], [134], [135]. When designing integrated devices that combine flexible solar cells and supercapacitors, it is crucial to carefully select the appropriate electrolyte and electrode. Gel electrolytes are preferred due to their flexibility and ability to adapt to the deformation of the flexible substrate, which helps maintain device performance stability. Carbon materials, on the other hand, are highly conductive and stable, making them an effective choice for electrodes. (Fig. 12a) [136]. When compared to the inflexible integrated devices, the integrated flexible devices could only be charged to 0.65 V for an extended duration of 25 s under identical conditions (Fig. 12b and c). The integrated devices, whether they are rigid or flexible, indicate a complete PCE of 2.13% and 1.27%, correspondingly.

Fig. 12.

(a) Schematic diagram of integrated SCSD, and the charging-discharging curves of rigid (b) and flexible (c) device. Reproduced with permission [136]. Copyright 2020, Elsevier.

Among nanomaterials with many morphologies, those with regular and orderly structures can provide fast electron transport channels. Directional nanoarray structures on the other hand can puncture the passivation layer to form local conductive channels, thereby enabling effective electron extraction and transport, while maintaining high voltage and current in perovskite solar cells [137]. However, the brittleness and sensitivity to mechanical deformation of PET substrates limit their flexible application. In contrast to ITO/PET substrate, metal foil exhibits superior conductivity, heat resistance and mechanical strength [138], [139], [140]. To integrate a flexible device based on titanium dioxide tube arrays, Zhang F et al. utilized the symmetry of nanotubes to integrate flexible device based on titanium dioxide tube arrays (Fig. 13a and d), in which the MnO₂ was deposited on carbon fiber (CF)cloth-Co₉S₈ composite electrodes (Fig. 13b) [141]. The PVA/Au network was prepared by electrospinning and deposition (Fig. 13c). The PVA/Au network was prepared through electrospinning and deposition. It exhibits good conductivity and stability, providing reliable support and protection for flexible devices. Additionally, the PVA/Au network boasts high energy and power density, enabling fast charge and discharge and efficient energy storage. This device, based on a titanium dioxide tube array, has excellent PCE, electrochemical performance, and stability. It enables rapid conversion between light, electricity, and chemical energy, providing new possibilities for future mobile energy equipment.

Fig. 13.

(a) Structural diagram of the flexible optical SCSD, (b, c) Schematic diagram and SEM diagrams of CC-CO₉S₈-MnO₂ and Au electrodes, (d) Physical diagram of the flexible optical supercapacitor. Reproduced with permission [141]. Copyright 2018, Elsevier.

By combining supercapacitors to perovskite solar cells, Zhang et al. produced supercapacitors capable of rapid charge storage during photocharging (Fig. 14) [142]. The aim of this integrated device's design is to utilize the high PCE of perovskite solar cells and the high charge storage capacity of supercapacitors to achieve efficient and rapid energy storage and release. They combine perovskite solar cells and supercapacitors effectively, and skillfully use the high PCE of perovskite solar cells and the high charge storage capacity of supercapacitors, thus achieving the goal of fast charge storage in the process of light charging.

Fig. 14.

(a) Structure, (b)GCD curves and (c) applications of SCSD. Reproduced with permission [142]. Copyright 2022, Wiley.

Penh et al. developed the fibrous electrode as an electrode based on oriented TiO₂ nanotubes [143]. This linear device demonstrated an overall efficiency of 1.5% and is expected to be suitable for use in portable microelectronic devices. Perovskite solar cells are a rapidly developing photovoltaic technology. However, they suffer from serious instability caused by ion migration and illumination factors, resulting in a short lifespan. Future research will increasingly rely on the analysis and characterization of energy loss mechanisms in devices through advanced representation techniques. No matter which kind of solar cells are used, they can be combined with supercapacitors to achieve energy storage and enhance energy utilization. This combination offers greater adaptability and sustainability for clean energy applications and promotes the general efficiency and dependability of solar cell systems.

