Enhancing structural and optical properties of hybrid perovskite layers with polymer modification

Abstract

Incorporating polymer additives into hybrid perovskite solar cells is an effective strategy to enhance stability while retaining high efficiency. This study examines the impact of three polymers: polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and polyvinyl alcohol (PVA) added at varying concentrations on the stability of perovskite as the absorber layer. Structural, optical, and electrochemical analyses demonstrate that adding PEG 0.3 mg/ml significantly improves perovskite films’ morphology, light absorption, and charge transport while reducing recombination losses and enhancing long-term stability. Specifically, at room temperature and 30% relative humidity, the optimized perovskite sample with 0.3 mg/mL PEG maintained stability for up to 1000 h. Additionally, The UV analysis determined the band gap to be 1.58 eV. The electrochemical impedance spectroscopy analysis evaluated the charge transfer resistance (Rct) to be 1408 Ωcm², lower than other samples modified with polymer. The findings reveal that polymer modification significantly enhances the stability and efficiency of perovskite solar cells, improving their reliability and market competitiveness.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-026-36719-4.

Introduction

Perovskite solar cells (PSCs) represent a revolutionary advancement in solar energy technology, achieving remarkable efficiencies while offering the potential for cost-effective and scalable manufacturing¹. Hybrid perovskites, particularly those with the ABX3 formula (where A is an organic cation like methylammonium (MA) or formamidinium (FA), B is a metal cation such as lead (Pb). X is a halide anion like iodine (I), bromine (Br), or chlorine (Cl)), exhibit excellent light-absorbing capabilities and significant power conversion efficiencies (PCEs)^2,3. A major hurdle in developing hybrid perovskite technology is their limited long-term stability when exposed to environmental factors, primarily due to their sensitivity to moisture and oxygen^4,5.

In response, researchers have been actively pursuing various solutions, with the integration of polymer additives into the perovskite absorbing layer emerging as a particularly effective strategy^6,7. In perovskite solar cells (PSCs), polymers can act to optimize various aspects of the device, including film morphology, defect density, mechanical strength, and resistance to environmental influences. The incorporating polymers into perovskite leads to both improved performance and increased lifespan⁸.

Hybrid perovskites have attracted significant interest as photovoltaic materials due to their outstanding optoelectronic properties, notably their high light absorption capacity, adjustable band gaps, and extended carrier diffusion lengths⁹. These attributes facilitate efficient light harvesting and charge transport, both essential for achieving high-performing solar cells. However, a significant limitation of hybrid perovskites is their intrinsic instability, particularly under humid conditions. Exposure to moisture leads to accelerated decomposition of the perovskite structure, resulting in diminished performance and shortened operational lifetime¹⁰. This degradation primarily stems from the solubilization of the organic components and the subsequent collapse of the perovskite lattice^11,12.

To address the stability issues mentioned earlier, researchers have added polymer additives to hybrid perovskite mixtures¹³. Incorporating polymers enhances the physical robustness of perovskite films by fostering uniform, defect-free layers. This uniformity decreases grain boundaries and trap sites, improving charge carrier mobility and reducing recombination losses¹⁴. Additionally, polymers can provide a hydrophobic barrier, protecting the perovskite material from moisture and oxygen^15,16. For example, PEG, PVP, and PVA are known for their hydrophilic properties, which might seem counterintuitive; however, when used in small amounts, they can improve film formation and quality, surface coverage, morphology, and defect reduction^17,18.

Current research has shown the beneficial impact of intentionally adding polymeric materials to enhance the stability and performance of PSCs^19,20. For example, improved film structure has been achieved by mixing perovskite precursors with polymers, resulting in more robust and efficient devices²¹. Additionally, polymers can act as passivation layers, reducing surface defects and preventing ion migration, which also contributes to the degradation of PSCs²².

In 2020, Zhao et al. synthesized and investigated a solar cell with a hybrid perovskite absorber layer with different ratios of MA and Cs in Cs_xMA_(1−x) PbI₃. The results showed that cesium increases the stability and efficiency of the perovskite absorbent layer. So, the highest yield was reported for Cs_0.1MA_0.9PbI₃ perovskite, with a value of 16.84%, which is about a 2.57% increase compared to the yield of MAPbI₃ (14.28%)²³.

In 2020, Yang et al. studied the effects of cesium in the Cs_xMA_(1−x) PbI₃ absorber layer. When X is between 0.1 and 0.3, the cesium ion replaces a fraction of the methylammonium ion without altering the MAPbI₃ perovskite crystal structure. The best performance corresponds to the state of Cs_0.1MA_0.9PbI₃ with an efficiency of 11.55%. The results indicate that perovskite solar cells (PSCs) utilizing a minimal amount of cesium doping from Cs_xMA_(1−x) PbI₃ films show the benefits of enhanced efficiency and stability of perovskite solar cells (PSCs)²⁴.

In 2017, Zou et al. synthesized a solar cell with MAPbI₃ perovskite absorber layer modified with PVP, PAA, and b-PEI polymers to improve the performance and stability of the cell, and the PVP group showed the highest efficiency and increased the efficiency from 16.9 to 18.8%. It also increased sol stability by 20 times up to 90 days by maintaining 85% of the initial efficiency compared to perovskite without polymer with a shelf life of up to 4 days with 85% decomposition²⁵.

