Okba Saidania,
Souraya Goumri-Said*b,
Abderrahim Yousfia,
Girija Shankar Sahooc and
Mohammed Benali Kanoun
d
aETA Laboratory, Department of Electronics, Faculty of Sciences and Technology, University Mohamed El Bachir El Ibrahimi of Bordj Bou Arréridj, 34030, Algeria. E-mail: okba.saidani@univ-bba.dz
bCollege of Science and General Studies, Physics Department, Alfaisal University, P.O. Box 50927, Riyadh 11533, Saudi Arabia. E-mail: sosaid@alfaisal.edu
cSchool of Electronics Engineering (SENSE), Vellore Institute of Technology, Vandalur-Kellambakkam Road, Chennai, Tamil Nadu 600127, India
dDepartment of Mathematics and Sciences, College of Humanities and Sciences, Prince Sultan University, P.O. Box 66833, Riyadh 11586, Saudi Arabia. E-mail: mkanoun@psu.edu.sa
First published on 7th March 2025
This study presents a high-efficiency perovskite solar cell structure, incorporating a Cs0.05(FA0.77MA0.23)0.95Pb(I0.77Br0.23)3 as absorber, PCBM as the electron transport layer (ETL), and CuSbS2 as the hole transport layer (HTL). First-principles calculations were conducted to explore the electronic and optical properties of these materials, revealing a high absorption coefficient of approximately 105 cm−1, making the perovskite an excellent absorber. The SCAPS-1D simulation tool was employed to evaluate the photovoltaic performance of the ITO/PCBM/mixed perovskite/CuSbS2/Ag device. Various factors such as different HTLs and ETLs, absorber thickness, ETL and HTL thickness, defect concentration, temperature, and resistance were analyzed to optimize device performance. The results demonstrate that the optimized configuration achieves an outstanding power conversion efficiency of 28.01%, with an open-circuit voltage of 1.12 V, a short-circuit current density of 29.84 mA cm−2, and a fill factor of 83.78%. Notably, the study found that HTL thickness variations have a more dominant impact on efficiency than perovskite thickness, emphasizing the importance of transport layer engineering. The findings offer a promising pathway for further research on material optimization, stability enhancement, and large-scale fabrication, paving the way for the next generation of perovskite solar technologies.
Compositional engineering has emerged as a key strategy for enhancing the performance and stability of perovskite solar cells. Among various perovskite materials, cesium (Cs)-based perovskites exhibit superior thermal stability, making them highly suitable for long-term applications.18 Cs+ incorporation stabilizes the α-phase by optimizing the Goldschmidt tolerance factor, thereby improving structural integrity and phase stability.18 Beyond Cs+ doping, mixed-cation perovskites have gained significant attention due to concerns over lead toxicity and the need for enhanced optoelectronic properties.19 The partial substitution of Cs, methylammonium (MA), and formamidinium (FA) in perovskite compositions such as (Cs/MA/FA)Pb(I/Br)3 offers notable advantages, including improved mechanical robustness, enhanced thermal stability, and intrinsic moisture resistance. These properties, combined with their tunable bandgaps, make mixed-cation perovskites particularly promising for flexible and tandem perovskite solar cells.20 The bandgap engineering plays a crucial role in optimizing energy absorption and charge transport. Advanced mixed-cation, mixed-halide perovskites with carefully tuned bandgaps and optimized p–i–n device architectures have led to significant efficiency gains. Notably, triple-cation compositions (FA, MA, Cs) with bandgaps ranging from 1.59 to 1.68 eV have achieved higher efficiencies as an absorber layer in PSCs, demonstrating their potential for high-performance photovoltaic applications.21–23 Regardless of the bandgap of perovskite material and its energy level alignment with adjacent charge transport layers, selecting optimal electron transport layer (ETL) and hole transport layer (HTL) materials is crucial for designing high-performance single-junction perovskite solar cells. The ETL plays a vital role in PSCs, facilitating efficient charge extraction and transport. Among the most promising ETL materials, tin oxide (SnO2)24 and phenyl-C71-butyric acid methyl ester (PCBM)25,26 offer several advantages, including high electron mobility, a wide bandgap, chemical stability, and excellent optical transmittance. Additionally, their low-temperature processability makes them suitable for flexible and lightweight substrates, expanding the potential for next-generation photovoltaic applications. Similarly, the HTL is essential for optimizing PCE by ensuring efficient hole extraction and reducing recombination losses. Copper thiocyanate (CuSCN)27 and (CuO2)28 have emerged as promising HTL candidates due to their high hole mobility, favorable energy level alignment with perovskite materials, and ability to suppress recombination at the HTL/perovskite interface. Among emerging HTLs, (copper antimony sulfide) (CuSbS2) offers distinct advantages, including well-matched energy levels with the absorber layer, which enhances hole collection and transport while minimizing energy losses. Moreover, its excellent chemical stability and compatibility with perovskite materials contribute to improved device longevity. The high absorption coefficient and superior optical properties of CuSbS2 further boost light absorption, leading to enhanced photoconversion efficiency.29,30 The performance of mixed-cation lead halide perovskite solar cells has been extensively studied through experimental research21,22,31–33 to achieve higher efficiencies. However, to the best of our knowledge, theoretical investigation23 on device performance and performance modeling for mixed perovskite solar cells remain limited.