The stability issue of perovskite solar cells refers to their tendency to degrade and suffer damage during long-term operation. This instability primarily stems from the limited structural sensitivity and chemical stability of perovskite materials. These materials are susceptible to physical and chemical changes under environmental conditions such as light, humidity, and temperature, which can result in a decline in battery performance. To address the stability issue of perovskite solar cells, integrating them with supercapacitors can enhance their performance. Supercapacitors offer high energy density, fast charge–discharge rate, and good cycle stability, providing additional energy storage and stability support for perovskite solar cells. Compatibility and complementarity between the two should be considered when integrating supercapacitors. The electrochemical characteristics of supercapacitors must match the working voltage, current, and power of perovskite solar cells. Additionally, the integrated system must maintain stability to prevent battery degradation and capacitor damage. This can be achieved by optimizing the circuit design of batteries and capacitors, ensuring effective current distribution, and controlling temperature. Furthermore, the integration of perovskite solar cells and supercapacitors can be enhanced by optimizing the selection of materials and devices. This can be achieved by selecting perovskite materials with excellent chemical and structural stability, and utilizing high-performance capacitor materials to improve the overall performance and stability of the system. By considering compatibility and complementarity, optimizing circuit design, controlling temperature, and selecting materials and devices, the integration of perovskite solar cells and supercapacitors can effectively solve stability problems and improve working efficiency and lifespan.

Electrode materials and interface engineering

Electrode materials

Currently, various kinds of materials have been utilized as electrodes for SCSD, reported electrode materials predominantly comprise of carbon materials (CNTs, carbon aerogel et al.); polymers (polyaniline, polypyrrole et al.), metal compounds including sulfide, oxide, and various metal organic framework materials. Among these, carbon materials are most commonly used as electrode materials [144], [145], [146], [147]. In a conventional solar cell/supercapacitor integrated device, the sealing method employed to prevent electrolyte leakage leads to a complicated manufacturing process for the integrated devices.

Researchers designed new structures to effectively integrate supercapacitors and solar cells. This includes embedding supercapacitor electrodes into solar cells, or by installing solar cells on supercapacitors to optimize energy transfer and control. Shi C et al. utilized a photoanode composed of mesoporous titanium dioxide, and the energy conversion and storage units shared a common electrode, enabling the cooperative functionality between the units within a single electrolyte [81].

At low temperatures, supercapacitors usually experience a sharp decline in electrochemical performance because of the inhibition of ion diffusion in the electrolyte. However, the performance of supercapacitors at low temperatures is anticipated to significantly improve by employing electrode materials with photothermal performance, thereby achieving rapid temperature rise of the device through solar photothermal effect. Liu Z et al. employed a 3D multistage structure graphene electrode and proposed utilizing its photothermal effect to elevate the temperature of supercapacitors. This approach effectively enhanced the capacitance of pseudo capacitors and double-layer supercapacitors by approximately 1.5 times and 3.7 times respectively, thereby addressing the issue of energy storage device performance deterioration at low temperature [147]. The graphene electrode with a 3D multilevel structure exhibits excellent conductivity and stability, which effectively enhances the charge storage capacity and charge–discharge speed of supercapacitors. Additionally, the photothermal effect of graphene can increase the temperature of the supercapacitor at low temperatures, thereby improving its electrochemical performance and stability. Furthermore, adopting a graphene electrode with a 3D multi-level structure can reduce ultra-high voltage. This improves the internal resistance and weight of the capacitor, enhancing its cycle stability and lifespan. This method presents a novel idea and direction for the development of energy storage devices. Additionally, utilizing the photothermal effect of graphene can enhance the performance of energy storage devices at low temperatures, making them suitable for a wider range of applications. This method also provides a reference for researching other energy storage devices.

