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. 2024 Mar 21;9(16):18202–18211. doi: 10.1021/acsomega.3c10388

Bandgap Engineering and Enhancing Optoelectronic Performance of a Lead-Free Double Perovskite Cs2AgBiBr6 Solar Cell via Al Doping

Asad Ullah †, Muhammad Iftikhar Khan †,*, Ihtisham-ul-haq †, Badriah S Almutairi ‡, Dalil Bulayis N AlResheedi §, Jeong Ryeol Choi ∥,*
PMCID: PMC11044255  PMID: 38680326

Abstract

graphic file with name ao3c10388_0006.jpg

In this study, solar cells based on pure Cs2AgBiBr6 and Al-doped metal were fabricated using the sol–gel spin-coating technique. X-ray diffraction (XRD) analysis confirmed the formation of cubic-structured films for both pure and Al-doped. Notably, the grain size of Al-doped Cs2AgBiBr6 was observed to be larger than that of its pure counterpart. The optical properties of these films were investigated using UV–vis spectroscopy, revealing essential parameters such as the bandgap energy (Eg), refractive index (n), extinction coefficients (k), and dielectric constant. While the pure film exhibited an Eg of 1.91 eV, the Al-doped film demonstrated a slightly lower Eg of 1.82 eV. Utilization of these films in solar cell fabrication yielded intriguing results. The J–V curve shows that the pure solar cell displayed a short-circuit current density (Jsc) of 5.01 mA/cm2, a fill factor (FF) of 0.67, an open-circuit voltage (Voc) of 0.89 V, and an efficiency of 3.02%. Al doping led to improvements, with an increase in Voc to 0.91 V, FF to 0.71, and Jsc to 5.29 mA/cm2. Consequently, the overall efficiency surged to 3.40%, marking a substantial 12.5% enhancement compared with the pure solar cell. These findings underscore the efficacy of Al doping in enhancing the performance of Cs2AgBiBr6-based solar cells.

1. Introduction

The need for energy is growing worldwide, and as fossil fuels become scarcer, there is a noticeable movement in favor of obtaining alternate energy sources, particularly when it comes to environmentally friendly energy options.1,2 For a number of reasons, solar energy has become a popular substitute for fossil fuels. It is an essential part of the switch to renewable energy sources because of its abundance, advantages for the environment, affordability, and potential for energy independence.3−5 As a consequence, solar energy, harnessed through photovoltaic technology, has become a leading contender as a clean and sustainable alternative to fossil fuels. In particular, metal halide perovskites have gained significant attention and interest in recent years.6,7 Metal halide perovskites, described by the general chemical formula ABX3, was considered: A cations here is a choice between CH3NH3+ (MA+), CH(NH2)2+ (FA+), or Cs+ (cesium), B cations as Pb2+, and X anions as Cl–, Br–, or I–.8−10 Perovskite solar cells (PSCs) exhibit exceptional performance due to their unique characteristics, which include a high absorption coefficient, a direct and modifiable bandgap, balanced electron and hole transport, an extended carrier diffusion length, and favorable charge carrier mobilities.11 Furthermore, PSCs show a great deal of promise when used in place of traditional solar devices. In a few years, PSCs’ power conversion efficiency (PCE) increased significantly, from 3.8 to 22.1%.12,13 On the other hand, lead halide perovskites’ instability and the ongoing problems with health and the environment have made commercialization difficult. These shortcomings are primarily associated with the leaching of Pb2+ ions due to their water solubility.14,15 Less toxic ions such as Sn2+, Bi3+, Ge2+, Sb3+, Mn2+, and Cu2+ offer a promising alternative to Pb2+ in perovskites, allowing for the creation of new lead-free perovskite structures. The incorporation of these metal cations not only broadens the range of perovskite variants but also promotes the development of PSCs in an environmentally friendly way.16,17 The fact that these solar cells have shown reduced PCE in comparison to Pb-based perovskite cells is noteworthy. The discovery of Pb-free halide double perovskites (LFHDPs), which have the chemical formula A2B′B″X6, has recently led to the possibility of a solution. In LFHDPs, two bivalent metallic Pb2+ cations are substituted with one monovalent and one trivalent cation, leading to a modification in the dimensionality within the crystal structure.18,19 Because of its versatility in terms of composition and structure, multiple cation substitution is acknowledged as one of the most effective methods within the context of LFHDPs. The Goldschmidt tolerance factor (GT) and octahedral factors (OF) play essential roles in the quest for appropriate and stable perovskite structures.20 Among the LFHDPs under examination, only a limited number of perovskite materials have met the necessary criteria for integration into solar cell applications. Significantly, Cs2AgBiBr6 has become one of the most widely adopted absorbers in LFHDP solar cells.20−22

The above-mentioned consequence for Cs2AgBiBr6 is primarily attributed to its notable characteristics, including a high carrier lifetime, relatively small carrier effective mass, strong moisture stability, and low toxicity. While Cs2AgBiBr6 solar cells have demonstrated a modest power conversion efficiency (PCE) of around 3%, they exhibit highly promising exceptional physicochemical properties such as extended carrier lifetimes, robust elasticity, resistance to thermal expansion, long-term stability, and nontoxicity.23−25 However, Cs2AgBiBr6 also shows several disadvantages, including the presence of prominent surface imperfections, the extensiveness of the electron–phonon interaction, the presence of excitons, and difficulties in the manufacturing process, which are particular issues related to low solubility and the requirement for high-temperature phases.20,26 Despite comprehensive efforts aimed at enhancing solar cell architectures with the film formation and preparation for this material, the efficiency has only managed to reach 2.4%.27,28 The limited efficiency primarily results from the wide bandgap and weak light absorption, while the latter issue arises from the material’s indirect bandgap. To address this challenge, it is necessary to modify the band structure of the material.29−31 Multiple effective strategies have been devised to boost the performance of LFHDPs, including partial substitution at the A-site, B-site, or B″-site, chemical substitution, and the incorporation of heterostructure interfaces. Among these approaches, doping stands out as especially well-suited due to its simplicity and straightforward implementation. Furthermore, it offers the advantage of adjusting the LFHDP properties without the need to alter the crystal structure. To tackle the aforementioned difficulties, Al doping into Cs2AgBiBr6 has been carried out. Because of its capacity to improve stability, lower the bandgap, and increase conductivity, all of which ensure that films have enhanced electrical and optical properties, Al doping has attracted a lot of attention. Furthermore, doping effectively reduces the annihilation of electron–hole pairs, leading to the presence of free electrons in the conduction band and consequently lowering electrical resistance.32−36 Additionally, Al doping encourages grain elongation. This increase in grain sizes in perovskite films is associated with increased crystallinity, which is a desirable property for reducing flaws and enhancing the stability of perovskite-based devices. The improved crystalline structure is essential for improving charge transfer in the perovskite layer, which is necessary to increase the solar cell efficiency. Larger grains are advantageous for charge.37−39

This work presents a novel examination into effective Al integration into Cs2AgBiBr6, a promising LFHDP material. Comprehensive characterizations using UV–vis spectroscopy, solar simulator measurements, and X-ray diffraction (XRD) were performed on produced Al-doped Cs2AgBiBr6. The material’s crystalline structure and phase purity were clarified by the XRD investigation, which also shed light on how Al doping affected the perovskite lattice. The optical properties were investigated using UV–vis spectroscopy, which showed variations in the absorption spectra that were suggestive of moderation in the electronic system. In addition, experiments using a solar simulator were carried out to evaluate the photolysis efficiency and execution of Al-doped Cs2AgBiBr6 as a possible photovoltaic application candidate. A thorough grasp of the constructional, optical, and photo offset characteristics of the new Al-doped Cs2AgBiBr6 is provided by the combined use of various characterization approaches, which makes a significant contribution to the developing field of LFHDP materials for sustainable energy technologies.