In this study, we investigate a Cs0.05(FA0.77MA0.23)0.95Pb(I0.77Br0.23)3-based perovskite solar cell, exploring various hole transport layers (HTLs)—V2O5 (vanadium pentoxide), CuO2, CuSCN, CBTS (copper bismuth thiophosphate), and CuSbS2—and electron transport layers (ETLs)—SnO2, ZnO, C60, IGZO (indium gallium zinc oxide), and PCBM. Using SCAPS-1D simulations, we systematically evaluate these ETL-HTL combinations to identify the optimal theoretical pairing within an ITO/ETL/perovskite/HTL/Ag architecture. To further validate the structural and optical properties of the selected perovskite absorber, we perform first-principles calculations based on density functional theory (DFT), confirming its band gap characteristics. Additionally, we analyze the impact of absorber and ETL thicknesses on photovoltaic performance, as well as the effects of series (Rs) and shunt (Rsh) resistance and operating temperature on the best-performing configuration. By unraveling the intricate interplay of these parameters, our study provides valuable insights into efficiency and stability optimization in perovskite solar cells. This comprehensive theoretical investigation not only enhances the fundamental understanding of device physics but also paves the way for future advancements in perovskite-based photovoltaics.
The proposed device architecture for simulating a high-efficiency PSC, as shown in Fig. S1,† comprises of multiple layers with specific thicknesses and material compositions: ITO (0.05 μm), PCBM (0.1 μm), mixed perovskite (0.4 μm), and CuSbS2 (0.1 μm). ITO (indium tin oxide) is a transparent conducting oxide exploited like bottom contact, allowing light to pass through while providing a conductive surface for electron flow. PCBM (phenyl-C61-butyric acid methyl ester), a fullerene derivative commonly used as an electron acceptor in organic solar cells, acts as the efficient ETL by extracting electrons generated by the material that absorbs radiance.37 The mixed perovskite is the key of PSC, the suggested absorber, is a mixed-halide perovskite material composed of Cs, FA, MA, Pb, iodine(I), and bromine (Br). This layer absorbs sunlight and generates electron–hole pairs, initiating the photovoltaic effect. CuSbS2 serves as HTL, promoting the movement of holes, or positive charges, from the mixed perovskite layer to the front contact, making it a promising material for enhancing the cell's overall efficiency.38 Besides, Tables S1 and S2† provide the input parameters of the absorption coefficient values used for each layer as well as the electrical properties of the interfaces. The simulations were carried out under standard conditions, specifically at 300 K ambient temperature and AM 1.5 G lighting. Additionally, we took great care in defining the simulation parameters for the different HTLs, ETLs, and the absorber, as elaborated in Tables S3 and S4.†
The SCAPS-1D39 software effectively solves the equations governing Poisson, continuity, and drift-diffusion. The following eqn (1) is a basic building block for comprehending charge distribution and electrostatics in semiconductor materials. The electric field E can be expressed as the gradient of the electrostatic potential ϕ.40
![]() | (1) |
![]() | (2) |
![]() | (3) |
![]() | (4) |
![]() | (5) |
The charge is represented by q, the carrier mobilities by μp, μn, and the diffusion coefficients by Dp, Dn.