2016 Zhao et al. synthesized a PEG self-healing hygroscopic scaffold for MAPbI₃ perovskite in a solar cell. The unencapsulated cell maintains its efficiency (16%) for 300 h with a relative humidity of 70%. The findings suggest that the polymer PEG increases the stability of the perovskite film against moisture²⁶.

In 2021, Li et al. synthesized solar cells with a MAPbI3 perovskite absorber layer and PVA, PAA, and PMA additives. They reported the best efficiency related to the PAA polymer as 20.29% with an open circuit voltage of 1.13 volts. Using polymers reduces ionic migration and erosion with water and oxygen and reduces defect density. Cell efficiency without encapsulation is maintained up to 80% and 78%, respectively, up to 1000 h with illumination in the nitrogen atmosphere and 120 h in the air atmosphere²⁷.

Most previous works have examined the additives on perovskite MAPbI3. This project’s innovation is the effect of polymers PEG, PVA, and PVP in hybrid perovskite of cesium and methylammonium to enhance the stability of perovskite film. The optimal amounts of cesium with the highest efficiency have been selected X = 0.1 from the literature review paper (CsxMA1-xPbI3)^23,24.

This study aims to synthesize an organic-inorganic hybrid absorbent layer that is stable at ambient temperature. For this purpose, Cs0.1MA0.9PbI3 perovskite with additives of polyethylene glycol, polyvinyl pyrrolidone, and polyvinyl alcohol polymers with different concentrations are synthesized and deposited on FTO glass. The address layer will increase the quality of the film, its morphology, and, finally, its stability.

Materials and methods

Experimental design

First, the FTO glass is washed, and the weighing material and perovskite solution are prepared and deposited on it with a spin coater. Then, annealing is done on a hot plate.

Materials

The fluorine-doped tin oxide (FTO) coated glasses (15 Ω.cm²) were purchased from Dyesol Ltd. Methyl ammonium iodide (MAI) was purchased from Greatcell, Lead iodide (PbI₂), cesium iodide (CsI), PVP 1,300,000((C6H9NO)_n) and Lithium perchlorate (LiClO4) assay 99.99% were purchased Sigma Aldrich. Isopropanol (IPA), ethanol, HCl, Dimethyl sulfoxide (DMSO), Dimethylformamide (DMF), PEG 20,000(HO(C2H4O)_nH), PVA 72,000 ((C2H4O)_n) and Acetone were provided from Merck and used without further purifications.

Methods

First, glass slides coated with fluorine-doped tin oxide (FTO) were cleaned by ultrasonically immersing them in acetone, followed by absolute ethanol and distilled water.

Fabrication of hybrid perovskite Cs0.1MA0.9PbI3

The one-step spin coating method was used for perovskite deposition on FTO glass²⁸. To prepare a one molar methylammonium-cesium lead iodide solution are needed 244 mg of lead iodide, 76 mg of methyl ammonium iodide, and 14 mg of cesium iodide; first, weigh the mentioned ingredients. Then, dissolve them in 400 µl of dimethylformamide DMF and 100 µl of dimethyl sulfoxide DMSO at a ratio 4:1. Stir the solution for 1 h using a magnetic stirrer until it becomes uniform and transparent. The precursors are well dissolved, and PEG, PVA, and PVP additives with a concentration of 0.15, 0.3, and 0.6 mg/ml are added to the perovskite solution and stirred for 30 min at a temperature of 100–130 with a magnetic stirrer.

According to (Fig. 1), the deposition layer is performed on the FTO glass with a spin coater device at 6000 rpm for 30 s. Then, annealing is done at 60–80 C° on a hot plate for 20 min. The device has an active area of 1 cm².

Fig. 1.

The schematic illustrates the one-step spin-coating method used for perovskite film deposition.

The polymer chains of PVA, PEG, and PVP in the hybrid perovskite halide Cs0.1MA0.9PbI3 matrix deposited on FTO glass are shown in (Fig. 2). Hydroxyl (-OH) groups in PEG and PVA help in hydrogen bonding with perovskites, improving film quality and moisture resistance. Pyrrolidone (-C = O and -N-) groups in PVP interact with perovskite precursors, stabilizing the structure and reducing defects.

Fig. 2.

The PVA, PEG, and PVP polymers are incorporated into the halide perovskite matrix.

Material characterization

The morphologies and elemental distribution of the samples were analyzed using a field emission scanning electron microscope (FE-SEM) (FESEM, MIRA3 FEG-SEM, Tescan, Czech Republic) and for surface roughness of films were analysed using Atomic Force Microscope (AFM, Nanosurf AG, Switzerland) in Tapping (phase contrast) mode. The crystal structures and phase composition were examined by X-ray diffraction (XRD) using a (Tongda TD-3700, China) with Cu Kα radiation (λ = 1.5406 Å). Additional structural information was obtained through Raman spectroscopy (Renishaw Invia Raman microscope). UV–vis absorption and photoluminescence (PL) properties were investigated using a UV–vis spectrophotometer (PG Instruments, Ltd) and a PL spectrophotometer (PerkinElmer LS45) with an excitation at 470 nm for FTO/perovskite samples, respectively.