2. Experimental Section

Like other perovskite materials, double perovskites are susceptible to light, oxygen, and moisture in the environment. The limited solubility of the precursors needed for the production of Cs2AgBiBr6, a type of double perovskite, makes it difficult to fabricate high-quality films; therefore, the synthesis of this material is usually not done in ambient air. The fabrication of Cs2AgBiBr6 films is done under high vacuum conditions. This helps to achieve double perovskite Cs2AgBiBr6 films with excellent crystallinity, flatness, and absence of pinholes. The process often involves annealing at high temperatures (at least 280 °C) in a controlled atmosphere, such as a nitrogen-filled glovebox. This helps to fully convert the precursors into Cs2AgBiBr6 and obtain high-quality films.27,40,41

Bismuth bromide (BiBr3, 98%) and cesium bromide (CsBr, 99.9%) were obtained from Sigma-Aldrich. Sigma-Aldrich was also the source of isopropanol (IPA, 99.5%), hydroiodic acid (HI, 57 wt % in H2O, 99.95%), dimethyl sulfoxide (DMSO, anhydrous, 99.8%), and chlorobenzene (CB, 99.8%). We bought silver bromide (AgBr, 99.998%) from Alfa-Aesar. Greatcell Solar Materials provided the formamidinium iodide (FAI, >99.99%), guanidinium iodide (GAI, >99%), and methylammonium iodide (MAI, >99.99%). None of the solvents needed to be further purified before use. The resulting composition was stirred at 120 °C until the solvents evaporated, leaving behind crimson-hued crystals. Maxing was halted, and then gradually cooled with an hourly rate of 5 °C. The set of components was then left undisturbed for an entire night. Following their precipitation, the red crystals were separated and collected by filtration. Following this, they underwent an ethanol wash. The resulting solid product was dried in a vacuum at 60 °C, yielding the development of Cs2AgBiBr6 crystals. The same process was repeated for Al doping, with 5% Al incorporated with every chemical constituent. Particle size and phase composition of pure and Al-doped Cs2AgBiBr6 films were examined through XRD analysis. XRD was conducted using a Panalytical Empirian diffractometer configured in the Bragg–Brentano setup, employing Cu Kα radiation (λ = 1.54 Å), within the range of 2θ = 10–70°. The absorption spectra were acquired using a Shimadzu UV–vis spectrophotometer UV-2600 to further investigate the optical properties of the materials.

To create a precursor solution for both pure Cs2AgBiBr6 and Al-doped variants, initially dissolved in 1 mL of DMSO solvent, AgBr (0.5 mg, 93.9 mmol), CsBr (1.0 mg, 212.8 mg), and BiBr3 (0.5 mmol, 224.3 mg) were combined. Subsequently, the mixture was subjected to heating at 75 °C for several hours, ultimately resulting in the development of a light-yellow mixture. The deposition of the Cs2AgBiBr6 and Al-doped films was carried out by using the spin-coating method. Specifically, 100 μL of these mixtures were applied via spin-coating onto the glass/FTO/TiO2 layers at a rotational speed of 3000 rpm for a duration of 1 min. To achieve the generation of the double perovskite phase, the resulting film was heated up for 5 min at 280 °C. The construction of solar cells utilizing these films was performed on TiO2/FTO/glass substrates, following the fabrication method previously detailed in our earlier work.42

To produce the hole transport material (HTM), an initial solution (A) was prepared by combining 36 mL of tributylphosphate (TBP). Using 22 mL of a prepared solution that contained 520 mg/mL lithium bis-trifluoromethyl sulfonyl imide. Within solution (A), we introduced and stirred 72 mg of spiro-OMeTAD. This process resulted in the development of a solution, now termed as solution (B). To create the final solution, we incorporated 1.0 mL of chlorobenzene into solution (B). To better the photoactive layer’s wettability, extend the performance duration, and enhance the device’s connectivity, we coated the electrode with an 80 nm-thick layer of gold using an external source. These solar cells featured an active area measuring 0.16 cm2. As shown in Figure 1b, the solar cell’s layer configuration was as follows: glass/FTO/TiO2/Cs2AgBiBr6/spiro-OMeTAD/Au. A solar simulator with a calibrated air mass (AM) of 1.5 G and an intensity of 100 mW/cm2 was used to test the solar cells. Another feature of the testing gear was a computer-controlled source meter, a Keithley 2400 (produced by Keithley Instruments, Inc., Cleveland, OH, USA). The J–V curve was produced with this configuration. The voltage sweep was carried out between 1.2 and 0 V in the reverse bias direction. The device was tested with an AM of 1.5 and standard 1 sun illumination. The voltage sweep was carried out at a scan rate of 0.2 V/s.43

Figure 1.

Figure 1

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(a) Schematic diagram of crystal structure of double perovskites. (b) Step-by-step coating of layers: FTO, TiO2, perovskite, spiro-OMeTAD, and Au.

3. Results and Discussion

3.1. Structural Analysis

The XRD analysis shows that the synthesized material consists entirely of the pure-phase Cs2AgBiBr6, with no traces of any other secondary phases, as depicted in Figure 2a. Cs2AgBiBr6 possesses crystallizes in a cubic elpasolite structure with Fm3m symmetry.44 These parameters closely match those found in the standard JCPDS data with the file number (01-084-8699). The presence of all odd Miller indices in the XRD pattern suggests that Ag+ and Bi3+ ions exhibit a rock salt ordering within the structure. The lattice parameter for Cs2AgBiBr6 is approximately equal to a = 10.9 Å, but for doping of Al, its value becomes 11.1 Å, which is consistent with the values reported in the literature.8 The primary peaks in the XRD pattern for pure Cs2AgBiBr6 were analyzed at 2θ angles of 16.1, 22.3, 27.3, 32.6, 36.4, and 38.4°, corresponding to the crystallographic indices (hkl) of (200), (220), (222), (400), (420), and (440), respectively, as shown in Figure 2a. Observation from the XRD pattern revealed that these peaks exhibited a slight shift toward a lower angle by Al doping. The main peak of (400) at 32.6° for pure was shifted by doping leftward, resulting in 32.2° showing a difference of 0.4°. This shift in peak positions results in a decrease in 2θ which implies an expansion of the interplanar spacing (d-spacing) between the crystal lattice planes.38 The observed shift in the peaks serves as evidence of the successful doping of Al into Cs2AgBiBr6, and no additional phases or Al-related peaks were detected, confirming the material’s purity. It can also be seen that the intensity of the peaks is enhanced by doping, which is in correspondence with the crystallinity of the material. By increasing the intensity of the peaks, the strain is produced in the crystal lattice because of the insertion of the Al(3p1).45

Figure 2.

Figure 2

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(a) XRD pattern for undoped and Al-doped Cs2AgBiBr6 halide double perovskite solar cell and zoom-in for clear vision of shifting of 2θ degree of the (400) plane. (b) Crystallite size and dislocation line density of undoped and doped. (c) d-Spacing and lattice parameter. (d) Volume of pure and doped.