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Fig. 1 Computed band structures of (a) mixed-cation lead halide perovskite and (b) CuSbS2. (c) Illustration of the HOMO and LUMO of PCBM molecule. |
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Fig. 2 Partial density of the states of (a) mixed-cation lead halide perovskite and (b) CuSbS2 in the equilibrium geometry. The Fermi level was positioned along the dashed black line. |
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Fig. 3 Calculated optical absorption coefficients for mixed-cation lead halide perovskite (top) and CuSbS2 (bottom). |
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Fig. 4 (a) Effect of different ETL layers (b) effect of different HTL layers of the performance of PSC. |
The impact of the mixed perovskite layer thickness on the J–V characteristics of the proposed PSC structure is depicted in Fig. 5(a). As the thickness increases from 0.2 μm to 1.4 μm, the JSC exhibits a notable rise. This trend can be attributed to enhanced light absorption with increasing absorber thickness, which leads to greater photogenerated charge carriers. However, beyond a certain thickness, recombination losses may counteract this benefit, causing JSC to saturate or slightly decline.28 Fig. 5(b) further analyzes the effect of thickness variation on the photovoltaic parameters, including VOC, JSC, FF, and PCE. The VOC follows a decreasing trend as the absorber thickness increases. This decline is primarily caused by increased charge carrier recombination within thicker layers, which hinders charge extraction efficiency. The FF initially increases from 82.5% to 84.4% with thickness but stabilizes beyond 1.0 μm. This behavior suggests that an optimal thickness range exists where series resistance is minimized, ensuring efficient charge transport. The PCE reaches its peak at an absorber thickness of 0.8 μm, achieving a maximum value of 22.5%. Beyond this point, further increasing the thickness results in a slight decline in efficiency, likely due to diminishing gains in JSC and increased recombination losses.51 These findings highlight the importance of optimizing the absorber layer thickness to balance light absorption, charge transport, and recombination effects. The simulation results indicate that an optimal mixed perovskite layer thickness of 0.8 μm provides the highest efficiency for the proposed PSC device. This optimization is critical for enhancing overall device performance and achieving high-efficiency, stable perovskite solar cells.
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Fig. 5 (a) J–V characteristics; (b) effect of thickness of absorber layer in VOC, JSC, FF and PCE. (c) J–V characteristics; (d) effect of thickness of CuSbS2 HTL in VOC, JSC, FF and PCE. |
The effect of CuSbS2 HTL thickness on the photovoltaic performance of the perovskite solar cell is analyzed in Fig. 5(c) and (d). As shown in Fig. 5(c), the J–V characteristics indicate that increasing the HTL thickness from 0.1 μm to 0.5 μm results in a decrease in JSC. This decline is primarily due to increased charge transport resistance within the thicker HTL, which limits the efficient extraction of photogenerated carriers. Fig. 5(d) further illustrates the variations in the key PV parameters as a function of CuSbS2 thickness. The JSC decreases from 22 mA cm−2 to 14 mA cm−2 with increasing HTL thickness, which can be attributed to reduced light absorption and enhanced recombination losses in thicker layers. The VOC remains relatively stable, suggesting that changes in HTL thickness do not significantly alter the energy band positions or the alignment of Fermi levels at the interfaces. However, both FF and PCE exhibit a declining trend as the HTL thickness increases beyond 0.1 μm. The increase in series resistance associated with a thicker HTL contributes to this deterioration in performance. These findings emphasize the necessity of optimizing the CuSbS2 HTL thickness to balance hole extraction efficiency, minimize recombination losses, and maintain low contact resistance.52 The optimal thickness of 0.1 μm ensures efficient charge transport while avoiding excessive resistive losses, thereby maximizing the overall performance of the PSC. Optimizing the ETL thickness in a PSC is crucial for achieving efficient electron extraction, minimizing contact and series resistance, reducing charge recombination, and ensuring proper energy level alignment. If the ETL is too thick, charge carriers experience longer transit times, increasing the likelihood of recombination at defect sites. Additionally, ETL thickness impacts energy level alignment at the absorber interface, where an optimal thickness facilitates efficient charge transfer while minimizing energy losses.53 To identify the optimal ETL thickness, we varied it from 0.1 μm to 0.5 μm in increments of 0.1 μm. As shown in Fig. S4,† a thickness of 0.1 μm delivers the best device performance.