Electrochemical measurement

The electrochemical properties of perovskite film were evaluated using a dual-electrode system at room temperature. The perovskite film was applied to FTO glass as the working electrode. Measurements included cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and cyclic stability tests, all conducted using an Auto lab PGSTAT30 Potentiostat-Galvanostat. EIS data fitting and analysis were performed with ZView^® for Windows software, version 3.1 (Scribner Associates Inc., USA) available at https://www.scribner.com/software/zview.

Results and discussion

Figure 3 illustrates the UV-visible absorption spectra of Cs0.1MA0.9PbI3 films modified with PVP, PEG, and PVA polymers at concentrations of 0.15, 0.3, and 0.6, respectively, deposited on an FTO glass substrate. The data indicate that all polymer-modified samples exhibit a significantly higher absorption intensity than pure halide perovskite. This enhancement indicates that the incorporation of these polymers greatly improves the optical characteristics of the perovskite films.

Fig. 3.

The UV–vis absorption spectra of halide perovskites incorporated with PVA, PEG, and PVP polymers were analyzed to study their optical properties.

Notably, the film containing PVA at a concentration of 0.15 among the modified samples the highest absorption intensity. In contrast, the PEG-modified sample at the same concentration exhibited the lowest—the Tauc’s plot presented in (Fig. 4). Confirms that the band gap values for all samples remain consistently around 1.58 eV. This finding indicates that the introduction of polymers did not significantly modify the band gap of the perovskite, a result in line with previous studies²⁹. While the band gap remained unchanged, the polymers significantly enhanced the absorption intensity compared to the pure perovskite. The strong agreement between our calculated band gap for pure Cs_0.1MA_0.9PbI₃ and both experimental measurements and DFT calculations bolsters the confidence in our conclusions³⁰.

Fig. 4.

Tauc’s plot is used to determine the direct band gap of halide perovskites modified by polymers.

The observed improvement in light absorption properties is primarily attributed to the increased compactness, crystallinity, and uniformity of the perovskite films facilitated by adding polymer blends. These enhancements are confirmed by the X-ray diffraction (XRD) and scanning electron microscopy (SEM) results in (Fig. 7 and Fig. 10), respectively.

Fig. 7.

XRD pattern of thin film halide perovskites on FTO glass.

Fig. 10.

FESEM images of (a) Cs0.1MA0.9PbI3 perovskite. (b) Cs0.1MA0.9PbI3 perovskite with PVP 0.3 mg/ml. (c) Cs0.1MA0.9PbI3 perovskite with PEG 0.3 mg/ml. (d) Cs0.1MA0.9PbI3 perovskite with PVA 0.3 mg/ml. (e) Cross section of Cs0.1MA0.9PbI3 perovskite with PEG 0.3 mg/ml.

Incorporating polymers into Cs_0.1MA_0.9PbI₃ films retains the desirable band gap characteristics and significantly boosts their optical absorption, contributing to enhanced performance for potential applications in optoelectronic devices.

Room temperature photoluminescence (PL) spectra were employed to investigate the influence of polymer modifications (PVP, PEG, and PVA) at varying concentrations on the quality of the perovskite films, as illustrated in (Fig. 5). All films were deposited on FTO glass substrates without any charge transport layers and excited at a wavelength of 470 nm. Notably, the emission wavelengths of all films consistently centered around 700 nm, indicating that the fundamental emission properties of the perovskite were retained.

Fig. 5.

The photoluminescence spectra of halide perovskites with polymers were recorded under an excitation wavelength of 470 nm.

Some perovskite films incorporating polymer additives exhibited PL emissions with significantly higher intensities than the pure sample. This increase in PL intensity suggests enhanced radiative recombination of electron-hole pairs, reduced trap density, and better material quality. For instance, the film modified with 0.6 mg/mL PVA exhibited the highest PL intensity, indicating improved crystallinity and reduced non-radiative recombination. Conversely, the film modified with 0.6 mg/mL PVP demonstrated the lowest PL intensity, which implies a higher density of trap states and increased non-radiative recombination. As corroborated by previous studies, materials with high PL intensity are expected to improve solar cells’ photovoltaic performance³¹. Since the measurements were conducted on bare perovskite films without electron or hole transport layers, the variations in PL intensity cannot be attributed to carrier extraction effects. Instead, they reflect intrinsic changes in film quality and defect density due to the polymer additives. These interpretations are further supported by SEM results shown in (Fig. 10). The SEM images illustrate that the samples modified with 0.3 mg/ml PVP (Fig. 10b) exhibit a more uniform morphology, characterized by larger grains and more distinct grain boundaries when compared to the control sample (Fig. 10a). This morphological enhancement indicates a reduction in structural defects, aligning with the increased PL intensity and presumed longer carrier lifetimes. These morphological characteristics are directly linked to the decreased density of defects at the grain boundaries, resulting in enhanced optical properties. In contrast, (Fig. 10d) shows that the samples modified with 0.3 mg/ml PVA display more structural defects, including cracks, which correlates with lower PL intensity and diminished film quality compared to the control sample.