Ag and Bi alternately occupy the cores of the octahedra in all three orientations with Cs+ occupying the central position within the cuboctahedral cavity. This arrangement results in a supercubic structure, as illustrated in Figure 1a. Furthermore, inverted planar heterojunction perovskite solar cells (PSCs) were fabricated with the device structure glass/FTO/TiO2/Cs2AgBiBr6/spiro-OMeTAD/Au as shown in Figure 1b. To enable interparticle electron transfer and close contact between the two polymorphs is necessary. The critical factor for this intimate contact lies in their crystallite size. The crystallite size can be calculated by the Scherrer equation46:

3.1. 1

where K is a constant. The eq 1 establishes a connection between the crystallite size (D) and various attributes of the diffraction peak such as the wavelength of the X-ray beam (λ), the full-width at half-maximum (fwhm) of the peak (β), and the Bragg angle (θ). The peaks (400) and (220) were chosen for crystallite size measurement considering their high intensities. Consequently, the crystallite size for the pristine Cs2AgBiBr6 measures 32 nm, whereas for the doped materials, it extends to 38 nm as shown in Figure 2b. Hence, it can be concluded that the increase in crystallite size is due to the Al dopant having a greater ionic radius than the host Ag. Dislocation line density is a crucial parameter employed for assessing the existence and concentration of dislocations within a crystalline material. The unit of measurement for dislocation line density is expressed as m/m3 and given by the relation47:

3.1. 2

The dislocation line density for the pristine material is 9.7 × 10–4, while for the doped material, it is reduced to 6.9 × 10–4 as shown in Figure 2b. This decrease in dislocation density with Al doping in Cs2AgBiBr6 films may be attributed to the difference in ionic sizes between Al3+ and Ag+ within the Cs2AgBiBr6 lattice which increases crystal perfection.48 A crucial quantity in X-ray diffraction analysis, interplanar d-spacing (d), is used to determine the crystal structure of a material. The 'd' signifies the perpendicular distance between two consecutive crystallographic planes of atoms within a crystal lattice. In the context of the Al-doped Cs2AgBiBr6 double perovskite, the values of this 'd' can be computed from the diffraction peak positions (2θ) corresponding to various diffraction planes (hkl) utilizing Bragg’s law49:

3.1. 3

It is a well-established fact that diffraction peaks undergo displacement and broadening under stress or strain effects. For undoped Cs2AgBiBr6, the measured d-spacing for the most intense reflection (100%) at a 2θ value of 32.6 peaks in the observed powder patterns was 2.74 Å. Upon doping, a slight shift in this d-spacing to 2.77 Å was detected. Given the lack of significant displacement, we infer that the dopant’s strain is negligible. Our calculation of crystallite size using Scherrer’s line broadening can be justified as depicted in Figure 2b, where the d-spacing values are presented in Figure 2c. This increase in 'd' suggests a change in the crystal lattice. It is worth noting that the lattice parameter (a) is found to increase in the order of F < Cl < Br-based double perovskites. This increase can be attributed to the enlargement of atomic size.50 Furthermore, the increase in the lattice parameters following 5 wt % Al doping is attributed to the films experiencing tensile strain along their c-axis. Additionally, the doping of 5 wt % which was not detected in XRD might induce a change in the 'a' value.51,52 Lattice parameter and volume can be calculated by formulas:

3.1. 4
3.1. 5

The 'a' value for pure Cs2AgBiBr6 was 10.9 Å after doping its value increased to 11.1 Å as shown in Figure 2c. The lattice parameters of the samples were determined by selecting diffraction peaks from the crystal planes (220), (222), and (400). The alterations in lattice parameters due to doping manifested as a slight elongation of the 'c'-axis, while “a' and 'b” remained nearly constant. As only the 'c' parameter exhibited marginal changes, it can be inferred that the dopants occupied both bcc and fcc positions within the structure.53 The volume for pure was 2.20 × 10–8 m3, and for doped, it becomes 2.23 × 10–8 m3 as shown in Figure 2d. The distinction in structural properties between the pristine and 5% Al-doped Cs2AgBiBr6 double perovskites is evident. The expansion in the d-values for the Al-doped Cs2AgBiBr6 double perovskites, compared to the undoped counterpart, serves as clear evidence of the successful incorporation of Al into the Cs2AgBiBr6. By introducing Al3+ through doping, it is possible that the [BiBr6]−3 octahedra in the Cs2AgBiBr6 double perovskite lattice could be replaced by [TiBr6]−3 octahedra. This substitution is attributed to the notable electronegativity gap between Al (1.61) and Cs (0.79), in addition to the charge disparity between Al3+ and Cs+. However, the replacement of Cs by Ag ions in the Cs2AgBiBr6 lattice is unlikely due to the differences in the electronegativity and charge. Conversely, the electronegativity of Al (1.61) is relatively similar to those of Ag (1.93) and Bi (2.0), and there is a charge whose equilibrium is more effectively maintained by Bi3+ and Al3+ as compared to Bi3+ and Ag+. Consequently, it is expected that the substitution of [TiBr6]−3 octahedra for [BiBr6]−3 octahedra is a more dominant process in the formation of the Al-doped Cs2AgBiBr6 lattice.54

3.2. Optical Analysis

To calculate the bandgap energy (Eg) of both the pure Cs2AgBiBr6 and Al-doped films, a graph was generated by plotting (αhν) against the energy of photons (hν), as depicted in Figure 3a. In this figure, α quantifies the light absorption, ν represents the frequency of light, and h symbolizes Planck’s constant. The bandgap energy is determined using Tauc’s relation55,56:

3.2. 6

where 'n' is a numerical factor and 'A' is a constant of proportionality. The exponent in this equation is typically represented as n = 1/2 for the materials that exhibit direct allowed transitions. The optical bandgap of the pristine Cs2AgBiBr6 was 1.91 eV, consistent with previously reported values for Cs2AgBiBr6.57 In contrast, Eg of the Al-doped Cs2AgBiBr6 was determined to be 1.82 eV as calculated from the UV–vis spectroscopy result shown in Figure 3a, signifying a significant reduction in bandgap when compared to the undoped film. This suggests that Al doping offers a more versatile means of tuning the bandgap, subsequently altering the electronic structure and optical properties. Reducing the bandgap is crucial in solar cells as it enhances the absorption of photons within the solar spectrum. This enhancement results in a higher photocurrent production by the cell.58−60 At the same time, the increased interaction between Al-3p and Ag-5s states results in a broader conduction band, causing the density of states to shift toward lower energy levels. In the case of Al-doped Cs2AgBiBr6, this shift leads to the upward movement of the Fermi level into the conduction band, facilitating the formation of an n-type semiconductor. This adjustment eases optical transitions and enhances the overall optical characteristics of the material.61,62 Therefore, the Al doping introduces new energy levels into the bands of Cs2AgBiBr6 subsequently reducing the bandgap between the valence and conduction bands in thin films of Cs2AgBiBr6.

Figure 3.

Figure 3

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(a) Eg of pure and Al-doped Cs2AgBiBr6 films and (b) refractive index, optical electronegativity, and extinction coefficient of pure and doped Al–Cs2AgBiBr6.

The refractive index (n) is a critical physical parameter that directly correlates with the atomic interactions at the microscopic level.61,63 The n for both pure and Al-doped thin films was determined through the following equation:

3.2. 7

where A and B are constants having values 13.6 and 3.4 eV, respectively. The value (n) for pristine Cs2AgBiBr6 was 2.74 and the value of doped Al increased to 2.79 as shown by the graph in Figure 3b. The rise in the refractive index 'n' can be attributed to a reduction in the bandgap resulting from Al doping causing the medium to become denser. Consequently, light is bent more significantly, indicating increased light scattering, which is advantageous for solar cells64,65. This increase in 'n' also corresponds to high polarizability associated with larger atomic radii. Notably, the 'n' achieves its maximum value within the visible region for these compounds, which suggests their promising prospects for use in optoelectronic applications. The rise in the 'n' of Cs2AgBiBr6 thin films may be attributed to the increased film densification and pore filling resulting through the Al doping process.66,67

Electronegativity is a property of an element or atom that reflects its tendency to attract electrons. It provides important insights into the nature of chemical bonding and the type of bond that forms between two atoms. The Pauling scale is a commonly used scale for electronegativity values. When the electronegativity difference (ΔEN) between two atoms is in the range of 0.5–1.6, the bond connecting them is categorized as a polar covalent bond. In a polar covalent bond, the electrons are not shared equally between the atoms, and there is an uneven distribution of charge leading to partial positive and partial negative charges on the atoms. A nonpolar covalent bond usually occurs when the electronegativity difference is less than 0.5. In nonpolar covalent bonds, the electrons are shared almost equally between the atoms, resulting in a symmetrical distribution of the charge. In the presence of a metal, the bond transitions into an ionic one when the electronegativity difference between the metal and nonmetal exceeds 1.6. In an ionic bond, electrons are transferred from the less electronegative metal to the more electronegative nonmetal, resulting in the formation of ions with opposite charges.68−71 The relationship between the energy gap (Eg) and optical electronegativity (χ∗) in systems is as follows72:

