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Scientific Reports volume 15, Article number: 13170 (2025) Cite this article
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This study focuses on optimizing the efficiency of lead-free perovskite solar cells (PSCs) using CH₃NH₃SnI₃ as the active layer. Various modifications were investigated to enhance the performance of the PSCs. Key adjustments included the choice of polymer as a hole-transporting material (HTM), electrode materials, device structure, and the incorporation of a thin layer of nickel oxide (NiO) as a hole-selective layer (HSL). The results demonstrate that replacing ZnTe with TAPC polymer as the HTM led to a significant increase in power conversion efficiency (PCE) due to better band alignment and electron-blocking properties. Additionally, substituting the expensive gold electrode with aluminum was facilitated by incorporating a PEDOT conductive polymer buffer layer to improve carrier extraction efficiency. Transitioning from a traditional n-i-p structure to a p-i-n inverted structure and optimizing TiO₂ placement further enhanced light absorption and device current. The introduction of a thin NiO layer, optimized at 5 nm thickness, contributed to improved PCE, short-circuit current density (J_sc), and open-circuit voltage (V_oc). Ultimately, the optimized PSC structure yielded an impressive PCE of 12.37%, indicating a substantial advancement in efficiency compared to previous studies. These findings underscore the potential of lead-free perovskite materials, particularly CH₃NH₃SnI₃, in revolutionizing solar energy technology toward a more sustainable and efficient future.
Sustainable energy sources for day-to-day consumption have received significant attention in recent decades. In the last decade, scientists have done a lot of research to find solar cells with potential replacements for conventional silicon-based solar cells. Much of the research was conducted in perovskite solar cells (PSCs) and showed exponential linear regression in efficiency. Consequently, PSCs become one of the most promising photovoltaic technologies. In this context, perovskites, such as MAPbI₃, FAPbI₃, and mixed-cation perovskite materials, have been applied to fabricate high-performance solar cells¹. However, these types of perovskite structures are toxic and based on Pb, consequently limiting the applicability of these types of cells. Therefore, it is important to find a new structure of perovskite without Pb to construct PSCs that are environmentally friendly^{2,3,4,5,6,7,8}.
Among these substitutes, halide perovskites based on tin (Sn) (ASnX₃) have shown advantageous properties, which include a high absorption coefficient and a narrow band gap (around 1.3 eV)^{9,10,11,12,13}. With improved stability, a wider visible spectrum coverage, and a reduced recombination rate, this lead-free perovskite version offers an appealing alternative to the drawbacks of conventional lead-containing materials. In comparison to their lead-based equivalents, Sn perovskite solar cells have a shorter diffusion length that enables electron production closer to the electron collector layer, greatly enhancing electron collecting and lowering recombination rates^{2,3,4,5,6,7,8,14,15,16,17}. Accordingly, perovskites based on Sn could produce solar cells with a higher short-circuit current density (J_sc), close to the theoretical efficiency limit. Therefore, Sn-based perovskites such as CH₃NH₃SnI₃ are very promising for the fabrication of high-performance lead-free eco-friendly PSCs^18,19,20.
Temperature is another crucial parameter that significantly affects the performance and stability of perovskite materials based on lead halides. These materials can show phase changes and fast degradation at high temperatures. For example, methylammonium lead halide perovskites rapidly degrade PSC’s performance at temperatures above 150 °C by breaking down into lead iodide (PbI₂)²¹. However, non-toxic alternatives perovskite based on tin can be a better choice regarding thermal stability. Recent investigations have revealed that tin (Sn)-based perovskites (MASnI₃, FASnI₃) have rather high thermal stability and sustain structural integrity up to 200 °C. Strong bonding within the Sn–I framework accounts for this increased stability^22,23. Along with the excellent thermal stability, these materials exhibit a charge carrier density of ~ 8 × 10¹⁷ cm⁻³ and a charge carrier mobility of ~ 22 cm²/Vs^22,24,25. These optoelectronic properties make them an excellent choice for solar cell applications.
