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Scientific Reports volume 15, Article number: 42865 (2025) Cite this article
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This study examines the efficiency enhancement of lead-free perovskite solar cells using a dual absorber layer design. Through Solar Cell Capacitance Simulator in One Dimension (SCAPS-1D), the performance of a CsSnGeI₃/CsGeI₃ heterojunction with a Cu₂O hole transport layer under AM1.5G illumination is evaluated. Key factors analyzed include absorber layer thickness, doping concentration, defect density, temperature, series resistance, and shunt resistance. The results reveal that the dual absorber design with the structure FTO/SnS₂/ CsGeI₃/CsSnGeI₃/Cu₂O/Au significantly improves the power conversion efficiency to 34.18%, achieving a short-circuit current density of 32.67 mA/cm², open-circuit voltage of 1.25 V, and fill factor of 83.64%. Each absorber layer is optimized to a thickness of 0.8 μm, leading to superior performance compared to single-layer perovskite solar cells (PSCs). The optimal doping concentrations are approximately 1 × 10¹⁷ cm⁻³ for CsGeI₃ and 1 × 10¹⁶ cm⁻³ for CsSnGeI₃, while the defect densities are minimized to about 1 × 10¹² cm⁻³ for both layers. Furthermore, maximum efficiency is achieved by optimizing additional key parameters, including an operating temperature of 300 K, and a series resistance of 0 Ωcm². This improvement stems from a broader absorption spectrum and enhanced charge separation facilitated by the heterojunction. The study provides critical insights into dual absorber configurations for advancing PSC photovoltaic performance.
The global reliance on fossil fuels has raised serious environmental concerns and significantly contributed to the acceleration of climate change¹. To address this pressing issue, it is crucial to expand the use of clean and sustainable energy sources, such as thermoelectric power, wind energy, and photovoltaic (PV) technology, which offer environmentally friendly solutions for meeting growing energy demands^2,3,4. Among these alternatives, PV technology stands out due to the widespread availability of solar radiation and its ability to convert sunlight directly into electricity in a clean and efficient manner⁵. Solar cells, typically composed of P-type and N-type semiconductors, enable this direct energy conversion^6,7,8. Although silicon-based PV systems currently dominate the market, their cost remains a barrier to adoption in economically disadvantaged regions.
Perovskite solar cells (PSCs) represent a highly promising and innovative advancement in photovoltaic (PV) technology, distinguished by their cost-effectiveness and remarkable efficiency. Moreover, their potential for scalable production makes them an ideal solution for addressing the energy requirements of economically disadvantaged communities, enabling access to sustainable and affordable power sources^9,10,11. However, a significant challenge for PSCs lies in their stability, both thermally and mechanically. Consequently, efforts have been made to enhance PSC efficiency, leading to a significant improvement from 3% in 2006 to approximately 20% by 2020^{12,13,14,15,16}. Earlier investigations have explored the use of organic materials in PSC construction, laying the groundwork for future device development. The bandgap is a critical parameter, as it defines the minimum energy required for incident photons to be absorbed¹⁷, and perovskite materials offer the unique advantage of tunable bandgaps through compositional engineering, thereby directly influencing their absorption coefficient¹⁸. Unlike silicon solar cells, perovskites are often straightforward and inexpensive to fabricate. Despite the high efficiency of the PSCs, many of them still rely on corrosive and toxic compounds like lead, methylammonium (MA) and formamidinium (FA)^19,20,21,22.