Integrated devices must possess strong temperature adaptability to guarantee excellent performance in diverse temperature environments. To enhance the temperature adaptability of integrated devices, it is important to optimize the conductivity of electrolyte, and carefully select appropriate packaging materials. Yu X et al. prepared a graphene/polypyrrole composite electrode with a 3D porous structure, with laser-induced and pulsed electrodeposition technology. They then constructed a photothermal enhanced supercapacitor on this basis [148]. Their findings demonstrated that exposure to solar irradiation (1 kW.m⁻²) quickly restored the heavily degraded electrochemical properties of the supercapacitors to room temperature. In addition, an extended and stable cycle life is crucial for ensuring the reliable operation of integrated devices. Ongoing research will prioritise mitigating the attenuation mechanism of capacitors and solar cells through measurements like inhibiting electrode material corrosion and dissolution, as well as regulating the electrochemical reaction of electrolytes to extend the service life of integrated devices.

Researchers have combined various materials into composites, making the most of their respective advantages and compensating for their defects to create electrode materials with specific capacities and excellent stability. While graphene or CNTs may possess excellent photoconductivity and photothermal effects, supercapacitors that are based on a physically mixture of CNTs/graphene often show limited photoresponse. Therefore, it is anticipated that high-efficiency supercapacitors can be constructed via the structural design of carbon electrode materials. The 3D self-supporting structure exhibits excellent photovoltaic and photothermal properties and improves charge transport between graphene and CNTs. It can effectively present the aggregation of graphene and CNTs, while providing adequate surface area for energy storage. The specific capacity of the constructed has doubled compared to that in the absence of light [149].

Interface engineering

The optimization of the interface is vital in enhancing energy transfer and conversion efficiency. Through surface modification, nanostructure design and interface engineering, one can enhance the contact between the supercapacitor’s electrode and solar cell. This reduces energy loss and resistance, thereby improving the energy transfer efficiency of the integrated device. Researchers are focusing on integrating flexible features into device structural designs. By using flexible substrates and nanomaterials to construct flexible electrodes and flexible cladding, the flexible integrated SCSD can be realized. Jin Z et al. prepared CF@TiO₂@MoS₂ coaxial nanocomposite fiber and constructed a fiber-like photoelectric conversion and energy storage integrated device (Fig. 15a) [150]. Among them, an optical fiber as a common electrode enables parallel “light-electricity-electrochemistry” energy acquisition and storage (Fig. 15b). Under solar illumination conditions, the supercapacitor part can be quickly charged in only 7 s, offering a novel concept for a flexible, wearable, self-powered energy system. Firstly, the CF@TiO₂@MoS₂ coaxial nanocomposites exhibit a high specific surface area, excellent light absorption performance, and a low energy band gap, which can effectively enhance the PCE. Additionally, the nanocomposite fiber possesses good electrical conductivity and electrochemical performance, making it suitable for use as an electrode material for supercapacitors and enabling rapid charge–discharge reactions. Furthermore, the fiber exhibits high levels of flexibility and extensibility, allowing it to conform to a range of bending and stretching environments. This study introduces a novel approach to developing flexible, wearable, and self-sustaining energy systems. The photoelectric conversion and energy storage functions are integrated in the same nano-composite fiber due to the excellent performance of flexible substrate and nano-materials. This integration greatly simplifies the system structure and improves energy efficiency and reliability. This flexible integrated SCSD technology is expected to have widespread use in smart wearable devices, portable electronic products, and foldable screens in the future. It will provide strong support for sustainable development and the promotion of clean energy.

Fig. 15.

(a) Schematic diagram of CF@TiO2@MoS2 coaxial fiber electrode applied in different devices, schematic diagram (b), SEM diagram (c), bending resistance test (d) and physical diagram of (e) CF@TiO2@MoS₂ electrode. Reproduced with permission [150]. Copyright 2017, Wiley.

Through precise control of nanostructure, researchers can adjust the PCE, capacitance and cycle life of integrated devices. For instance, by controlling the structure and morphology of materials, the electrochemical properties may be adjusted, thereby enhancing device performance. By adjusting the size, shape and arrangement of nanomaterials, it is possible to precisely control the charge storage and transport behavior. The disordered structure of dense stacking within the fiber electrode causes slow ion migration speed and limited stored charge, resulting in low energy density output. This is currently a bottleneck problem for development.