Inverted planar PSCs with p–i–n arrangement based on Sn perovskites have attracted many researchers because of their simple fabrication and low cost^26,27. Whereas the performance of these PSCs is still much lower than that based on Pb perovskites. Consequently, this work is directed to optimize the PSCs based on Sn perovskites. The optimization has been done through the effects of inverted structure, type of hole transporting layer material, and different kinds of electrodes. The optimization investigation is processed by simulation using advanced software. These techniques of investigation offer a range of advantages that can accelerate research, improve device performance, and reduce costs. The advantages of optimizing PSCs theoretically include testing various configurations, materials, and parameters virtually, which reduces the need for expensive and time-consuming experimental trials. Furthermore, by optimizing the design and materials through simulations, the amount of material waste in the experimental phase is minimized. Also, simulations can precisely tune parameters such as layer thickness, material compositions, and interface properties to achieve optimal device performance.
The performance of solar cells was investigated using the commercial software SETFOS, which is based on numerical simulation. It can simulate and optimize the optical and electrical properties of both perovskite and organic devices. Utilizing SETFOS enables a comprehensive understanding of the physics of optical materials, facilitates the refinement of experimental techniques, and optimizes technological parameters to enhance the performance of optoelectronic devices such as light-emitting diodes and solar cells. Many researchers have used and validated this software for PSC simulation^28,29,30,31.
We have selected SETFOS due to its built-in multi-physics modules, which enable accurate simulation of the charge transport and optical phenomena.
It efficiently models light effects, exciton diffusion, recombination, and light management effects, providing comprehensive insights into the electrical properties of solar cells and other optoelectronic devices. Additionally, the embedded parameters in this software allow for simultaneous variation of multiple parameters, facilitating the optimization of the performance of the solar cell. SETFOS also offers easy data extraction, and a user–friendly interface, making it highly accessible for researchers.
Initially, the PSC structure that consists of Glass/ ITO/ TiO2/ CH3NH3SnI3/ ZnTe /Au shown in Fig. 1 was simulated. The obtained relationship between solar cell current density and voltage is shown in Fig. 2. By analyzing the J-V curve, the key performance metrics such as J_sc, V_oc, FF, and efficiency were determined as shown in Table 1. The results were compared to experimental data published by Kumari K, et al.³².
Solar cells based on perovskite material composed of Glass/ ITO/ TiO₂/ CH₃NH₃SnI₃/ ZnTe / Au.
Validation of simulation results against experimental data for CH₃NH₃SnI₃ perovskite solar cells.
It is evident that the simulation’s outcomes fairly match the experimental data, proving the model’s accuracy and applicability in scientific settings. With the accuracy of our method now, we can optimize the cell’s performance by varying the thicknesses and adding transporting layers.
The solar cell based on CH₃NH₃SnI₃ was examined by replacing the ZnTe with 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) as a hole transport layer (HTL) to increase the efficiency of this regular structure as shown in Fig. 3. TAPC is a nonhazardous, widely used material in organic light-emitting diodes (OLEDs) and perovskite solar cells³³. It can easily be deposited as a hole transporting layer using a thermal evaporation or solution processing technique^34,35,36.
Solar cells based on perovskite material composed of Glass/ ITO/ TiO₂/ CH₃NH₃SnI₃/ TAPC / Au.
We have used the same thickness of ZnTe for TAPC (250 nm) to test the efficiency improvement. By making this change, we achieved better PCE and FF as shown in Table 2. The V_oc slightly decreased, whereas PCE, and FF showed a pronounced increase. The efficiency increased by about 34.92% relative to the device based on ZnTe, but we should keep in mind the stability issue. Using TiO₂ as electron transport layers (ETLs) in n-i-p PSCs is prone to UV-induced photocatalytic reactions. These reactions can break down the perovskite layer over time, contributing to efficiency loss. TiO₂ under UV light can generate reactive oxygen species, which degrade the perovskite material³⁷. To overcome this problem, the inverted structure was designed and investigated.