The rationale behind selecting these specific structures lies in their potential to optimize photon absorption and charge transportation properties. The selection of eco-friendly materials such as CsGeI₃ and CsSnGeI₃ aims to cover a broader portion of the solar spectrum while maintaining favorable band configuration and effective charge separation. Recent research has explored the development of Pb-free PSCs with reduced corrosiveness and toxic elements in the absorber layer, such as Cs₂GeSnCl₆ ²³, Cs₂GeSnBr₆ ²⁴, CsSnI₃ ²⁵, and A₂NiMnO₂ ²⁶. CsGeI₃ and CsSnGeI₃ possess several remarkable properties that make them promising candidates for lead-free perovskite absorbers. CsGeI₃ offers a direct bandgap (1.363 eV), excellent thermal stability, and low toxicity, making it suitable for stable device architectures^{27,28,29,30,31}. Similarly, CsSnGeI₃, a mixed tin-germanium iodide perovskite, exhibits a tunable bandgap, high absorption coefficient, and improved defect tolerance, allowing efficient light harvesting across a broad spectrum^32,33,34,35. Despite its potential, CsGeI_xBr_3−x perovskite material has received limited attention, even though it offers a tunable band gap and notable thermal stability up to 350 °C³⁶. Miah and his research group conducted simulations on an innovative design involving Pb-free CsGeI₃-based all-inorganic PSCs. Applying MnO₃ as the hole transport layer (HTL), the researchers utilized SCAPS-1D (Solar Cell Capacitance Simulator in One Dimension) software and achieved an efficiency of 22.85%. Their findings indicated that the back contact electrode’s work function falls inside the boundary of 5 eV to 5.7 eV. Additionally, they determined that the optimal defect density is about 10¹² cm⁻³³⁷.
In our PSC architecture, SnS₂ is employed as the electron transport layer (ETL) due to its excellent electron mobility, wide bandgap (2.24 eV)³⁸, and favorable conduction band alignment with the perovskite absorbers, which facilitates efficient electron extraction and suppresses recombination³⁹. On the other hand, Cu₂O is selected as the HTL because of its high hole mobility, suitable valence band alignment, good chemical stability, and non-toxic, earth-abundant nature^40,41.
In this study, we propose a novel lead-free hybrid PSC structure based on a CsSnGeI₃/CsGeI₃ double-absorber heterojunction, which, to the best of our knowledge, has not been previously explored. The primary objective is to optimize photovoltaic performance through structural innovation and device parameter tuning. To achieve this, we employ a simulation-based approach using SCAPS-1D software to systematically investigate the influence of key parameters, including absorber layer thickness, doping concentration, and defect density. Furthermore, we evaluate the effects of temperature variations, and series resistance on device output characteristics. This work aims to provide design insights into next-generation, environmentally friendly PSCs by combining material innovation with simulation-based optimization strategies.
Three HTL-based PSC designs utilize distinct light-absorbing substances: a CsSnGeI₃, b CsGeI₃, and c a bilayer comprising of CsSnGeI₃/CsGeI_3, respectively.
Researchers utilize the SCAPS-1D software to adjust various parameters essential for photovoltaic performance. These tasks include adjusting absorber material thickness, doping concentrations, selecting front and rear contact materials, defining operating temperatures, improving quantum efficiency, and fine-tuning J–V parameters, among other optimizations. SCAPS-1D is a specialized simulation tool developed for solar cells, operating under one-dimensional conditions. The development was carried out by the Department of Electronics at Ghent University in Belgium⁴², SCAPS-1D employs important equations such as the Poisson and continuity equations to model electron-hole interactions accurately. The simulations in this research are conducted under an AM1.5G spectrum with a power density of 0.001 W/mm². The research involves evaluating and comparing the performance of three different device structure using SCAPS-1D. The device designs, labeled as FTO/SnS₂/CsSnGeI₃/Cu₂O/Au, FTO/SnS₂/CsGeI₃/Cu₂O/Au and the optimized device is FTO/SnS₂/CsSnGeI₃/CsGeI₃/Cu₂O/Au depicted in Fig. 1a–c.
In this study, FTO is used as the front contact layer, and SnS₂ acts as the electron transport layer (ETL). Gold (Au, with a 5.2 eV work function) is employed as the rear contact, while aluminum (Al, with a 4.2 eV work function) is chosen as the front metal contact due to its high electrical conductivity, strong chemical stability, and suitable work functions. These properties facilitate efficient hole extraction from the Cu₂O layer and help reduce energy losses^43,44. SnS₂ is selected due to its superior carrier mobility and favorable band configuration with the absorber materials. Cu₂O is selected as HTL. The thickness of SnS₂ and Cu₂O are determined to be 0.05 μm, while the thickness of absorber layers is varied. Solar cell operation involves three primary processes: light absorption, separation of electric charges, and extraction of these charges to their respective electrodes, followed by their transfer to external devices. The chosen materials facilitate electron migration from the absorber’s conduction band to the front contact FTO through the SnS₂ ETL, while holes are directed from the absorber’s valence band toward the rear contact layer consisting of Au. The input parameters which are applied as input for the various regions of the three structures are mentioned in Tables 1, and 2.