In response to the aforementioned issues, Meng et al. utilized a microfluidic confined assembly approach to construct a core–shell structure electrode with porous interior and ordered exterior [151]. The core–shell fiber electrode showed a substantial surface area (425.3 m².g⁻¹), and a wealth of ion channels (micro/mesoporous) to promote ion migration and excess storage in an effective manner. The constructed flexible supercapacitor has shown remarkable mechanical strength and electrochemical properties for fiber materials. Through the development of novel materials, interface engineering, regulation of structures and improved synthesis methods, researchers are dedicated to enhancing the performance and dependability of integrated devices. They aim to offer superior solutions for efficient energy conversion. To fulfill the requirements of efficiency and lifetime of integrated devices, future research will combine new technologies, surface modification and other control methods to attain precise control of the conductivity, light transmittance, specific capacitance of electrodes. The comprehensive performance of SCSDs will be improved by improving the composition and structure of the electrolyte, optimizing the integration process of capacitors and solar cells, and increasing the energy density of devices. Research in the future will be concentrated on upgrading the dependability and effectiveness of integrated technology, thereby expanding possibilities for their implementation in the renewable energy storage and power supply sector.

Integrated device function management

The integration devices encompass not only the structural integration of solar cells and supercapacitors, but also their energy matching. In addition to the device-level research, researchers also concentrated on the system-level implementation of integrated devices. They are dedicated to developing solutions for intelligent energy management systems, energy storage systems and electric transportation, as well as investigating ways to effectively merge integrated devices with other energy technologies. Aiming at the work process of integrated SCSD, it mainly comprises of three processes [46], [62], [75], [152], [153], [154]. The ${\mathrm{\eta }}_{\mathit{overall}}$ is calculated as follows [75], [155]:

$${\mathrm{\eta }}_{\mathit{overall}}={\mathrm{\eta }}_{L-E-C-E}={\mathrm{\eta }}_{L-E}\times {\mathrm{\eta }}_{E-C}\times {\mathrm{\eta }}_{C-E}=\frac{E_d}{P_{\mathit{in}}\times S_{\mathit{psc}}\times \mathrm{\Delta }t}\times 100\%$$ (1)

For integrated SCSD, the overall efficiency of the integrated devices is a very important evaluation index. This is primarily influenced by the PCE of devices, the efficiency of energy storage, the output voltage and so on. To account for the specific features of supercapacitors and solar cells, researchers have dedicated efforts towards developing efficient power management systems that enhance efficiency. This involves devising control strategies that can adjust to the dynamic charging and discharging processes to achieve optimized energy conversion and distribution. Due to the multifunctional components and structural complexity of integrated devices. Wu J et al. Proposed the ideal of functional combination management. They also presented three-terminal integrated devices featuring perovskite solar cells and supercapacitors (Fig. 16a, b, and d) [155]. The overlap of maximum power points efficiencies was sought (Fig. 16c, e, and f), so as to surpass the 20% threshold for device performance.

Fig. 16.

(a-f) Performance of SCSD. Reproduced with permission [155]. Copyright 2022, Elsevier.

Effective matching and collaboration between supercapacitors and solar cells are necessary for integration into one system. Researchers aim to achieve a dynamic energy balance and optimal working conditions between solar cells and capacitors by employing intelligent control algorithms and optimization strategies. Gao X P et al. Have integrated perovskite solar cells with water-based supercapacitors. By using Janus' strategy of electrodes sharing and introducing gel electrolyte, a quasi-solid integration of optical storage devices was constructed [156]. Through the time scale-based collecting/releasing strategy, it can effectively reduce the reliance of solar cells on illumination and reduce the need for ordinary capacitors to require electric energy input. Furthermore, it can notably enhance the practicality of solar energy. However, because of the challenge in matching energy conversion, the integrated device system may often appear disordered and cumbersome. Based on this, Kim et al. utilized screen-printing technology to integrate miniature magnesium ion-based supercapacitors with silicon solar cells [131]. Among these, they assembled asymmetric supercapacitors with anode material consisting of manganese dioxide, cathode material vanadium nitride, magnesium sulfate electrolyte and polyacrylamide gel electrolyte. The output voltage of the 2.2 V capacitor correlates favorably with that of solar cell (2.5 V). This correlation is advantageous to achieving high PCE (5.2%) in the fully flexible self-powered system. Additionally, the device’s cycle performance is enhanced, presenting a new approach to building integrated and wearable self-powered devices. Solar energy collection and storage integrated device experiences low efficiency during the process of solar energy harvesting.