Fig. 6(a) and (b) illustrate the significant impact of defect density on the electrical characteristics and overall performance of PSCs. In Fig. 6(a), the J–V curves shift considerably as the defect density increases from 1010 cm−3 to 1018 cm−3, highlighting the role of trap-assisted recombination. At low defect densities (≤1015 cm−3), the device maintains a high JSC of approximately 24.2 mA cm−2, indicating minimal recombination losses and efficient charge transport. However, as the defect density increases beyond 1016 cm−3, JSC decreases drastically, reaching ∼14 mA cm−2 at 1018 cm−3, due to enhanced recombination and reduced carrier lifetime. Fig. 6(b) further confirms these trends by illustrating the relationship between defect density and key photovoltaic parameters. The results indicate that VOC remains relatively stable at 0.98 V for defect densities up to 1015 cm−3, but decreases to 0.94 V at 1018 cm−3. Similarly, the FF, which remains around 86% for defect densities below 1015 cm−3, drops significantly to ∼70% at 1018 cm−3, reflecting increased charge carrier scattering and higher series resistance. The PCE follows the same trend, starting at ∼20% for defect densities ≤1014 cm−3, but dropping sharply to <10% for densities exceeding 1017 cm−3. This highlights how excessive defect concentrations lead to increased non-radiative recombination, reducing overall device efficiency. To mitigate these negative effects, minimizing defect concentrations in the perovskite absorber layer is crucial. Strategies such as optimizing fabrication processes, improving material purity, introducing defect passivation layers, and developing defect-tolerant perovskite compositions are essential for achieving high-performance and stable PSCs. Understanding and controlling defect-related losses remain key factors in advancing next-generation photovoltaic technologies.
Fig. 7(a) and (b) illustrate the J–V characteristics and impact of temperature variations on the performance of PSCs, with a focus on key photovoltaic parameters. The results confirm that increasing temperature from 240 K to 360 K negatively affects overall device performance, primarily due to enhanced non-radiative recombination and changes in resistive losses. As observed in Fig. 7(b), the VOC exhibits a consistent decline with increasing temperature. This effect arises due to higher carrier recombination rates at elevated temperatures, which reduce the quasi-Fermi level splitting. VOC drops from approximately 1.052 V at 240 K to 0.85 V at 360 K, indicating a thermal-driven energy loss mechanism. Consequently, the PCE follows the same trend, decreasing from around ∼23.8% at 240 K to 18% at 360 K, confirming the strong correlation between temperature and recombination losses. In contrast to VOC, the JSC remains relatively stable across the temperature range. The stability of JSC in PSCs indicates that temperature-induced losses are mainly due to increased recombination rather than changes in charge generation.52 The FF is significantly impacted by temperature, decreasing from ∼87% at 240 K to ∼79% at 360 K. This decline is attributed to increased Rs and reduced Rsh at higher temperatures, leading to efficiency losses. The increase in Rs impedes charge transport, while lower Rsh facilitates leakage currents, further degrading FF and the overall performance. These results highlight the necessity of thermal stability optimization in PSCs.
Fig. 8(a) and (b) illustrate the variations in photovoltaic parameters of PSCs with changing series resistance (Rs) and shunt resistance (Rsh). The optimization of these resistances plays a critical role in maximizing PSC performance and stability. As observed in Fig. 8(a), increasing Rs from 2 Ω cm2 to 10 Ω cm2 results in a significant decline in FF and PCE. When Rs = 2 Ω cm2, the device achieves a high FF of approximately 80% and PCE close to 18%. However, at Rs = 10 Ω cm2, both FF and PCE drop significantly, with FF reducing to ∼40% and PCE falling below 10%. This confirms that excessive Rs induces voltage losses, increasing power dissipation and reducing device efficiency. Notably, JSC remains relatively stable across the range of Rs, staying between 20–24 mA cm−2, indicating that series resistance primarily affects voltage-dependent parameters rather than current generation. Fig. 8(b) shows the impact of varying Rsh from 104 Ω cm2 to 108 Ω cm2. Higher Rsh values lead to improved device performance by suppressing leakage currents. At Rsh = 108 Ω cm2, the device exhibits a VOC close to 1.05 V, FF around 85%, and a PCE exceeding 20%. In contrast, when Rsh = 104 Ω cm2, the FF drops to 50%, and the PCE falls below 12%, indicating significant recombination losses due to shunt pathways. Notably, JSC remains relatively unaffected, hovering between 22–24 mA cm−2, reinforcing the notion that Rsh mainly influences voltage-related losses rather than photocurrent generation. Achieving high-performance PSCs requires minimizing series resistance (Rs < 2 Ω cm2) and optimizing shunt resistance (RSh > 107 Ω cm2). The findings imply that resistive losses mostly impact voltage-dependent parameters like VOC, FF, and PCE because JSC is rather stable despite changes in Rs and Rsh. While a high Rsh decreases recombination losses, improving VOC and overall efficiency, a high Rs increases series resistance losses, decreasing FF and PCE.54 The maximum PCE (∼20%) is obtained under the optimum conditions (Rs = 2 Ω cm2, Rsh ≈ 108 Ω cm2), indicating that careful resistance engineering is essential for PSC performance. In order to create robust and effective perovskite-based photovoltaics, these results highlight the necessity of improving Rs and Rsh through material selection, fabrication methods, and device engineering.