In this study, the heterojunction PSC was simulated using version 3.3.11 of the SCAPS-1D software⁴². Through optimization techniques and exploration of the PSCs, successful completion of the simulation was achieved. SCAPS-1D operates on numerical techniques, solving semiconductor equations. The framework relies on three interconnected differential equations, numerically solving the continuity equation and Poisson’s formula for both hole and electron charge carriers (Eqs. (1)–(3))^12,49.
In these equations, the terms represent various parameters such as electrostatic potential (ϕ), elementary charge (q), permittivity in free space (ε₀), relative permittivity (ε_r), concentrations of electron (n) and hole (p), density of acceptor (N_A) and donor (N_D), trapped concentrations of electron (n_t) and hole (p_t), recombination rates of electrons (R_n) and holes (R_p), and creation rate of electron (G_n) and hole (G_p). J_n and J_p signify the density of electron and hole current, respectively which are defined in Eqs. (4) and (5), respectively. Parameters such as electron and hole mobility, diffusion coefficient of holes and electrons are represented by µ_n, µ_p, D_n, and D_p, respectively^50,51.
While SCAPS-1D provides a valuable platform for simulating the performance of perovskite solar cells, it does have certain limitations. The model assumes ideal interfaces and does not account for interface recombination, grain boundary effects, or long-term material degradation, which can significantly impact real-world device performance⁵². Furthermore, the simulations are one-dimensional and neglect lateral effects, which are important in large-area devices. Therefore, while the results offer useful insights into trends and optimization strategies, experimental validation is essential to confirm the practical applicability of the proposed design, and the insights gained from this study can effectively inform and guide future experimental research in PSC development.
This segment delves into the results of multiple factors on the output of the device metrics, specifically J_SC, V_OC, FF, and PCE. These factors contain active layer thickness, doping density, defect density, temperature, rear contact metal, and series resistance. The study is meticulously organized into subsections, each providing an in-depth analysis of these individual elements and their impact on the device’s efficiency and functionality.
Figure 2a–c demonstrate the band diagram of CsSnGeI₃, CsGeI₃, CsSnGeI₃/CsGeI₃ bilayer-based PSCs, providing an inclusive overview of their behavior. In this background, the signs E_V, F_P, F_n, and E_C denote different energy states within the band configuration, specifically signifying the maximum energy level of the valence band (VB), the holes Fermi level, the electrons Fermi level, and the minimum energy level of the conduction band (CB), respectively.
The band alignment for PSCs with a CsSnGeI₃, b CsGeI₃, and c a bilayer comprising of CsSnGeI₃/CsGeI₃ absorber, respectively.
The variation in energy levels between the lowermost point of the CB in the absorber layer and the CB edge of the ETL is termed the conduction band offset (CBO). Likewise, the energy difference between the uppermost point of the VB in the absorber layer and the VB edge of the HTL is referred to as the valence band offset (VBO). In this investigation, the energy gaps of CsSnGeI₃ and CsGeI₃ perovskite materials are measured at 1.5 eV and 1.363 eV, respectively. The energy bandgap of the fluorine-doped tin oxide (FTO) window layer is measured to be 3.6 eV, though the n-type tin disulfide (SnS₂) buffer layer and the HTL exhibit energy bandgaps (E_g) of 2.24 eV and 2.17 eV, respectively. Figure 2c illustrates that the CB of CsGeI₃ resides at an energy level above that of CsSnGeI₃, allowing electrons to flow from CsGeI₃ to CsSnGeI₃. This energy difference facilitates efficient electron transfer to the ETL. Conversely, the VB of CsGeI₃ is higher in energy than that of CsSnGeI₃, enabling holes to flow from CsSnGeI₃ to CsGeI₃, thus promoting efficient hole transfer to the HTL⁵³. At the same time, dual absorber PSC covers wider range of the solar spectrum by utilizing two different energy bandgaps which enhances the overall efficiency compared to the single absorber PSCs.