To build an inverted arrangement, ETL and HTL positions were switched to make an inverted p-i-n structure. In this case, TiO₂ becomes behind the active perovskite layer and not on the direct path of incident light. In this way, we avoid the above-mentioned shortcomings. However, a top electrode with a higher work function is now required. Previously, ITO served as the cathode in contact with TiO₂. The work function of ITO (-4.7 eV) was well aligned with the conduction band level of TiO₂ (-4.26 eV), enabling efficient electron transport. However, when switching to a p-i-n structure, the hole-transporting layer TAPC is now in contact with the top electrode. TAPC has a higher HOMO level (-5.5 eV), meaning the top electrode must possess a higher work function to align properly with TAPC and minimize the potential barrier for a better hole transport. A hybrid electrode composed of ITO/PEDOT: PSS offers a promising solution. PEDOT: PSS has an intrinsic work function of approximately − 5.2 eV, which aligns more closely with the HOMO level of TAPC (-5.5 eV). This improved band alignment facilitates more efficient hole transport. While ITO alone has a lower work function, the combination of ITO with PEDOT: PSS increases the overall work function, making it a better match for TAPC³⁸. Therefore, we used ITO/PEDOT: PSS as the top electrode. By moving TiO₂ to the second direction below the Au electrode, another challenge arises due to the high barrier between the Au Fermi level and the conduction band edge of TiO₂. To overcome this problem, Au was replaced with Al, which possesses a low work function that aligns well with the conduction band level of TiO₂ (-4.26 eV). Using aluminum (Al) has two benefits; besides lowering the barrier, it’s considered economical. With these modifications, the complete inverted structure composed of Glass/ ITO/ PEDOT / TAPC/ CH₃NH₃SnI₃/ TiO₂/Al is designed. This inverted structure improved the fill factor; however, it slightly reduced device current and PCE, as shown in Table 3.
We attribute the lack of improvement in efficiency to this design to the high thickness of TAPC and PEDOT layers (unoptimized thickness), resulting in optical resonance, carrier recombination, and other factors causing the decrease in device efficiency. To confirm our interpretation, the effect of PEDOT and TAPC thicknesses on the absorption of the active layer was investigated as shown in Fig. 4. Clearly, the thicker layers of TAPC and PEDOT reduce the absorption properties of the active layer. In contrast, optimized thinner layers, the active layer, have shown better absorption. For example, reducing the TAPC layer to 120 nm increases absorption for wavelengths between 500 nm and 600 nm, broadening the absorption range. Likewise, a thinner PEDOT layer (5 nm) greatly increases absorption at wavelengths between 440 nm and 556 nm; additional enhancement and widening is shown beyond 613 nm. This improvement is primarily attributed to the reduction in parasitic absorption (Fig. 5) and the optimization of optical interference conditions. Moreover, small thickness also improves charge extraction by reducing the distance charged carriers must travel before reaching the electrodes, thereby lowering the likelihood of recombination losses.
Light absorption in the active layer for varying thicknesses of the PEDOT and TAPC layers. (a) Comparison between PEDOT thickness of 5 nm and 100 nm; (b) Comparison between TAPC thickness of 120 nm and 250 nm.
Variation of the device efficiency and absorption of PEDOT with the different thickness of the PEDOT. (a) Variation in efficiency with different PEDOT thickness; (b) Absorption by the PEDOT layer for the thickness of 5 nm and 100 nm.
Therefore, we have proceeded to optimize the layer thicknesses of the proposed configuration along with adding a buffer layer of NiO (10 nm) underneath the CH₃NH₃SnI₃ layer to decrease any interface recombination and give more stability to the active layer. Insertion of NiO causes a reduction in the FF and PCE with little increase in the device current and voltage, as shown in Table 4. Therefore, NiO thickness also requires optimization to improve efficiency.
The main reason for the drop in fill factor (FF) and power conversion efficiency (PCE) is that the series resistance elevated from 0.31 Ω·cm² to 3.93 Ω·cm² when the NiO buffer layer was added. The NiO layer makes it easier for carriers to be extracted at the interfaces, which leads to higher V_oc and J_sc values. These values are determined under open-circuit and short-circuit conditions, which are not significantly affected by series resistance. However, under load, the increased resistance causes significant voltage drops, which reduces the FF and overall PCE.
The effect of variation in the thickness of the active layer on PCE and V_oc was investigated. As we can see in Fig. 6-(a, b), the PCE reaches a maximum value at around 100 nm of the active layer and then saturates with no further increase. Whereas V_oc shows a sharp decrease at a small thickness below 100 nm, remains relatively stable between 100 nm and 250 nm, then shows a slight decrease with a further increase in thickness beyond 250 nm. The balance between light absorption and recombination of charge carriers largely determines the maximum voltage achievable under illumination. When the active layer is thinner than about 100 nm, it absorbs significantly less light, as shown in Fig. 6-(c). As we can see, until 100 nm, the absorption properties of the active layer vary significantly. At a lower thickness, it absorbs very few photons. Which means fewer electrons and holes are generated. Reduced generation of carriers leads to small output voltage.