The optimal concentration must be carefully managed while incorporating specific polymers into the Cs_0.1MA_0.9PbI₃ matrix to enhance photoluminescent properties. Excessive addition of certain polymers, such as PVA at higher concentrations, can lead to increased recombination rates that are less desirable for photovoltaic applications. In contrast, using PVP indicates a favorable balance between film quality and optical performance, suggesting promising pathways for optimizing perovskite films.

The Raman spectra of Cs_0.1MA_0.9PbI₃, mixed with PVA, PEG, and PVP polymers on FTO glass, were recorded using a scan window ranging from 65 to 300 cm − 1, as shown in (Fig. 6). The peaks that signify the decomposition of MAPbI3 have been previously documented at 94 and 220 cm − 1³². In our measurements, we observe two peaks for Cs_0.1MA_0.9PbI₃ at 95.9 cm − 1 and 172.4 cm − 1. Cs_0.1MA_0.9PbI₃ at room temperature exhibits a tetragonal structure. Incorporating the Cs ion (0.1) in MAPbI3 enhances the rigidity of the structure due to the alteration in the ionic size of the Cs ion. Asymmetric stretching and bending modes of Pb − I can be detected in the 90 to 100 cm − 1 range. Peaks in the 140 to 400 cm^− 1 range are attributed to stretching, wagging, and asymmetric stretching modes of MA − MA^33,34. The vibrational characteristics of the PbI₆ octahedral framework are detected at frequencies below 250 cm⁻¹, with the symmetric stretching modes occurring around 95.9 cm⁻¹. Additionally, peaks in the 100 to 200 cm − 1 range are only related to the liberation of the MA cation³⁵.

Fig. 6.

The Raman spectra of thin-film halide perovskites with polymers were measured on FTO glass under an excitation wavelength of 532 nm.

The Raman spectroscopy analysis reveals that incorporating PVA, PVP, and PEG polymers into perovskite films significantly influences their structural integrity and stability by affecting the peak broadening, intensity, and shift. Among the tested concentrations (0.15 mg/ml, 0.3 mg/ml, and 0.6 mg/ml), the optimal concentration for all three polymers was 0.3 mg/ml. The films exhibited improved crystallinity, reduced structural defects, and enhanced stability at this concentration. PEG 0.3 mg/ml demonstrated the most favorable impact by reducing peak broadening, increasing peak intensity, and minimizing unwanted peak shifts, indicating enhanced structural uniformity and charge transport. Conversely, lower concentrations (0.15 mg/ml) provided insufficient surface coverage and limited defect passivation, while higher concentrations (0.6 mg/ml) induced mechanical stress, lattice distortion, and structural inhomogeneity, as evidenced by peak broadening and shifts to higher wavenumbers.

In conclusion, PEG at 0.3 mg/ml was identified as the most effective polymer additive for improving perovskite film properties, offering the best balance of stability, defect passivation, and electrical conductivity. Perovskite films at this concentration exhibit sharper Raman peaks and increased intensity, reflecting improved crystal quality and reduced lattice stress, factors vital for sustained device performance; their higher loadings resulted in polymer aggregation and phase separation, negatively impacting film integrity. Therefore, PEG 0.3 mg/ml is recommended as the optimal additive to achieve high-performance perovskite films with improved structural and optoelectronic characteristics.

The X-ray diffraction (XRD) analysis in (Fig. 7). confirms the successful formation of Cs₀.₁MA₀.₉PbI₃ perovskite films on the FTO substrate, with diffraction peaks observed at 14.16°, 20.03°, 28.42°, and 40.62°, corresponding to the (110), (112), (220), and (224) crystallographic planes. The distinct and intense peaks confirmed the perovskite material’s high crystallinity and tetragonal phase, vital for achieving optimal optoelectronic properties³⁶. These reflections confirm the successful formation of the perovskite structure. Moreover, the absence of a PbI₂-specific peak at around 12.6° indicates minimal phase decomposition.

It is important to note that the incorporated polymers (PEG, PVP, and PVA) are inherently amorphous or semi-crystalline. Their presence may reduce intensity and slightly broaden the perovskite diffraction peaks. This effect is primarily due to the increased amorphous background and peak overlap rather than degradation of the perovskite phase.

The presence of characteristic peaks for PEG20000 at 19.3° and 23.6° indicates partial incorporation of the polymer without disturbing the perovskite structure³⁷. However, with increasing PEG concentration, the peaks broaden, indicating increasing the structure’s amorphous content. According to Fig. 12, PEG 0.3 exhibits greater stability due to improved structure, morphology, and uniformity.

Fig. 12.

AFM topography of (a–c) pristine Cs0.1MA0.9PbI3 and (d–f) Cs_0.1MA_0.9PbI₃ modified by PEG 0.3 mg mL⁻¹ films on FTO glass: (a,d) 2D height, (b,e) 3D render, (c,f) line profiles.