3.2. 8

where (Δχ∗) represents the variation in optical electronegativity between the cation and the anion. This equation suggests that Eg is directly proportional to the value of Δχ∗, with a factor of 3.72. In the case of pure Cs2AgBiBr6, the value of Δχ∗ is given as 0.513. In the doped Cs2AgBiBr6, the value of Δχ∗ decreases to 0.48. As Δχ∗ difference is 0.03, a nonpolar covalent bond is formed as shown in Figure 3b. Covalent bonds in double perovskite solar cells are essential for enhancing the material’s structural stability. These bonds establish strong connections among the component atoms, which help maintain the integrity of the crystal structure. The presence of covalent bonds in double perovskite solar cells serves multiple purposes, including exerting influence on electronic properties, promoting efficient charge transport, and enabling engineering of the material’s attributes. All of these factors collectively enhance the photovoltaic performance of the solar cell, making it more efficient in converting sunlight into electricity.73−75

The extinction coefficient (k) is a measure of the efficiency with which a substance absorbs light at a particular wavelength. It is an intrinsic property that relies on the atomic and chemical structural composition of the isolated sequences.76 In the context of the LFHDP, k is determined using the provided mathematical equation55:

3.2. 9

where the value of “γ” is −0.32 as by calculating the value of k for pristine Cs2AgBiBr6 was 2.221, but for the doped Al, the 'k' value becomes 2.220 shown by the graph in Figure 3b. Doping with 5% Al results in a decrease in the value of 'k'. This reduction in 'k' may indicate a decrease in optical losses due to surface optical dispersion, an increase in carrier concentration, and reduced surface roughness. The optical characteristics of semiconductor materials can be described using the complex dielectric function (ε)77:

3.2. 10

where εr represents the real part, and εi stands for the imaginary component of the dielectric constant, which are represented in terms of “n' and 'k” as42,77:

3.2. 11
3.2. 12

The real part of the ε indeed demonstrates the degree to which materials polarize when exposed to electromagnetic fields or incident light. The εi value is associated with electron transitions, which rely on electron movements between the conduction and valence bands. The εi value of the dielectric function is of significant importance for any material. It functions as a connection between the microphysical mechanisms involved in interband transitions and the electronic arrangement within the solid. This facilitates a deeper understanding of the solid’s energy band structure and various spectral information. The εr and εi values of the dielectric constant increase with doping. In the undoped material, the εr and εi values are 2.62 and 12.21, respectively, while in the doped material, they rise to 2.85 and 12.39 as shown in Figure 4a,b, indicating the impact of doping on these dielectric properties. The observation that the values of the εr part are higher compared to the εi value in Al-doped Cs2AgBiBr6 films indicates an increase in the real part of the dielectric constant in these thin films due to Al doping. It may be possible that such an increase is likely a result of an enhanced electric flux density in the Cs2AgBiBr6 thin films caused by the introduction of Al. Consequently, optical conductivity is improved with Al doping, leading to increased electronic transfers through the films.61,78

Figure 4.

Figure 4

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(a) Real part of extinction coefficient εr and (b) imaginary part of extinction coefficient εi for undoped and doped Al–Cs2AgBiBr6..

3.3. J–V Curve

Using the J–V curve in Figure 5, the short-circuit current density (Jsc), fill factor (FF), open-circuit voltage (Voc), and efficiency η (%) of Cs2AgBiBr6-based solar cell and Al-doped Cs2AgBiBr6 solar cell are determined, and the calculated values are given in Table 1.

Figure 5.

Figure 5

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J–V curve of pure and Al-doped solar cell.

Table 1. Solar Cell Parameters of Pure and Al-Doped Cs2AgBiBr6.

samples Jsc (mA/cm2) Voc (V) FF efficiency (η%)
Cs2AgBiBr6 5.01 0.89 0.67 3.02
5% Al doped 5.29 0.91 0.71 3.40
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When the electrodes of a solar cell are directly linked, Jsc represents the electrical current that flows through the external circuit. A solar cell’s Jsc value is influenced by the photon flux that the incident light produces, which is established by the light’s spectral makeup. The word 'Jsc' is frequently used to refer to the highest current output that a solar cell can produce. For pure Cs2AgBiBr6, Jsc is 5.01 mA/cm2 in its undoped state and after Al doping, it increases to 5.29 mA cm–2. Numerous variables affect Jsc, such as the chance of electron collection, optical characteristics, incident light intensity, and the incident light’s spectral composition. A decrease in the bandgap is frequently linked to an increase in Jsc, which raises the material’s electron density.79−81

Voc is one of the most critical parameters in determining the PCE of organic solar cells. Voc for the doped Al is 0.91 V, while for the undoped, it becomes 0.89 V. The energy difference between the conduction band (CB) of the electron acceptor and the valence band (VB) of the electron donor is the primary source of the Voc value. In the case of Al doping, the stronger interaction between Al-3p and Ag-5s states widens the CB, causing the density of states to shift toward lower energy levels. As a result, for the Al-doped material, the Fermi level moves upward into the CB, giving rise to the formation of an n-type semiconductor and making optical transitions more accessible. This shift in the Fermi level and the easier optical transition account for the increase in the Voc value.82−84 The FF of a solar cell is calculated by dividing the maximum power output (Pmax) by Voc × Jsc(85,86):

3.3. 13

where Pmax = (Jmax × Vmax). The FF value of pure was 0.67, but after doping, its value increased to 0.71. The FF is indeed influenced by the recombination rate within a solar cell. A higher FF often indicates a reduced recombination rate, signifying a better cell performance. It is possible that the doping of Al has a role in reducing the recombination of electron–hole pairs, which in turn leads to the presence of more free electrons in the CB. This, in turn, lowers electrical resistance and increases the FF value87:

3.3. 14

To compare the performance of various solar cells, efficiency is the most frequently employed parameter. The efficiency of LFHDPs for undoped was 3.02%, and for doped, it became 3.40%, which was calculated through eq 14. This improvement in efficiency can be attributed to the increase in several key parameters, including Jsc, Voc, and FF. Due to this, LFHDP cells are more effective at converting incident light into electrical power.81,88

4. Conclusions

The perovskite solar cells using Cs2AgBiBr6 with and without Al doping were fabricated by a sol–gel spin-coating method. It was concluded that the doping of Al in Cs2AgBiBr6 effects substantially on its structural, optical, and photovoltaic properties. The structural properties were clarified from the lattice parameter, dislocation line density, crystal size, d-spacing, and the volume of particles, obtained based on the XRD pattern. In addition, the optical properties were calculated from UV–vis spectroscopy, which are bandgap, electronegativity, extinction coefficient, and dielectric constant. The peaks in the XRD were shifted, which confirms the Al presence. The increase in intensity of the peaks shows its crystallinity. The grain size was increased, and Eg decreased with Al doping. The J–V curve showed that the device performance for pristine Cs2AgBiBr6 was 5.01 mA/cm2 of Jsc, 0.89 V of Voc, 0.67 of FF, and 3.02% of the efficiency of a double perovskite solar cell. The calculated parameters for Al-doped material are extracted from the J–V graph, which revealed 5.29 mA/cm2 of Jsc, 0.91 V of Voc, and 0.71 of FF. Overall, the efficiency was increased by Al doping to 3.40% which is 12.5% greater than that of the pure Cs2AgBiBr6 thin film. It was concluded that this study not only shows a notable improvement in the solar cell performance but is the first to comprehensively describe the aforementioned properties of Cs2AgBiBr6 and Al-doped Cs2AgBiBr6 as well.