Changes in device efficiency, V_oc and active layer absorption with the variation of CH₃NH₃SnI₃ thickness. (a) Effect of CH₃NH₃SnI₃ film thickness on power conversion efficiency (PCE); (b) Variation of open-circuit voltage (V_oc) with CH₃NH₃SnI₃ film thickness; (c) Changes in absorption properties for different film thickness of CH₃NH₃SnI₃.
Based on these outcomes, we have selected an active layer thickness of 200 nm for further study; with the selection of this thickness, the V_oc and device efficiency are improved, as displayed in Table 5.
The effect of the thickness of ITO is also investigated on the absorption of the active layer and power conversion efficiency, as shown in Fig. 7. The effect of variations of ITO thickness from 5 nm up to 200 nm on the absorption of the active layer was investigated. As shown in Fig. 7a, b, and c, the variation of ITO thickness revealed two regions of high absorption of the active layer. One of the maximum absorptions of the active layers is located in the blue light region, and the second broad maximum is located at the middle of the visible region. To completely decide which range of thickness gives the highest performance, the effect of ITO thickness on power conversion efficiency was investigated as shown in Fig. 7d. The variation of a thickness at small values shows a sharp decline in power conversion efficiency (PCE) with a dip around 70 nm, followed by an abrupt increase in PCE as the thickness increases up to 135 nm. It is well known that changing the ITO thickness can affect various parameters, including transparency, sheet resistance, refractive index, anti-reflection effect, carrier mobility, conductivity, work function, and energy band alignment. The combined influence of these factors may explain why there is no clear trend in the variation of active layer absorption and PCE with changing ITO thickness. Part of our future work will be directed toward studying the effect of varying the thickness of ITO on the performance of the perovskite solar cell by analyzing changes in all the above parameters.
Variation in active layer absorption (a, b, c) and device efficiency (d) with the different thickness of ITO.
In the range of thickness from 135 nm to 190 nm, the PCE stabilizes with slight oscillation at higher values. The oscillation combined with a marginal increase in PCE. Beyond 190 nm thickness of ITO, the performance starts to decrease, followed by an enhancement. These results motivated us to select an ITO thickness of 190 nm for further study, as shown in Table 6. We didn’t select a small thickness that gives a high efficiency because the very small thickness may develop non-uniformities or pinholes in the ITO layer, which could increase light scattering or cause short circuits in some cases.
The effect of PEDOT thickness on the performance is simulated, as shown in Fig. 5. Clearly, as the PEDOT thickness increases, the PCE steadily decreases. The curve starts at a relatively high PCE and declines smoothly as the thickness increases. This indicates that increasing the PEDOT thickness negatively affects the solar cell’s efficiency, likely due to reduced light transmission or hindered charge collection. Consequently, a thinner PEDOT layer is more favorable for achieving higher efficiency. This suggests confirmed by the investigation of the absorption of PEDOT as shown in Fig. 5b. Clearly, the absorption of PEDOT increased significantly for larger thickness in comparison with smaller thickness. Based on these findings, we selected a PEDOT thickness of 5 nm. Applied this value, we found that the efficiency significantly improved, as shown in Table 7.
The effect of variation of TAPC thickness on the performance of the designed cell is investigated. Figure 8 shows the variation in PCE against TAPC thickness up to 200 nm. The effect of TAPC thickness variation shows a symmetrical hump of PCE increases with a higher maximum around 120 nm. Based on this observation, a TAPC thickness of 120 nm was selected for further investigation. By applying the selected thickness of TAPC, the cell efficiency and current increase, as displayed in Table 8.
Changes in device efficiency with the variation of TAPC thickness.
The optimization of the thickness of NiO is investigated. Figure 9 shows the effect of variation of NiO on the PCE. Initially, the PCE is relatively high, and it reaches its peak at approximately 5 nm. Beyond this point, the PCE steadily declines as the NiO thickness increases. This pattern suggests that thinner NiO layers, particularly around 5 nm, are optimal for achieving the highest PCE. Increasing the NiO thickness beyond 5 nm negatively impacts efficiency, likely due to reduced light transmission or poor charge extraction. By selecting a 5 nm NiO thickness, we were able to significantly improve the solar cell’s efficiency and enhance the fill factor, contributing to better device performance, as shown in Table 9.