Polyvinyl alcohol (PVA) films exhibit semi-crystalline characteristics, with peaks observed at 19.5° and in the range of 38.6°–40.47°, which are attributed to intra- and intermolecular hydrogen bonding^38,39. The addition of PVA improves the peak clarity and crystallinity. Increasing the peak intensity in about 14 (2teta) shows at all three PVA concentrations. However, increasing the concentration up to 0.6 mg/ml resulted in a broadening of the peak and a decrease in the intensity of the remaining peaks, indicating an increase in the semi-crystallite content in the structure.

Polyvinylpyrrolidone (PVP), which is known for its amorphous nature with distinct peaks at 11 and 21 degrees, was associated with a decrease in the sharpness of the perovskite peaks^40,41. A concentration of 0.3 mg/ml PVP provides an optimal balance between crystallinity and defect passivation, while higher concentrations (0.6 mg/ml) create excessive amorphous content, decreasing in peak intensity.

Consistent with previous reports, adding amorphous polymers can enhance crystallinity by moderating perovskite crystals’ nucleation and growth kinetics. Furthermore, the polymer chains can become incorporated within the film structure, slightly reducing the peak intensity and promoting a more uniform and stable crystalline morphology^42–44.

Additional high-intensity peaks observed in the polymer-containing films particularly near 26.5°, 33.8°, 37.9°, 51.7°,54.7°,61.9° and 65.9° originate from the FTO (fluorine-doped SnO₂) substrate (XRD patterns of FTO glass are provided in supplementary file Fig. S1)⁴⁵. The intensity of these reflections varies with perovskite layer thickness; thinner films permit greater X-ray penetration to the substrate, producing stronger FTO peaks, while thicker films attenuate them. Moreover, characteristic reflections of the polymers themselves (PEG20000 at ~ 19.3° and 23.6°, PVA at ~ 19.5° and 38.6–40.47°, and PVP broad features at ~ 11° and ~ 21°) are also visible, confirming partial structural retention of the additives after film fabrication.

Peak position analysis shows no significant shift (> 0.1°) in the main perovskite reflections after polymer incorporation. Minor variations can be attributed to lattice strain or interfacial interactions between polymer chains and perovskite grains.

Therefore, the slight reduction in peak intensity should not be interpreted as a sign of perovskite degradation but rather as an expected consequence of the structural influence of amorphous polymer additives. These findings align with prior studies, demonstrating that such additives can simultaneously modify XRD peak profiles and improve film quality and device performance.

The cyclic voltammetry (CV) analysis of Cs₀.₁MA₀.₉PbI₃ perovskite films with different polymer additives (PEG, PVA, and PVP) at varying concentrations (0.15 mg/ml, 0.3 mg/ml, 0.6 mg/ml) provides valuable perspectives on the electrochemical behavior of these materials. In the electrochemical analyses CV and EIS, A silver/silver chloride (Ag/AgCl) electrode served as the reference electrode, a Pt (platinum) electrode served as the counter electrode, and the perovskite-coated FTO functioned as the working electrode.

According to Fig. 8a, the results indicate that incorporating polymers can significantly influence the charge transport properties, defect passivation, and overall film stability. The CV curve show that the PEG 0.3 mg/ml sample demonstrates: a smooth and symmetric anodic and cathodic profile, indicating enhanced charge transfer kinetics and lower charge trapping.

Fig. 8.

CV curve of perovskite film with Polymers at 0.05 V. S-1 scan rate: (a) perovskite modified with PEG. (b) Perovskite modified with PVP. (c) Perovskite modified with PVA. (d) All samples of halide perovskites modified with polymers.

According to EIS analysis in (Fig. 9; Table 1), PEG 0.3 shows the lowest charge transfer resistance among the polymers, which confirms that PEG 0.3 conducts current better due to its symmetrical shape in Fig. 8⁴⁶. According to EIS analysis in (Fig. 9; Table 1), among the polymers, PEG 0.3 shows the lowest charge transfer resistance, which confirms that PEG 0.3 conducts current better due to its symmetrical shape in (Fig. 8). Moderate but stable current densities compared to PEG 0.15 and PEG 0.6. While PEG 0.15 exhibits a higher peak current, its curve’s sharp and asymmetric shape suggests possible instabilities due to excessive free carrier density and higher recombination.

Fig. 9.

Nyquist plots of the Perovskite film in 0.1 M LiClO4/C3H8O.

Table 1.

Electrochemical impedance parameters for halide perovskite modified by PVA, PVP, and PEG.