To achieve this aim, Song et al. synthesized Ni (HCO₃)₂@Ni anode material, which Features a core–shell structure. They further constructed a hybrid supercapacitor (VAHSC) with a window voltage that is adjustable and electrodes with different internal capacities [157]. The research into the integration of supercapacitors and solar cells has made significant strides. Future endeavors will continuously promote the development and feasible implementation of integrated devices by establishing efficient power management systems, streamlining circuit topology, fostering collaboration between solar cells and capacitors, facilitating fault detection and management and validating practical applications.

In fact, when selecting capacitors to integrate with solar cells, several factors need to be considered, including working voltage, energy density, power density, cycle life, and cost. The capacitor must match the output voltage of the solar cell. Since the output voltage range of solar cells is wide, the selected capacitor should be able to function correctly within this range. Energy density and power density are important indicators of capacitor performance. Capacitors with high energy density and power density can store more electric energy and supply current to the load faster, improving the efficiency and performance of a solar cell system. Additionally, cycle life is a key index for the stability and reliability of capacitors. Choosing capacitors with a long cycle life can ensure the long-term stable operation of a solar cell system. Finally, when selecting capacitors, it is necessary to consider cost as a factor. Although high-cost capacitors may provide better performance, in some application scenarios, low-cost capacitors may be more suitable. Therefore, it is necessary to weigh them according to the application scenarios and requirements. When selecting capacitors for integration with solar cells, it is important to consider various factors such as working voltage, energy density, power density, cycle life, and cost. Different types of capacitors can be chosen based on specific application scenarios and requirements to meet the system's needs.

Conclusions

The research on SCSD is crucial for promoting the development of renewable energy. However, there are still some research difficulties that need to be overcome, which are also the research focus that requires attention. Solar cells and supercapacitors have significant differences in working principles and material systems. Currently, integrated devices are encountering challenges in enhancing their efficiency and stability. Although the PCE of solar cells is high, there is still room for improvement. Additionally, the energy storage density and energy conversion efficiency of supercapacitors require further improvement. One of the challenges in current research is ensuring the performance of devices under different working conditions, such as temperature, humidity, and illumination. Integrated devices are often limited in their use for some application scenarios due to the need for a large volume to accommodate batteries and supercapacitors. The design of integrated devices must consider the functional requirements of solar cells and supercapacitors to ensure effective photovoltaic conversion and efficient energy storage. Therefore, designing an efficient, stable and lightweight structure is a current research challenge. Long-term use may degrade solar cells and supercapacitors, affecting their performance and lifespan. Finding more durable materials and improving the stability of device is a challenging problem. Currently, the production cost of solar cells and supercapacitors remains high. Reducing cost and ensuring material recycling are also ongoing research challenges.

To address the aforementioned challenges, future research will concentrate on enhancing the PCE and energy storage performance of integrated devices by optimizing their structural design. Additionally, it is necessary to conduct further research on efficient and stable photoelectric and electrode materials to enhance the overall performance of integrated devices. Another research focus is the development of new integrated device structures, such as composite materials and multi-layer structures, to enhance device performance and stability. Additionally, exploring new integration methods to improve efficiency and ease of use is necessary. Research on material surface coating is conducted to enhance the oxidation resistance of solar cells and supercapacitors, thereby prolonging device service life. Researching and developing low-cost and recyclable material systems is key to reducing the overall cost of integrated devices. Additionally, it is necessary to research and develop efficient and environmentally friendly manufacturing processes to reduce production cost and improve production efficiency. SCSD have shown progress in the field of efficient energy conversion and storage. Integrated solar cells and supercapacitors have shown progress as an efficient solution for energy conversion and storage. However, technical challenges remain, such as energy matching, interface optimization, and cycle stability between the two components. Further research should focus on addressing these challenges to achieve optimal energy conversion and storage.