Changes in device efficiency with the variation of NiO thickness.
The effect of variation of the thickness of the electron transporting layer TiO₂ is simulated. Figure 10 displays the variation of PCE against TiO₂ thickness. PCE initially increases sharply, reaching a first peak at around 58 nm; beyond this thickness, the PCE decreases slightly but rises again to a similar maximum peak at approximately 110 nm. Further increasing of the thickness beyond 110 nm causes the PCE to a sharp decline and drop to a much lower value around 200 nm. This pattern suggests that there are two optimal thicknesses of 58 nm and 110 nm, where the PCE is maximized. Increasing the TiO₂ thickness beyond these points results in a significant drop in efficiency. Based on this observation, the TiO₂ thicknesses of 58 nm and 110 nm represent favorable choices for achieving high efficiency. However, given the more significant peak at 110 nm, we chose this thickness for further study, as it represents the point where the solar cell achieves the highest efficiency, as shown in Table 10.
Changes in device efficiency with the variation of TiO₂ thickness.
Table 11 shows the summary of our overall device optimization. The V_oc, J_sc, FF, and PCE data show that the solar cell’s performance significantly improved after the parameters were optimized through a series of optimizations. First, the replacement of ZnTe with TAPC contributed to a noteworthy 34.92% rise in PCE, primarily due to a 44% enhancement in FF; however, V_oc experienced a 6.33% decline. When the structure was inverted, the V_oc did not change, but J_sc dropped by 8.26%, which resulted in a minor loss in PCE of 8.60% despite small gains in FF. Adding a buffer layer resulted in an improvement in V_oc by 5.41% and J_sc by 10.87%. However, the FF decreased by 15.96%, which led to a slight decline in PCE of 1.84%. Lastly, thickness optimization produced a pronounced enhancement in the performance, improving V_oc (2.56%), J_sc (7.14%), and FF (11.32%) to produce a 22.20% rise in PCE.
TAPC has relatively high hole mobility, which helps in the efficient transport of photogenerated holes from the active layer to the electrode. Efficient hole extraction is crucial for reducing charge recombination losses, thus increasing the overall power conversion efficiency (PCE) of the solar cell. Accordingly, the PCE increased by around 34.92% when TAPC was used instead of ZnTe as an HTL. This is because the band alignment of TAPC fits better with CH₃NH₃SnI₃ compared to ZnTe, as shown in Fig. 11. This band alignment causes efficient charge extraction and reduces series resistance, allowing for higher fill factors by improving current-voltage characteristics and minimizing recombination losses. Moreover, TAPC has a higher LUMO level (~ -2 eV) than ZnTe (~ -3.73 eV), which makes TAPC better at electron blocking. This higher LUMO level of TAPC forms a substantial energy barrier for electrons and consequently lowers the loss of carriers through recombination at the interface.
Energy band alignment of: (a) PSC structure with ZnTe as a hole transporting layer; (b) PSC structure with TAPC as a hole transporting layer.
To better understand the effect of replacing ZnTe by TAPC, we have investigated the series resistance (R_s) for both arrangements. By applying the Lambert W-function to the J–V curves, we obtained an R_s of ~ 9.74 Ω·cm² for the cell based on ZnTe and ~ 1.14 Ω·cm² for the cell based on TAPC. Applying TAPC as an HTL greatly reduces the overall series resistance, leading to enhancement of efficiency by 34.92% as we mentioned earlier. Moreover, the recombination rate was investigated for the two configurations of the cells as shown in Fig. 12. Obviously, the recombination rate significantly reduced for the cell based on TAPC compared to that based on ZnTe .
Recombination rate profiles simulation for devices based on ZnTe (left) and TAPC (right) as the hole transport layer (HTL) (Note: the light is incident from left side of the cell). The x-axis represents the layer thickness, with the active layer of 400 nm, while the y-axis shows the applied voltage (0–1.5 V). The color scale indicates the recombination rate (cm⁻³ s⁻¹), ranging from 10¹⁰ (purple) to 10²² (red). The cell based on TAPC exhibits more purple and blue regions, indicating lower recombination—compared to the cell based on ZnTe, which shows small area of purple color and extended area of red color.