The combined effect of the dual perovskite active layer (PAL) thickness represents in the contour analysis of Fig. 3 which provides valuable insights into performance of the PSC device. The horizontal-axis signifies the thickness of CsGeI₃, while the CsSnGeI₃ thickness is demonstrated on the vertical-axis.
The photovoltaic parameter a J_SC. b FF. c V_OC, and d PCE are analyzed by varying the thickness of the perovskite active layer (PAL).
The simulation model employed in this research involved varying the thicknesses of active layers from 100 nm to 1000 nm. This innovative method, as displayed in Fig. 3a–d, demonstrate a means to assess influence of thickness. It is seen that the V_OC reaches its highest value with thinner PAL thicknesses, achieving up to 1.25 volts, but decreases with rising PAL thickness owing to enhanced rates of recombination by introducing more defect⁵⁴. Regarding the J_SC, a CsGeI₃ thickness of almost 1 μm gives better results, giving up to 33.25 mA/cm². On the contrary, lesser thickness of CsGeI₃ and CsSnGeI₃ result in decreased J_SC for insufficient absorption of photon within the PALs⁵⁵, attaining about 21.40 mA/cm², thus impacting efficiency negatively. The contour diagram in Fig. 3c reveals that a double PAL PSC offers a highest FF of 83.78% at optimal thickness. Ultimately, the combined influence of the thicknesses of the PAL on the PCE is illustrated in Fig. 3d. The analysis reveals that an optimal PCE of 34.18% is achieved when both CsGeI₃ and CsSnGeI₃ layers are precisely maintained at a thickness of 0.8 μm.
The active layer of the perovskite material captures photons of light, producing electron-hole pairs. Carrier concentration can be enhanced by doping this layer, and bending the energy diagrams of the heterojunction can align them with the ETL, thereby improving solar cell performance. We investigate the outcome of acceptor concentration (N_A) change in the CsGeI₃ and CsSnGeI₃ layers, extending from 1 × 10¹² to 1 × 10¹⁹ cm⁻³. Figures 4a–d explain the effect of doping on the output of the PSCs. It was observed that this PSCs reveals better performance when the doping in the CsGeI₃ layer surpasses that in the CsSnGeI₃ layer, as shown in Fig. 4d.
Indeed, when the level of doping density in CsGeI₃ layer exceeds that of the CsSnGeI₃ layer, it improves the hole and electron mobility in the active layer. The FF is significantly influenced by variations in doping concentration, as demonstrated in Fig. 4b. The changes of doping in the active layer generates an internal electric field, leading to a significant emission of electrons from the device, as depicted in Fig. 4a. Subsequently, as a result of this phenomenon the voltage is reduced, which depicted in Fig. 4c.
Influence of active layer doping on the output of PSCs: a J_SC. b FF. c V_OC. d PCE.
Instead, as the doping in the CsSnGeI₃ layer exceeds that of the CsGeI₃ layer, then the movement of particles is impeded, which causes the device to enhance the V_OC. In Fig. 4d, it’s demonstrated that the PCE of the PSCs peaks at a doping of 1 × 10¹⁷ cm⁻³ for CsGeI₃ and 1 × 10¹⁶ for CsSnGeI₃ perovskite materials, attaining a PCE of approximately 34.18% at a thickness of 800 nm for both PALs. As doping rises, the output parameters of the PSC increase except J_SC. Nonetheless, the V_OC attains its peak value of 1.25 V at a doping density of 1 × 10¹⁷ cm⁻³ for CsGeI₃ and 1 × 10¹⁶ for CsSnGeI₃ perovskite materials (Fig. 4c). The J_SC shows a continuous reduction with rising doping of CsSnGeI₃. At an optimized doping for both PALs, the highest J_SC attains 32.67 mA/cm² (Fig. 4a). Furthermore, the FF accomplishes 83.64% at this adjusted doping concentration (Fig. 4b).