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No.: NRF-2021R1F1A1062849). This research was supported by Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2024R327), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.

The authors declare no competing financial interest.

References

  1. Qureshi F.; Yusuf M.; Kamyab H.; Vo D.-V. N.; Chelliapan S.; Joo S.-W.; Vasseghian Y. Latest eco-friendly avenues on hydrogen production towards a circular bioeconomy: Currents challenges, innovative insights, and future perspectives. Renewable and Sustainable Energy Reviews 2022, 168, 112916 10.1016/j.rser.2022.112916. [DOI] [Google Scholar]
  2. Huang Z.; Luo P.; Wu Q.; Zheng H. Constructing one-dimensional mesoporous carbon nanofibers loaded with NaTi2 (PO4) 3 nanodots as novel anodes for sodium energy storage. J. Phys. Chem. Solids 2022, 161, 110479 10.1016/j.jpcs.2021.110479. [DOI] [Google Scholar]
  3. Kumar A.; Singh S.; Mohammed M. K.; Shalan A. E. Effect of 2D perovskite layer and multivalent defect on the performance of 3D/2D bilayered perovskite solar cells through computational simulation studies. Sol. Energy 2021, 223, 193–201. 10.1016/j.solener.2021.05.042. [DOI] [Google Scholar]
  4. Al-mousoi A.; Mehde M.; Al-gebori A.. Annealing temperature effects on the performance of the perovskite solar cells. In IOP Conference Series: Materials Science and Engineering; IOP Publishing, 2020; Vol. 757, p. 012039. [Google Scholar]
  5. Correa-baena J.-P.; Saliba M.; Buonassisi T.; Grätzel M.; Abate A.; Tress W.; Hagfeldt A. Promises and challenges of perovskite solar cells. Science 2017, 358 (6364), 739–744. 10.1126/science.aam6323. [DOI] [PubMed] [Google Scholar]
  6. Ghosh S.; Shankar H.; Kar P. Recent developments of lead-free halide double perovskites: a new superstar in the optoelectronic field. Materials Advances 2022, 3 (9), 3742–3765. 10.1039/D2MA00071G. [DOI] [Google Scholar]
  7. Hu F.; Mou S.; Wei S.; Qiu L.; Hu H.; Zhou H. Research on the evolution of China’s photovoltaic technology innovation network from the perspective of patents. Energy Strategy Rev. 2024, 51, 101309 10.1016/j.esr.2024.101309. [DOI] [Google Scholar]
  8. Lei H.; Hardy D.; Gao F. Lead-free double perovskite Cs2AgBiBr6: fundamentals, applications, and perspectives. Adv. Funct. Mater. 2021, 31 (49), 2105898 10.1002/adfm.202105898. [DOI] [Google Scholar]
  9. Wang M.; Jiang C.; Zhang S.; Song X.; Tang Y.; Cheng H.-M. Reversible calcium alloying enables a practical room-temperature rechargeable calcium-ion battery with a high discharge voltage. Nature Chem. 2018, 10 (6), 667–672. 10.1038/s41557-018-0045-4. [DOI] [PubMed] [Google Scholar]
  10. Khan M.; Hussain S.; Subhani W. S.; Ammami M.; Shahid W.; Ali R. Tungsten dopant incorporation for bandgap and type engineering of perovskite crystals. Phys. Scr. 2023, 98 (9), 095517 10.1088/1402-4896/acecc1. [DOI] [Google Scholar]
  11. Bhaumik S.; Ray S.; Batabyal S. K. Recent advances of lead-free metal halide perovskite single crystals and nanocrystals: synthesis, crystal structure, optical properties, and their diverse applications. Materials today chemistry 2020, 18, 100363 10.1016/j.mtchem.2020.100363. [DOI] [Google Scholar]
  12. Kojima A.; Teshima K.; Shirai Y.; Miyasaka T. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. Journal of the American chemical society 2009, 131 (17), 6050–6051. 10.1021/ja809598r. [DOI] [PubMed] [Google Scholar]
  13. Yang W. S.; Noh J. H.; Jeon N. J.; Kim Y. C.; Ryu S.; Seo J.; Seok S. I. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange. Science 2015, 348 (6240), 1234–1237. 10.1126/science.aaa9272. [DOI] [PubMed] [Google Scholar]
  14. Karmakar A.; Dodd M. S.; Agnihotri S.; Ravera E.; Michaelis V. K. Cu (II)-doped Cs2SbAgCl6 double perovskite: A lead-free, low-bandgap material. Chem. Mater. 2018, 30 (22), 8280–8290. 10.1021/acs.chemmater.8b03755. [DOI] [Google Scholar]
  15. Li X.; Aftab S.; Abbas A.; Hussain S.; Aslam M.; Kabir F.; Abd-rabboh H. S.; Hegazy H.; Xu F.; Ansari M. Z. Advances in mixed 2D and 3D perovskite heterostructure solar cells: a comprehensive review. Nano Energy 2023, 118, 108979. 10.1016/j.nanoen.2023.108979. [DOI] [Google Scholar]
  16. Wang M.; Wang W.; Ma B.; Shen W.; Liu L.; Cao K.; Chen S.; Huang W. Lead-free perovskite materials for solar cells. Nano-Micro Lett. 2021, 13, 62. 10.1007/s40820-020-00578-z. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Mu S.; Liu Q.; Kidkhunthod P.; Zhou X.; Wang W.; Tang Y. Molecular grafting towards high-fraction active nanodots implanted in N-doped carbon for sodium dual-ion batteries. Natl. Sci. Rev. 2021, 8 (7), nwaa178 10.1093/nsr/nwaa178. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Tailor N. K.; Listorti A.; Colella S.; Satapathi S. Lead-Free Halide Double Perovskites: Fundamentals, Challenges, and Photovoltaics Applications. Adv. Mater. Technol. 2023, 8 (1), 2200442 10.1002/admt.202200442. [DOI] [Google Scholar]
  19. Kung P.-K.; Li M.-H.; Lin P.-Y.; Jhang J.-Y.; Pantaler M.; Lupascu D. C.; Grancini G.; Chen P. Lead-free double perovskites for perovskite solar cells. Solar RRL 2020, 4 (2), 1900306 10.1002/solr.201900306. [DOI] [Google Scholar]
  20. Sekar K.; Marasamy L.; Mayarambakam S.; Hawashin H.; Nour M.; Bouclé J. Lead-free, formamidinium germanium-antimony halide (FA 4 GeSbCl 12) double perovskite solar cells: the effects of band offsets. RSC Adv. 2023, 13 (36), 25483–25496. 10.1039/D3RA03102K. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Kale A. J.; Chaurasiya R.; Dixit A. Photovoltaic characteristics of ultrathin Cs2CuBiCl6 halide double perovskite based solar cell: theoretical studies. Optik 2023, 281, 170820 10.1016/j.ijleo.2023.170820. [DOI] [Google Scholar]
  22. Longo G.; Mahesh S.; Buizza L. R.; Wright A. D.; Ramadan A. J.; Abdi-jalebi M.; Nayak P. K.; Herz L. M.; Snaith H. J. Understanding the performance-limiting factors of Cs2AgBiBr6 double-perovskite solar cells. ACS Energy Letters 2020, 5 (7), 2200–2207. 10.1021/acsenergylett.0c01020. [DOI] [Google Scholar]