In the aforementioned structure, TiO₂ was used as an electron transport layer. TiO₂ has a wide band gap(~ 3.2 eV), making it an efficient electron transport and hole-blocking material. However, TiO₂ has some absorption contributions in the visible spectrum, as shown in Fig. 13. So, when using TiO₂ in the n-i-p structure, it is located on the top of the perovskite layer in the path of light radiation. This reduces some of the visible light going into the perovskite layer, thus reducing the overall efficiency. Furthermore, TiO₂ can lead to photo-degradation of the perovskite layer over time upon UV exposure³⁹. Accordingly, placing TiO₂ away from the path of light underneath the perovskite layer could enhance the cell’s overall performance. The possible way to place the electron transporting layer below the active layer is switching n-i-p structure into a p-i-n inverted structure, as shown in Fig. 14.
Light absorption of different configurations. (a) Absorption of n-i-p configuration; (b) Absorption of p-i-n configuration.
(a) Inverted layer structure, and (b) energy band alignment, of perovskite solar cells based on CH₃NH₃SnI₃ as the active layer.
Accordingly, we have designed a p-i-n structure consisting of Glass/ ITO/ PEDOT / TAPC/ CH₃NH₃SnI₃/ TiO₂/ Al. In this flip structure, we have added a PEDOT buffer layer between TAPC and ITO, alongside the replacement of Au with an Al electrode. Herin the insertion of PEDOT between ITO and TAPC could reduce the hole-injection barrier. This enhanced injection improves charge transport, which can increase the overall current density and efficiency of the cell. Moreover, the mechanical flexibility of the ITO electrode could improve by adding a PEDOT: PSS buffer layer without sacrificing its electrical or optical qualities. According to previous investigation, the hybrid electrode excels in bending stress resistance, exhibiting little change in electrical resistance even when bent below 3.5 mm, and exhibits a significant reduction in sheet resistance from 230 Ω/sq to 85 Ω/sq⁴⁰. The PEDOT: PSS/ITO hybrid electrode shows excellent stretchability in fragmentation experiments, showing no cracks at a substrate strain of 4%. This strong performance is attributed to the improved interfacial adhesion strength and break resistance provided by the PET (polyethylene terephthalate) substrate. Furthermore, the hybrid anode in organic photovoltaic (OPV) devices yields a noteworthy 3.21% power conversion efficiency, which is on par with single-layered ITO anodes⁴⁰.
For inverted-structure Perovskite Solar Cells (PSCs), aluminum (Al) is the best material for the bottom electrode because of its excellent electrical conductivity and affordability. Aluminum’s low work function is especially useful in the unique situation of PSCs with inverted structures. The work function of Al (~ 4.2 eV) aligns well with the conduction band of TiO₂ (~ 4.26 eV), facilitating effective electron transfer from the TiO₂ (ETL) to the Al electrode. This matching minimizes energy loss at the interface, enhancing overall charge extraction and reducing recombination, which supports a higher fill factor and efficiency in the solar cell⁴¹.
Incorporating NiO as a hole selective layer (HSL) resulted in yet another noteworthy advancement. Research indicates that as the thickness of NiO increases beyond a few nanometers, its insulating qualities rise. Strong bonds found in thick layers of NiO limit the mobility of ions and charge carriers⁴². In addition, thick NiO can increase the resistance at interfaces and reduce the open-circuit voltage (V_oc), ultimately impacting the cell’s performance. Oppositely, the thin thicknesses of NiO films as an HSL have been reported in the range between 15 and 20 nm^43,44,45. In this range of thickness of NiO the holes can move more freely to the electrode, consequently, the charge collection increases. Higher electrical conductivity can be achieved by using NiO as ultrathin films with high conformality. Furthermore, thin NiO layer reduces the number of defect sites and traps that can form within the material, lowering the chances of charge recombination at the interface with the absorber layer. Also, in a solar cell, the Debye length is critical because it dictates how well the NiO layer can transport holes to the electrode while maintaining separation of charges. If the NiO layer thickness exceeds the Debye length, ion screening can be inefficient, increasing recombination losses. The Debye length and the film thickness requirements ought to be equivalent. In a different study, the Debye length (LD) overlap increases photovoltaic characteristics and appears to boost NiO’s work function and hole concentration when the film thickness becomes extremely thin⁴⁶. The investigation of the NiO optical film thickness of the designed cell compatible with all previous study by providing an optimal NiO thickness of 5 nm for improved performance of PSC. Consequently, the thinnest NiO layer is effective for hole extraction and avoids the drawbacks of thicker films, such as increased resistance.