Sample	Rs (	CPE Y0 × 10−5(−1cm−2Snn		R_ct (cm2	Fitting error
Cs0.1MA0.9PbI3	646.97	0.21	0.62	1244	0.0021
Cs0.1MA0.9PbI3-PVP 0.15	493.99	0.99	0.82	1890	0.0023
Cs0.1MA0.9PbI3-PVP 0.3	457.1	1.33	0.78	1761	0.0035
Cs0.1MA0.9PbI3-PVP 0.6	505.49	1.25	0.80	2116	0.0024
Cs0.1MA0.9PbI3-PEG 0.15	506.38	1.85	0.73	2140	0.0015
Cs0.1MA0.9PbI3-PEG 0.3	510.29	1.45	0.76	1408	0.0024
Cs0.1MA0.9PbI3-PEG 0.6	520.35	1.44	0.78	1762	0.0015
Cs0.1MA0.9PbI3-PVA 0.15	547.28	2.98	0.67	1580	0.0038
Cs0.1MA0.9PbI3-PVA 0.3	501.80	1.47	0.73	2323	0.0012
Cs0.1MA0.9PbI3-PVA 0.6	500.04	2.21	0.67	2473	0.0029

PEG 0.6 shows lower current response and broader peaks, likely due to polymer overaccumulation, which leads to increased resistance, disruption of the crystal structure, and impaired charge mobility. PEG 0.3 appears to strike the optimal balance. Its CV profile is stable and reproducible, with a well-defined redox feature and efficient charge reversibility, suggesting a favorable interface for charge extraction.

PVA-modified films demonstrated moderate enhancement in charge transport, with the optimal concentration found at 0.3 mg/ml. This concentration effectively passivated defects while maintaining sound structural integrity⁴⁷. However, at higher concentrations (0.6 mg/ml), the broadening of the redox peaks was observed, indicating possible polymer-induced mechanical stress and reduced crystallinity, shown in (Fig. 8b). Additionally, at the same time PVA samples exhibit good peaks at positive voltage for PVA 0.3; their responses are often heterogeneous and display greater dispersion, which may affect overall performance. Similarly, in Fig. 8c, PVP 0.3 mg/ml showed improved electrochemical performance with sharper redox peaks, suggesting better defect passivation and charge transfer⁴⁸. However, at 0.6 mg/ml, PVP introduced amorphous regions, which negatively impacted charge transport and film stability. While PVP samples, particularly those at 0.3 and 0.6 mg/ml, demonstrate relatively good performance, their curves tend to be less symmetrical and smooth, which may influence their overall effectiveness.

In the analysis, we will have PL shown in Fig. 5 and CV shown in Fig. 8d analyses side by side: While it is true that the PL intensity of PEG 0.3 mg/ml is relatively lower than the control sample, it is important to emphasize that a lower PL intensity does not necessarily indicate increased defect density. In the context of perovskite films, reduced PL intensity can signify efficient charge extraction and radiative recombination quenching, suggesting improved carrier transport. Therefore, in this case, the quenching observed in PEG 0.3 may reflect enhanced charge separation and transfer, not necessarily higher recombination or more defects. In Fig. 8d, the findings suggest that PEG 0.3 mg/ml provides the best charge transport and defect passivation balance, making it the most suitable polymer for enhancing perovskite film performance. PVA and PVP also improve the film properties at 0.3 mg/ml, but higher concentrations may introduce unwanted effects such as structural disorder and reduced conductivity⁴⁹. Future work should focus on optimizing polymer-perovskite interactions to achieve further improvements in film stability and efficiency. Our study, based the conclusion on a synergistic interpretation of PL and CV results. The PEG 0.3 mg/ml sample showed a balance of lower recombination (via PL quenching) and enhanced charge mobility (via higher CV current), making it a promising candidate for improved overall performance.

In this study, the impact of PVP, PVA, and PEG polymers at concentrations of 0.15, 0.3, and 0.6 mg/ml on the impedance behavior of Cs₀.₁MA₀.₉PbI₃ perovskite films was investigated in 0.1 M LiClO₄/C₃H₈O electrolyte. EIS measurements were performed at open circuit potential (OCP) within the 100 kHz to 10 mHz frequency range.

The Nyquist plot in (Fig. 9) reveals that polymer additives significantly influence charge transfer resistance (Rct) and charge carrier mobility. Rs denotes the solution resistance, Rct signifies the charge transfer resistance, and CPE stands for the constant phase element shown in the equivalent circuit, (Fig. 9).

According to (Fig. 9), the 0.3 mg/ml concentration exhibited the best performance in PVA-modified films, reducing charge transfer resistance and improving interfacial contact due to hydrogen bonding interactions between PVA functional groups and the perovskite lattice. Conversely, increasing the concentration to 0.6 mg/ml resulted in adverse effects. Specifically, this led to a higher charge transfer resistance (R_ct) and decreased electrical conductivity, probably due to polymer agglomeration and diminished film crystallinity⁵⁰. PVP-modified perovskite films exhibited a similar trend, significantly reducing charge transfer resistance at 0.3 mg/ml. This reduction indicates an increase in both ionic conductivity and electrochemical stability. However, at 0.6 mg/ml, R_ct increased due to the formation of amorphous regions, which hindered charge transport pathways and promoted electron-hole recombination⁵¹. Compared to the other polymers, PEG-modified films significantly reduced charge transfer resistance, particularly at 0.3 mg/ml, which exhibited the lowest R_ct among all samples. The beneficial effect is probably linked to the robust interaction of PEG with the perovskite lattice, boosting charge carrier mobility. However, exceeding this concentration to 0.6 mg/ml resulted in a higher charge transfer resistance, likely stemming from phase segregation and structural imperfections⁵².