For the final optimization of the simulated device, a mixed perovskite layer with a thickness of 0.8 μm and a defect density of 1017 cm−3 was selected. Fig. 9 and 10 illustrate the influence of ETL and HTL thickness on the performance of the FTO/PCBM/mixed perovskite/CuSbS2 device. The results indicate that a 1.8 μm-thick mixed perovskite layer effectively captures AM 1.5 insolation, minimizing reliance on light reflected from the back electrode. This suggests that the proposed design optimizes light absorption and charge transport without requiring additional optical enhancements. Fig. 10 demonstrates the influence of ETL (0.1–0.5 μm) and absorber thickness (0.2–1.4 μm) on the photovoltaic performance of PSCs, revealing complex trade-offs between light absorption, charge transport, and recombination. The VOC reaches a peak of 0.96 V at an absorber thickness of 0.2 μm with an ETL of 0.1–0.3 μm, but declines with increasing absorber thickness due to enhanced reverse saturation current. The JSC improves with absorber thickness up to an optimal range, beyond which bulk recombination limits further gains. The FF remains high when both layers are optimized, as excessive thickness introduces series resistance and charge recombination losses. Consequently, the highest PCE is observed for absorber thicknesses of 0.6–1.0 μm and ETL thicknesses of 0.1–0.3 μm, balancing light absorption and charge extraction. The results from Fig. 9 emphasize the importance of carefully tuning the ETL and absorber thickness to achieve an optimal balance between light absorption, charge generation, and transport. While a thicker absorber increases JSC, it can also lead to higher recombination losses, negatively affecting VOC and FF. Similarly, an optimal ETL thickness is required to facilitate efficient electron extraction without introducing excessive series resistance. These findings highlight the necessity of jointly optimizing these layers to minimize recombination and resistance losses, thereby maximizing device efficiency and stability.
The 3D plots illustrate the effects of changing the HTL and mixed perovskite thicknesses on solar cell performance (Fig. 10). The mixed perovskite layer thickness varies between 0.2 and 1.4 μm, while the HTL thickness ranges from 0.1 to 0.5 μm. The JSC increases notably with mixed perovskite thickness, reaching approximately 30 mA cm−2 at 1.4 μm, demonstrating enhanced light absorption. However, the VOC declines from 0.97 V to ∼0.89 V beyond 1.0 μm, indicating higher recombination losses. The FF initially increases but stabilizes at ∼84.4% when the mixed perovskite thickness exceeds 1.0 μm, showing that further increases have minimal impact. The PCE peaks at ∼22.5% with an optimal 0.8 μm mixed perovskite and 0.1 μm HTL thickness, achieving a balance between light absorption, charge transport, and recombination losses.55 These trends suggest that while a thicker mixed perovskite layer enhances absorption, excessive thickness leads to VOC degradation and charge transport limitations. The dominance of HTL thickness variations over mixed perovskite in optimizing PCE underscores the importance of finely tuning both layers to minimize series resistance and recombination while maximizing carrier extraction efficiency.
Table 1 compares our results with existing theoretical and experimental studies on mixed perovskite-based PSCs. Our optimized configuration achieved a maximum PCE of 28.01%, significantly outperforming previous experimental and simulation studies,23 which reported efficiencies of around 20%. To refine device performance, we conducted a comprehensive simulation to identify the most efficient ETL, HTL, and their key properties. The primary objective of these simulations was to determine the optimal material combinations that yield the highest efficiency. Notably, our studied configurations demonstrated superior performance compared to previous simulations, offering valuable insights for future device optimization. This substantial improvement underscores the superiority and potential of optimized solar cell designs, paving the way for further advancements and innovations in photovoltaic technology.
Footnote |
† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra08323g |
This journal is © The Royal Society of Chemistry 2025 |