  23. Yadav S. C.; Srivastava A.; Manjunath V.; Kanwade A.; Devan R. S.; Shirage P. M. Properties, performance and multidimensional applications of stable lead-free Cs2AgBiBr6 double perovskite. Mater. Today Phys. 2022, 26, 100731 10.1016/j.mtphys.2022.100731. [DOI] [Google Scholar]
  24. Huang Z.; Luo P.; Jia S.; Zheng H.; Lyu Z. A sulfur-doped carbon-enhanced Na3V2 (PO4) 3 nanocomposite for sodium-ion storage. J. Phys. Chem. Solids 2022, 167, 110746 10.1016/j.jpcs.2022.110746. [DOI] [Google Scholar]
  25. Lu L.; Wu W.; Gao Y.; Pan C.; Yu X.; Zhang C.; Jin Z. Study on current discrepancy and redistribution of HTS non-insulation closed-loop coils during charging/discharging and subsequent transient process toward steady-state operation. Supercond. Sci. Technol. 2022, 35 (9), 095001 10.1088/1361-6668/ac7dfe. [DOI] [Google Scholar]
  26. Yang S.; Huang Z.; Hu Q.; Zhang Y.; Wang F.; Wang H.; Shu Y. Proportional optimization model of multiscale spherical BN for enhancing thermal conductivity. ACS Applied Electronic Materials 2022, 4 (9), 4659–4667. 10.1021/acsaelm.2c00878. [DOI] [Google Scholar]
  27. Greul E.; Petrus M. L.; Binek A.; Docampo P.; Bein T. Highly stable, phase pure Cs 2 AgBiBr 6 double perovskite thin films for optoelectronic applications. Journal of Materials Chemistry A 2017, 5 (37), 19972–19981. 10.1039/C7TA06816F. [DOI] [Google Scholar]
  28. Jiang C.; Deng Z.; Liu B.; Li J.; Han Z.; Ma Y.; Wu D.; Maeda H.; Ma Y. Spin–Orbit-Engineered Selective Transport of Photons in Plasmonic Nanocircuits with Panda-Patterned Transporters. ACS Photonics 2022, 9 (9), 3089–3093. 10.1021/acsphotonics.2c00841. [DOI] [Google Scholar]
  29. Pantaler M.; Olthof S.; Meerholz K.; Lupascu D. C. Bismuth-Antimony mixed double perovskites Cs2AgBi1-xSbxBr6 in solar cells. MRS Advances 2019, 4 (64), 3545–3552. 10.1557/adv.2019.404. [DOI] [Google Scholar]
  30. Huang Z.; Zhang Y.; Wang H.; Li J. Improved electrical resistivity-temperature characteristics of oriented hBN composites for inhibiting temperature-dependence DC surface breakdown. Appl. Phys. Lett. 2023, 123, 103501. 10.1063/5.0166638. [DOI] [Google Scholar]
  31. Zhang Y.; Liu X.; Song M.; Qin Z. Tuning the Red-to-Green-Upconversion Luminescence Intensity Ratio of Na3ScF6:20% Yb3+, 2% Er3+ Particles by Changes in Size. Materials 2023, 16 (6), 2247. 10.3390/ma16062247. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Azizah N. m.; Muhammady S.; Purbayanto M. A. K.; Nurfani E.; Winata T.; Sustini E.; Widita R.; Darma Y. Influence of Al doping on the crystal structure, optical properties, and photodetecting performance of ZnO film. Progress in Natural Science: Materials International 2020, 30 (1), 28–34. 10.1016/j.pnsc.2020.01.006. [DOI] [Google Scholar]
  33. Khlayboonme S. T.; Thowladda W. Impact of Al-doping on structural, electrical, and optical properties of sol-gel dip coated ZnO: Al thin films. Materials Research Express 2021, 8 (7), 076402 10.1088/2053-1591/ac113d. [DOI] [Google Scholar]
  34. Mishra P. N.; Mishra P. K.; Pathak D. The influence of Al doping on the optical characteristics of ZnO nanopowders obtained by the low-cost sol-gel method. Chemistry 2022, 4 (4), 1136–1146. 10.3390/chemistry4040077. [DOI] [Google Scholar]
  35. Wai H. S.; Li C. Effect of aluminum doping ratios on the properties of aluminum-doped zinc oxide films deposited by mist chemical vapor deposition method applying for photocatalysis. Nanomaterials 2022, 12 (2), 195. 10.3390/nano12020195. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Zhang X.; Tang Y.; Zhang F.; Lee C.-S. A novel aluminum–graphite dual-ion battery. Adv. Energy Mater. 2016, 6 (11), 1502588 10.1002/aenm.201502588. [DOI] [Google Scholar]
  37. El-henawey M.; Hossain I. M.; Zhang L.; Bagheri B.; Kottokkaran R.; Dalal V. L. Influence of grain size on the photo-stability of perovskite solar cells. Journal of Materials Science: Materials in Electronics 2021, 32, 4067–4075. 10.1007/s10854-020-05148-y. [DOI] [Google Scholar]
  38. Adnan M.; Usman M.; Ali S.; Javed S.; Islam M.; Akram M. A. Aluminum Doping Effects on Interface Depletion Width of Low Temperature Processed ZnO Electron Transport Layer-Based Perovskite Solar Cells. Frontiers in Chemistry 2022, 9, 795291 10.3389/fchem.2021.795291. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Kruszyńska J.; Ostapko J.; Ozkaya V.; Surucu B.; Szawcow O.; Nikiforow K.; Hołdyński M.; Tavakoli M. M.; Yadav P.; Kot M. Atomic Layer Engineering of Aluminum-Doped Zinc Oxide Films for Efficient and Stable Perovskite Solar Cells. Adv. Mater. Interfaces 2022, 9 (17), 2200575 10.1002/admi.202200575. [DOI] [Google Scholar]
  40. Murgulov V.; Schweinle C.; Daub M.; Hillebrecht H.; Fiederle M.; Dědič V.; Franc J. Double perovskite Cs 2 AgBiBr 6 radiation sensor: synthesis and characterization of single crystals. J. Mater. Sci. 2022, 57, 2758–2774. 10.1007/s10853-021-06847-5. [DOI] [Google Scholar]
  41. Abdelsamie M.; Cruse K.; Tamura N.; Ceder G.; Sutter-fella C. M. Impact of processing conditions on the film formation of lead-free halide double perovskite Cs 2 AgBiBr 6. Journal of Materials Chemistry A 2022, 10 (37), 19868–19880. 10.1039/D2TA00763K. [DOI] [Google Scholar]
  42. Khan M.; Bhatti K.; Qindeel R.; Althobaiti H. S.; Alonizan N. Structural, electrical and optical properties of multilayer TiO2 thin films deposited by sol–gel spin coating. Results in physics 2017, 7, 1437–1439. 10.1016/j.rinp.2017.03.023. [DOI] [Google Scholar]
  43. Khan M. I.; Yasmin S.; Alwadai N.; Irfan M.; Albalawi H.; Almuqrin A. H.; Almoneef M. M.; Iqbal M. Bi and Sn Doping Improved the Structural, Optical and Photovoltaic Properties of MAPbI3-Based Perovskite Solar Cells. Materials 2022, 15 (15), 5216. 10.3390/ma15155216. [DOI] [PMC free article] [PubMed] [Google Scholar] [Retracted]
  44. Fang F.; Li H.; Fang S.; Zhou B.; Huang F.; Ma C.; Wan Y.; Jiang S.; Wang Y.; Tian B. 2D Cs2AgBiBr6 with Boosted Light–Matter Interaction for High-Performance Photodetectors. Adv. Opt. Mater. 2021, 9 (9), 2001930 10.1002/adom.202001930. [DOI] [Google Scholar]