According to Table 1, The results indicate that polymer modification significantly influences charge transfer resistance in halide perovskite films. Rs denotes the solution resistance, Rct signifies the charge transfer resistance, and CPE stands for the constant phase element Characterized by Y₀ and the exponent n; it describes the film’s capacitive behavior and surface roughness. Among all tested samples, PEG 0.3 mg/ml exhibited the lowest Rct (1408 Ω·cm²) compared to the control sample, suggesting that it best balances defect passivation and charge transport enhancement. The PEG 0.3 mg/ml modified film shows a moderate Rct (1408 Ω·cm²), yet it demonstrates a significantly higher CPE (1.45 × 10⁻⁵ Ω⁻¹·cm⁻²·sⁿ) and improved n (0.76), suggesting more favorable interfacial capacitive behavior. Additionally, cyclic voltammetry measurements confirm improved charge transport for PEG 0.3 mg/ml, as evidenced by its more symmetric and higher current response. While PVP 0.3 mg/ml also demonstrated good performance (1761 Ω·cm²), higher concentrations increased resistance. PVA-modified films exhibited the highest charge transfer resistance, particularly at 0.3 and 0.6 mg/ml, suggesting that excessive PVA hinders charge transport. Based on these findings, PEG at 0.3 mg/ml is the most effective polymer additive for optimizing charge transfer in perovskite films.

EIS analysis indicates that, for all investigated polymers, the 0.3 mg/ml concentration provides optimal performance, leading to reduced charge transfer resistance and enhanced charge carrier mobility. In contrast, the 0.6 mg/ml concentration resulted in performance degradation due to increased recombination and structural defects. Among the studied polymers, PEG at 0.3 mg/ml demonstrated the best performance, making it the most promising candidate for improving the electrochemical properties of perovskite films, consistent with the CV result.

Although the charge transfer resistance increased with the addition of polymers compared to the control sample, Fig. 12 clearly shows that PEG at a concentration of 0.3 mg/mL ultimately enhances the stability of all samples by passivating defects and increasing crystal size.

FESEM images were taken from the samples that exhibited the best optical and structural properties (PVP 0.3 mg/ml, PEG 0.3 mg/ml, PVA 0.3 mg/ml).

Figure 10 shows that all perovskite films display a needle-like crystalline structure. The SEM analysis of the perovskite films modified with PVP, PEG, and PVA reveals significant morphological changes compared to the pristine Cs₀.₁MA₀.₉PbI₃ sample. As shown in Fig. 10a, the pristine perovskite film exhibits relatively tiny and dispersed crystal structures at two µm magnification. However, the crystal sizes have noticeably increased after polymer modification, as observed in Fig. 10b–d, which were captured at 10 μm magnification. Although the PVA 0.3 sample demonstrates the most substantial increase in crystal size, indicating its strong impact on the growth and structuring of perovskite grains, notable surface cracks, and intergranular defects are still present. These morphological imperfections likely arise from several interrelated factors. First, the increased viscosity of the precursor solution due to PVA slows solvent evaporation, leading to non-uniform drying and localized stress accumulation during crystallization. Second, the thermal expansion mismatch between the perovskite matrix and the PVA polymer introduces additional mechanical stress during annealing and subsequent cooling. Furthermore, although grain growth is enhanced, poor grain-to-grain connectivity potentially caused by the influence of PVA on nucleation and crystal growth may result in mechanically weak boundaries. Combining these effects contribute to the concentration of internal stresses and ultimately promotes crack formation across the film surface.

Increasing crystal size is generally associated with enhanced film quality and stability. Larger crystals contain fewer grain boundaries, reducing the pathways for moisture and oxygen infiltration, which are the primary causes of perovskite degradation. This finding is based on the established literature, where researchers have reported that improving crystal size reduces defect density, enhances charge transport, and increases the operational lifespan of perovskite-based devices⁵³. Additionally, larger grain structures have been found to minimize ion migration and slow down the degradation process, as demonstrated in research by Zhou et al.⁵⁴.

The observed morphology is consistent with lead-based perovskite films prepared at a 1:1 MAI: PbI₂ molar ratio, and is further modified by the presence of polymer additives. Unlike hot-gun induced needle-like structures reported elsewhere, our films were fabricated under controlled humidity (< 30% RH) without hot-air assistance, producing relatively uniform coverage.

The cross-sectional SEM image (Fig. 10e) confirms that the perovskite layer in the PEG 0.3 mg/mL sample has an average thickness of approximately 500 nm, with only minor local variations. This thickness is optimal for balancing light absorption and carrier transport, contributing to both efficiency and stability. The crystalline nature of the films is further supported by XRD analysis (Fig. 7).

Ultimately, incorporating PVP0.3 and PEG0.3, along with PVA 0.3, which shows particular promise, enhances the crystalline characteristics of the perovskite film by increasing crystal domain size and structural robustness. These improvements are expected to lead to a longer device lifespan by mitigating the negative impact of environmental factors.