The continuous research and development of new materials, along with the application of advanced technology, will lead to an improvement in the conversion efficiency of solar cells and supercapacitors. This, in turn, will result in higher performance integrated devices. The development of nanotechnology and microelectronics will enable SCSD to be smaller and lighter, making them suitable for a wider range of applications. The production process of SCSD can be made more environmentally friendly and sustainable through the use of renewable materials, green manufacturing, and other measures. These measures include designing new structures, developing high-efficiency photoelectric and electrode materials, and exploring low-cost manufacturing technology. This will contribute significantly to the development of renewable energy.

Further advancements in integrated SCSD will accelerate the proliferation of renewable sources such as solar energy. Ongoing research predominantly concentrates on material optimization, structural design, functional improvement and system integration. As innovation and exploration continue, the integrated SCSD are anticipated to achieve significant breakthroughs and increased applications in the future. Future integrated devices will enhance the efficiency of energy systems by optimizing energy transfer and management between solar cells and capacitors, thus enabling greater efficiency. The integrated devices use advanced energy control algorithms to provide real-time monitoring, optimization and energy scheduling to better satisfy user demand. The integration of these devices is anticipated to incentivize the development of smart energy management systems. Future research will combine theoretical calculation methods with in-situ analysis and testing technology to thoroughly discuss the spatial distribution of atoms and active sites within electrode materials, their relationship with surface potential, and the charge density distribution at the interface of integrated devices.

To satisfy the demands of attaining the practical application of integrated devices, it is important to investigate the structural modifications of individual component materials that occur during ion dynamics throughout the energy storage process. Further research will focus on the transfer of charges within the interface, improving the efficiency of conversion, examining the structural stability, and enhancing the lifetime of integrated solar cell/supercapacitor systems. Through further mechanism research, there will be an exploration of new electrode types and active materials. Integrated devices are anticipated to increase energy conversion and storage efficiency, encourage renewable energy adoption, support sustainability and deliver dependable power solutions for electric transportation and microgrid systems.

Compliance with ethics requirements

This article does not contain any studies with human or animal subjects.

CRediT authorship contribution statement

Qiaoling Zhang: Formal analysis, Writing – review & editing. Guodong Li: Formal analysis, Writing – review & editing. Fen Qiao: Supervision, Writing – review & editing, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Biographies

QiaolingZhang, she received his Ph.D. from Xi 'an Jiaotong University in September 2013 and is currently an associate professor at Xi 'an University of Technology. Her research focuses on the theory and technology of clean energy utilization. She has presided over more than 10 projects such as the National Natural Science Foundation and the Natural Science Foundation of Shaanxi Province, published more than 20 academic papers, authorized 3 national patents and 1 software copyright.

GuodongLi, he graduated from Xi 'an University of Technology and is currently a professor at Xi 'an University of Technology. His research focuses on clean energy use. He has published more than 70 academic papers, of which more than 20 were indexed by SCI and EI. He has published 1 monograph and 3 textbooks and has presided over or mainly completed more than 40 various scientific research projects.

FenQiao, she received her Ph.D. degree from Dalian University of Technology in 2010, From 2010 to 2012, she worked as a postdoctoral researcher in Liberato Manna’s group at Italian Institute of Technology (IIT), Italy. And then worked at Jiangsu University as an associate professor. Her current research interests mainly focused on the design of functional semiconductor nanocrystals and their applications in optoelectronic devices. She has published more than 100 papers in international journals.