  45. Sharma N.; Kumar S. Effect of Ag Doping on Properties of Al–Doped ZnO Nanoparticles Varies as Zn1-X-YAgxALYO. Mater. Sci. Res. India 2017, 14, 146. 10.13005/msri/140210. [DOI] [Google Scholar]
  46. Khan M.; Shehzad A.; Farooq W.; Arfan M.; Hasan M.; Atif M.; Hanif A. 900 keV Au ions implantation effect on the efficiency of dye sensitized solar cells. Results Phys. 2019, 14, 102425 10.1016/j.rinp.2019.102425. [DOI] [Google Scholar]
  47. Bano S.; Khan M.; Albalawi H.; Ul islam G.; Siddique M.; Ahmad T.; Alkhaldi H.; Ahson R.; Hussain S. Effect of Cd doping on the structural, optical, and photovoltaic properties of SnS films. J. Mater. Res. Technol. 2022, 19, 1982–1992. 10.1016/j.jmrt.2022.05.137. [DOI] [Google Scholar]
  48. Sivakumar P.; Akkera H. S.; Reddy T. R. K.; Bitla Y.; Ganesh V.; Kumar P. M.; Reddy G. S.; Poloju M. Effect of Ti doping on structural, optical and electrical properties of SnO2 transparent conducting thin films deposited by sol-gel spin coating. Opt. Mater. 2021, 113, 110845 10.1016/j.optmat.2021.110845. [DOI] [Google Scholar]
  49. Hussain S.; Alwadai N.; Khan M. I.; Irfan M.; Albalawi H.; Almuqrin A. H.; Almoneef M. M.; Iqbal M. The effect of 600 keV Ag ion irradiation on the structural, optical, and photovoltaic properties of MAPbBr3 films for perovksite solar cell applications. Materials 2022, 15 (15), 5299. 10.3390/ma15155299. [DOI] [PMC free article] [PubMed] [Google Scholar] [Retracted]
  50. Alsaad A. M.; Ahmad A. A.; Al-bataineh Q. M.; Bani-salameh A. A.; Abdullah H. S.; Qattan I. A.; Albataineh Z. M.; Telfah A. D. Optical, structural, and crystal defects characterizations of dip synthesized (Fe-Ni) Co-doped ZnO thin films. Materials 2020, 13 (7), 1737. 10.3390/ma13071737. [DOI] [PMC free article] [PubMed] [Google Scholar]
  51. Amroun M.; Salim K.; Kacha A.; Khadraoui M. Effect of TM (TM= Sn, Mn, Al) doping on the physical properties of ZnO thin films grown by spray pyrolysis technique: a comparative study. Int. J. Thin. Film. Sci. Technol. 2020, 9 (1), 7–19. 10.18576/ijtfst/090102. [DOI] [Google Scholar]
  52. Haq I.; Khan M.; Irfan M.; Fatima M.; Somaily H.; Elqahtani Z. M.; Alwadai N. Increase the current density and reduce the defects of ZnO by modification of the band gap edges with Cu ions implantation for efficient, flexible dye-sensitized solar cells (FDSSCs). Ceram. Int. 2023, 49, 29622. 10.1016/j.ceramint.2023.06.188. [DOI] [Google Scholar]
  53. Burns A.; Hayes G.; Li W.; Hirvonen J.; Demaree J. D.; Shah S. I. Neodymium ion dopant effects on the phase transformation in sol–gel derived titania nanostructures. Materials Science and Engineering: B 2004, 111 (2–3), 150–155. 10.1016/j.mseb.2004.04.008. [DOI] [Google Scholar]
  54. Thawarkar S.; Rondiya S. R.; Dzade N. Y.; Khupse N.; Jadkar S. Experimental and Theoretical Investigation of the Structural and Opto-electronic Properties of Fe-Doped Lead-Free Cs2AgBiCl6 Double Perovskite. Chemistry–A. European Journal 2021, 27 (26), 7408–7417. 10.1002/chem.202004902. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Khan M. I.; Mukhtar A.; Alwadai N.; Irfan M.; Haq I.-U.; Albalawi H.; Almuqrin A. H.; Almoneef M. M.; Iqbal M. Improving the structural, optical and photovoltaic properties of Sb-and Bi-Co-doped MAPbBr3 perovskite solar cell. Coatings 2022, 12 (3), 386. 10.3390/coatings12030386. [DOI] [Google Scholar]
  56. Khan M.; Ali S.; Alwadai N.; Irfan M.; Albalawi H.; Almuqrin A. H.; Almoneef M. M.; Iqbal M. Structural, electrical and optical properties of hetrostructured MoS2/ZnO thin films for potential perovskite solar cells application. J. Mater. Res. Technol. 2022, 20, 1616–1623. 10.1016/j.jmrt.2022.07.082. [DOI] [Google Scholar]
  57. Yang J.; Zhang P.; Wei S.-H. Band structure engineering of Cs2AgBiBr6 perovskite through order–disordered transition: A first-principle study. journal of physical chemistry letters 2018, 9 (1), 31–35. 10.1021/acs.jpclett.7b02992. [DOI] [PubMed] [Google Scholar]
  58. Zheng X.; Colegrove E.; Duenow J.; Moseley J.; Metzger W. Roles of bandgrading, lifetime, band alignment, and carrier concentration in high-efficiency CdSeTe solar cells. J. Appl. Phys. 2020, 128 (5), 053102 10.1063/5.0013726. [DOI] [Google Scholar]
  59. Guo H.; Meng R.; Wang G.; Wang S.; Wu L.; Li J.; Wang Z.; Dong J.; Hao X.; Zhang Y. Band-gap-graded Cu 2 ZnSn (S, Se) 4 drives highly efficient solar cells. Energy Environ. Sci. 2022, 15 (2), 693–704. 10.1039/D1EE03134A. [DOI] [Google Scholar]
  60. Khan M.; Farooq W.; Saleem M.; Bhatti K.; Atif M.; Hanif A. Phase change, band gap energy and electrical resistivity of Mg doped TiO2 multilayer thin films for dye sensitized solar cells applications. Ceram. Int. 2019, 45 (17), 21436–21439. 10.1016/j.ceramint.2019.07.133. [DOI] [Google Scholar]
  61. Chen H.; Qu Y.; Sun L.; Peng J.; Ding J. Band structures and optical properties of Ag and Al co-doped ZnO by experimental and theoretic calculation. Physica E: Low-dimensional Systems and Nanostructures 2019, 114, 113602 10.1016/j.physe.2019.113602. [DOI] [Google Scholar]
  62. Feng X.; Sun L.; Wang W.; Zhao Y.; Shi J.-W. Construction of CdS@ ZnO core–shell nanorod arrays by atomic layer deposition for efficient photoelectrochemical H2 evolution. Sep. Purif. Technol. 2023, 324, 124520 10.1016/j.seppur.2023.124520. [DOI] [Google Scholar]
  63. Hadia N.; Mohamed H. A.-H. Characteristics and optical properties of MgO nanowires synthesized by solvothermal method. Materials Science in Semiconductor Processing 2015, 29, 238–244. 10.1016/j.mssp.2014.03.049. [DOI] [Google Scholar]
  64. Ravindra N.; Ganapathy P.; Choi J. Energy gap–refractive index relations in semiconductors–An overview. Infrared physics & technology 2007, 50 (1), 21–29. 10.1016/j.infrared.2006.04.001. [DOI] [Google Scholar]
  65. Khan M.; Naeem M.; Mustafa G. M.; Abubshait S. A.; Mahmood A.; Al-masry W.; Al-garadi N. Y.; Ramay S. M. Synthesis and characterization of Co and Ga co-doped ZnO thin films as an electrode for dye sensitized solar cells. Ceram. Int. 2020, 46 (17), 26590–26597. 10.1016/j.ceramint.2020.07.127. [DOI] [Google Scholar]