The final optimized perovskite solar cell (PSC) structure, ITO(190 nm)/PEDOT(5 nm)/TAPC(120 nm)/NiO(5 nm)/CH₃NH₃SnI₃ (200 nm)/TiO₂(110 nm)/Al(100 nm), shows substantial improvements in performance parameters (Fig. 15), demonstrating significant advancements over previous designs. The achieved Open-Circuit Voltage (V_oc) of 0.80 V, Short-Circuit Current Density (J_sc) of 18.34 mA/cm², Fill Factor (FF) of 84.28%, and Power Conversion Efficiency (PCE) of 12.37%. The obtained solar cell key metrics of the designed cell with applying TAPC hole transporting layer showed a significant improvement compared to the previous study³². The optimized inverted structure and modified regular configuration reveals a marked improvement in all metric parameters, particularly in FF and PCE. The increased fill factor suggests enhanced interface quality and minimized resistive losses, while the notable increase in PCE demonstrates the effective layer-by-layer optimization. These enhancements confirm the effectiveness of careful layer selection and thickness optimization in PSC design, making this structure a promising candidate for efficient and stable perovskite solar cells.
(a) J-V characteristics, and (b) Power Conversion Efficiency (PCE), of our CH₃NH₃SnI₃ perovskite solar cells.
Our comprehensive investigation into enhancing the efficiency of perovskite solar cells (PSCs) has yielded several significant findings and optimizations. Substituting ZnTe with TAPC polymer as a hole transport layer (HTL) resulted in a notable increase in power conversion efficiency (PCE) by approximately 34.92%. This enhancement can be attributed to the superior band alignment of TAPC with CH₃NH₃SnI₃, as well as its higher LUMO level compared to ZnTe, facilitating better electron blocking. Transitioning from a n-i-p structure to a p-i-n inverted structure, along with relocating TiO₂ to the bottom of the perovskite layer, demonstrated enhanced efficiency by allowing more light to reach the perovskite layer, thereby increasing device current. Additionally, integrating NiO as a hole-selective layer (HSL) and the overall thickness optimization contributed to a further increase in PCE, along with improvements in short-circuit current density (J_sc) and open-circuit voltage (V_oc).
Through systematic optimizations and structural modifications, we have significantly improved the performance of PSCs, paving the way for more efficient and cost-effective solar energy harvesting technologies. These findings offer valuable insights for the continued development and advancement of perovskite-based photovoltaic devices.
All data generated or analysed during this study are included in this published article.
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The authors extend their appreciation to the Deputyship for Research& Innovation, Ministry of Education in Saudi Arabia for funding this research work through the project number (1003).
Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
Qana A. Alsulami
Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah, 21589, Saudi Arabia
Rasul Al Foysal Redoy & S. Wageh
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Conceptualization, A. Al. R., Q.A.A., and S. W.; methodology, A. Al. R., and S. W.; software, A. Al. R. and S. W.; validation A. Al. R. Q.A.A. and S. W.; formal analysis, Q.A.A., Al. R. and S. W.; investigation, A. Al. R., Q.A.A., and S. W.; data curation, A. Al. R., Q.A.A., and S. W.; writing—original draft preparation, Q.A.A., and A. Al. R.; writing—review and editing, S. W.; visualization, A. Al. R., Q.A.A., and S. W.; ; supervision, S.W.; project administration, S. W and Q.A.A.; funding acquisition, Q.A.A. A.
Correspondence to S. Wageh.
The authors declare no competing interests.
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Alsulami, Q.A., Redoy, R.A. & Wageh, S. Efficiency optimization of lead-free CH₃NH₃SnI₃-based perovskite solar cells through material and structural modifications. Sci Rep 15, 13170 (2025). https://doi.org/10.1038/s41598-025-95473-1
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Received: 11 November 2024
Accepted: 21 March 2025
Published: 16 April 2025
Version of record: 16 April 2025
DOI: https://doi.org/10.1038/s41598-025-95473-1
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