Figure 11 illustrates the EDS spectrum and corresponding elemental mapping of the Cs₀.₁MA₀.₉PbI₃ film modified with 0.3 mg/mL PEG (a-1 to a-4). The inset table (a-2) provides the estimated Weight and area percentages of Cs, MA, Pb, I, C, N, and O, as determined by semiquantitative EDS analysis. These values were obtained through software processing of an averaged signal collected from thousands of scanned particles, ensuring reliable compositional representation. The mapping confirms a homogeneous spatial distribution of all key elements (Cs, Pb, I, C, N, O) related to Cs_0.1MA(CH₃NH₃)_0.9PbI₃-PEG(HO(C₂H₄O)_nH)0.3 mg/ml across the film surface, consistent with the SEM microstructure.

Fig. 11.

Elemental analysis and mapping using EDS spectroscopy were performed on Cs0.1MA0.9PbI3 that was modified with PEG at a concentration of 0.3 mg/ml.

To further evaluates surface uniformity, atomic force microscopy (AFM) analysis was conducted, as shown in (Fig. 12). The pristine perovskite film (Fig. 12a–c) exhibits a rough surface with Ra ≈ 35.30 nm and Rq ≈ 42.03 nm. After incorporating PEG at 0.3 mg mL⁻¹ (Fig. 12d–f), roughness significantly decreases to Ra ≈ 22.19 nm and Rq ≈ 28.86 nm, indicating a smoother and more homogeneous surface in scanned area 8 × 8 μm².

This improvement is attributed to the chemical passivation effect of PEG. The hydroxyl (–OH) and ether oxygen groups along PEG chains can coordinate with under-coordinated Pb²⁺ ions and passivate iodide vacancies, thereby reducing trap states at grain boundaries. These passivation effects mitigate non-radiative recombination and improve grain connectivity, resulting in denser and more uniform film coverage.

This role of PEG in improving morphology and passivating perovskite films aligns with prior findings. For example, Yibo You et al. reported that PEG used as a perovskite precursor additive significantly improved film quality, producing smoother surfaces with noticeably reduced roughness and minimized pinhole formation⁵⁵.

The AFM results confirm that polymer-modified films—particularly those with PEG 0.3 mg mL⁻¹ exhibit reduced roughness and improved morphological uniformity. These structural improvements directly underpin the enhancements observed in the films’ optical and electrical performance.

The images in Fig. 13 illustrate the long-term stability of polymer-modified halide perovskite films under ambient conditions (30% relative humidity, room temperature) over 1000 h. Degradation is visually apparent as perovskite films change color. Initially dark grayish-black (Fig. 13a), most samples develop a yellow tint over time, indicating environmental breakdown (Fig. 13b–d).

Fig. 13.

Evaluation of long-term stability in halide perovskite layer modified with polymers (PVP, PVA, PEG) at room temperature with a relative humidity of 30%: (a) Immediately after layer deposition and annealing (b) after 350 h from layer deposition. (c) after 700 h from layer deposition. (d) after 1000 h from layer deposition.

Color retention demonstrates the stabilizing effect of polymers. The PEG 0.3 mg/ml film shows the best stability, maintaining its initial color after 1000 h (Fig. 13d). This suggests that PEG plays a crucial role in inhibiting the degradation mechanisms that typically affect perovskites, such as moisture-induced decomposition and ion migration^56,57. The enhanced stability arises from PEG’s ability to passivate defects, reduce ion mobility, and create a protective barrier against environmental factors.

Compared to PEG, perovskite films with PVP and PVA showed varying degradation levels, with higher polymer concentrations (0.6 mg/ml) leading to increased yellowing, indicating instability. The rapid degradation of the control sample (unmodified perovskite film Cs_0.1MA_0.9PbI₃) highlights PEG’s effectiveness as a stabilizer.

These results demonstrate that polymer engineering can enhance perovskite stability. Specifically, PEG at an optimal concentration (0.3 mg/ml) significantly improves the resilience of perovskite layers against environmental factors, making it a strong candidate for robust perovskite-based optoelectronic technologies.

Conclusion

In this study, we systematically assessed the impact of incorporating PEG at different concentrations on the structural and functional properties of Cs₀.₁MA₀.₉PbI₃ perovskite films. Among the concentrations tested, 0.3 mg/ml PEG struck the best balance, enhancing film uniformity, reducing charge transfer resistance, and improving optoelectronic characteristics. These enhancements were achieved without compromising the films’ crystallographic integrity or homogeneity. Our findings highlight the significance of optimizing polymer additive content to effectively boost the stability and efficiency of perovskite solar cells under ambient conditions. This work represents a meaningful step toward developing more stable and scalable fabrication approaches for high-efficiency perovskite photovoltaics.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

M.B. Conceptualization, Methodology, Writing—original draft preparation. A.N. Conceptualization, writing—reviewing and editing, Supervision. E.A. Conceptualization, writing—reviewing and editing. S. J. P. Conceptualization, Writing—reviewing and editing.N.D. Conceptualization, Writing—reviewing and editing.

Data availability

All data generated or analysed during this study are included in this published article.

Declarations

Competing interests

The authors declare no competing interests.