  66. Ali M. A.; Alshgari R. A.; Awadh bahajjaj A. A.; Sillanpää M. The study of new double perovskites K2AgAsX6 (X= Cl, Br) for energy-based applications. J. Taibah Univ. Sci. 2023, 17 (1), 2170680 10.1080/16583655.2023.2170680. [DOI] [Google Scholar]
  67. Sta I.; Jlassi M.; Hajji M.; Boujmil M.; Jerbi R.; Kandyla M.; Kompitsas M.; Ezzaouia H. Structural and optical properties of TiO 2 thin films prepared by spin coating. J. Sol-Gel Sci. Technol. 2014, 72, 421–427. 10.1007/s10971-014-3452-z. [DOI] [Google Scholar]
  68. Hinze J.; Jaffe H. H.; Electronegativity I. Electronegativity. I. Orbital electronegativity of neutral atoms. J. Am. Chem. Soc. 1962, 84 (4), 540–546. 10.1021/ja00863a008. [DOI] [Google Scholar]
  69. Reddy R.; Ahammed Y. N.; Gopal K. R.; Azeem P. A.; Rao T.; Reddy P. M. Optical electronegativity, bulk modulus and electronic polarizability of materials. Opt. Mater. 2000, 14 (4), 355–358. 10.1016/S0925-3467(00)00004-5. [DOI] [Google Scholar]
  70. Huang Q.-M.; Hu C.-L.; Yang B.-P.; Tang R.-L.; Chen J.; Fang Z.; Li B.; Mao J.-G. Ba2 [MoO3 (OH)(IO3) 2] IO3: a promising SHG material featuring a Λ-shaped functional motif achieved by universal mono-site substitution. Chem. Mater. 2020, 32 (15), 6780–6787. 10.1021/acs.chemmater.0c02657. [DOI] [Google Scholar]
  71. Agarwal A.; Pettersson F.; Singh A.; Kong C. S.; Saxen H.; Rajan K.; Iwata S.; Chakraborti N. Identification and optimization of AB2 phases using principal component analysis, evolutionary neural nets, and multiobjective genetic algorithms. Materials and Manufacturing Processes 2009, 24 (3), 274–281. 10.1080/10426910802678321. [DOI] [Google Scholar]
  72. Reddy R.; Gopal K. R.; Narasimhulu K.; Reddy L. S. S.; Kumar K. R.; Reddy C. K.; Ahmed S. N. Correlation between optical electronegativity and refractive index of ternary chalcopyrites, semiconductors, insulators, oxides and alkali halides. Opt. Mater. 2008, 31 (2), 209–212. 10.1016/j.optmat.2008.03.010. [DOI] [Google Scholar]
  73. Pan S.; Zhang Y.; Teng X.; Li G.; Li L. Optical properties of nitrogen-doped SnO2 films: Effect of the electronegativity on refractive index and band gap. J. Appl. Phys. 2008, 103 (9), 093103 10.1063/1.2908197. [DOI] [Google Scholar]
  74. Liu K.; Rafique S.; Musolino S. F.; Cai Z.; Liu F.; Li X.; Yuan Y.; Bao Q.; Yang Y.; Chu J. Covalent bonding strategy to enable non-volatile organic cation perovskite for highly stable and efficient solar cells. Joule 2023, 7 (5), 1033–1050. 10.1016/j.joule.2023.03.019. [DOI] [Google Scholar]
  75. Luo Z.-Z.; Cai S.; Hao S.; Bailey T. P.; Luo Y.; Luo W.; Yu Y.; Uher C.; Wolverton C.; Dravid V. P. Extraordinary role of Zn in enhancing thermoelectric performance of Ga-doped n-type PbTe. Energy Environ. Sci. 2022, 15 (1), 368–375. 10.1039/D1EE02986J. [DOI] [Google Scholar]
  76. Ubi G. M.; Ikpeme E. V.; Essien I. S.. Essentials of the COVID-19 coronavirus. In Data Science for COVID-19; Elsevier, 2022; pp. 1–25. [Google Scholar]
  77. Kanwal S.; Khan M.; Uzair M.; Fatima M.; Bukhari M.; Saman Z.; Elsaeedy H.; Shahzad U.; Elqahtani Z. M.; Alwadai N. A facile green approach to the synthesis of Bi2WO6@ V2O5 heterostructure and their photocatalytic activity evaluation under visible light irradiation for RhB dye removal. Arab. J. Chem. 2023, 16 (5), 104685 10.1016/j.arabjc.2023.104685. [DOI] [Google Scholar]
  78. Nion M. G. M.; Kabir M. H.; Mona M. A.; Haque M. J.; Shahariar N.; Hafiz M.; Rahman M. Effect of Al doping on morphology and optical properties of spray pyrolized MgO thin films. Results Mater. 2021, 12, 100235 10.1016/j.rinma.2021.100235. [DOI] [Google Scholar]
  79. Roudgar-amoli M.; Shariatinia Z. Dye-sensitized solar cells with efficiencies exceeding 10% engineered based on La2MnTiO6 double perovskite and MOF-derived Cr2O3/C nanocomposites in bi-layered photoanodes. Opt. Mater. 2023, 145, 114456 10.1016/j.optmat.2023.114456. [DOI] [Google Scholar]
  80. Koster L. J. A.Device physics of donor/acceptor-blend solar cells, 2007.
  81. Singh K. J.; Sarkar S. K. Highly efficient ARC less InGaP/GaAs DJ solar cell numerical modeling using optimized InAlGaP BSF layers. Optical and Quantum Electronics 2012, 43, 1–21. 10.1007/s11082-011-9499-y. [DOI] [Google Scholar]
  82. Shintaku N.; Hiramoto M.; Izawa S. Doping for controlling open-circuit voltage in organic solar cells. J. Phys. Chem. C 2018, 122 (10), 5248–5253. 10.1021/acs.jpcc.7b12203. [DOI] [PubMed] [Google Scholar]
  83. Suo Z.; Dai J.; Gao S.; Gao H. Effect of transition metals (Sc, Ti, V, Cr and Mn) doping on electronic structure and optical properties of CdS. Results in Physics 2020, 17, 103058 10.1016/j.rinp.2020.103058. [DOI] [Google Scholar]
  84. Li X.; Aftab S.; Hussain S.; Kabir F.; Henaish A.; Al-sehemi A. G. Dimensional Diversity (0D, 1D, 2D, 3D) in Perovskite Solar Cells: Exploring the Potential of Mix-dimensional Integrations. J. Mater. Chem. A 2024, 12, 4421. 10.1039/D3TA06953B. [DOI] [Google Scholar]
  85. Attia A.; Hussain S.; Khan M.; Sadaf A.; Seliem A. F.; Mohammed A. Y.; Ibrahim M. M. Tuning the band gap edges of perovskite material by Cd doping for achieving high current density in perovskite solar cells. Ceram. Int. 2023, 49 (12), 20465–20469. 10.1016/j.ceramint.2023.03.176. [DOI] [Google Scholar]
  86. Hussain S.; Khan M.; Ghafoor A.; Subhani W. S.; Shahid W.; Mahmoud Z.; Elqahtani Z. M.; Ercan F.; Alwadai N.; Iqbal M. Understanding the influence of Cu ions implantation towards highly efficient MAPbBr3 perovskite solar cells. Opt. Mater. 2023, 140, 113806 10.1016/j.optmat.2023.113806. [DOI] [Google Scholar]
  87. Shahedi Z.; Jafari M. R. Synthesis Al complex and investigating effect of doped ZnO nanoparticles in the electrical and optical efficiency of OLEDS. Appl. Phys. A: Mater. Sci. Process. 2017, 123, 98. 10.1007/s00339-016-0715-2. [DOI] [Google Scholar]
  88. Amjad M.; Khan M. I.; Alwadai N.; Irfan M.; Albalawi H.; Almuqrin A. H.; Almoneef M. M.; Iqbal M. Photovoltaic properties of ZnO films Co-doped with Mn and La to enhance solar cell efficiency. Nanomaterials 2022, 12 (7), 1057. 10.3390/nano12071057. [DOI] [PMC free article] [PubMed] [Google Scholar]

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