Figure 5a–d illustrates the alteration in defect density (DD) in the PAL, ranging from 1 × 10¹⁰ to 1 × 10¹⁶ cm⁻³. We found that DD extensively influences the output parameters, as shown in Fig. 5a–d. The analysis focuses on CsGeI3 and CsSnGeI₃ absorber layers. Output parameters demonstrate a decrease with increasing DD in the active layer except for FF, suggesting a relationship between trapping of carrier and DD inside the solar cell. An increase in DD enhances recombination of carrier by capturing electrons and holes, which results in loss of energy as they interact inside the crystal lattice, thus promoting recombination owing to lower levels of carrier energy ^56,57. As trap density rises, the increased recombination process results in a deterioration of PSC performance⁵⁸, which could potentially lead to device overheating. Therefore, it is essential to keep defect density in tolerable limits, around 10¹² cm⁻³, considering the permissible current and voltage thresholds of the CsGeI₃​ layer (1.363 eV) and CsSnGeI₃​ layer (1.5 eV). Figure 5d illustrates that the PCE becomes the highest at a DD of 1 × 10¹² cm⁻³ for individual perovskite materials, attaining approximately 34.18% for the thickness of 800 nm of both PALs. As DD upsurges, the performance parameters of the PSC decline except FF. However, V_OC reaches its peak value 1.25 V at a defect density of 1 × 10¹² cm⁻³ for both perovskite materials (Fig. 5c). J_SC shows a nonstop reduction with rising defect density, continuously deteriorating the output. At an adjusted DD of 1 × 10¹² cm⁻³ for both PALs, the maximum J_SC becomes 32.67 mA/cm² (Fig. 5a). In addition, FF achieves 83.64% at this optimized DD (Fig. 5b).
Impact of absorber defect density on performance parameters of PSCs: a J_SC, b FF, c V_OC, d PCE.
Temperature poses a considerable challenge to the performance of PSCs, as shown in Fig. 6, where the PV parameters of the PSC are examined across a temperature range of 300 to 420 K. The analysis shows that when the temperature rises, the J_SC tends to rise, whereas the FF, V_OC, and PCE decline. This phenomenon specifies that higher temperatures promote thermal mobility of electrons and holes in the PSC, possibly contributing to increased J_SC. Nevertheless, elevated temperatures can cause the absorber layer to behave like an ohmic conductor, thereby obstructing the movement of the carrier and converting electrical energy into heat, which consequently lowers output parameters⁵⁹. Inadequate dissipation of temperature within various parts of the PSC can intensify the increase in temperature, risking damage to the PSC. Consequently, it is vital to wisely evaluate the performance limits of every active layer when fabricating heterojunction solar cells. The J_SC remains nearly unchanged across the temperature range, as the photon absorption and carrier generation processes in the absorber layers are largely unaffected by thermal variations⁶⁰. Similarly, the V_OC shrinkages from 1.25 V at 300 K to 1.20 V at 420 K. In parallel, the FF experiences a notable reduction, dropping from 83.64% at 300 K to 79.91% at 420 K. The efficiency exhibits the maximum value of 34.18% at lesser temperatures, lessening to 31.71% as temperature boosts (Fig. 6(a)).
The influence of temperature on a photovoltaic output and b the J–V characteristics of the PSC at various temperatures employing a double PAL configuration.
Furthermore, the optimized PSC exhibits a more pronounced temperature gradient, showing an average reduction of -0.0265%/K in efficiency. Figure 6b also illustrates the J–V characteristics under different temperature, specifically emphasizing the significance of temperature’s impact. Temperature influences material characteristics such as charge carrier mobility and density, leading to diminished cell performance⁶¹. Table 3 presents the maximum parameters achieved under optimized temperature conditions.
The results stated in “Exploration of the band structure characteristics of PSCs” to “Impact of temperature on the output of PSCs” have assumed an appropriate interface in the current heterojunction, where the defect density and related interfacial recombination remained undetermined. To analyze the impact of interfacial (IF) defect density is crucial for solar cells, as these defects significantly affect performance by promoting carrier recombination, ultimately reducing the PCE of PSCs. Recognizing the relationship between IF defect density and output has driven researchers to devise strategies to minimize defect formation and enhance PSC efficiency. The impact of IF defect on PSCs contributes to a clear understanding of solar cell physics, opening the door for innovative materials and advanced deposition techniques. Further simulations were conducted to assess the effect of the Cu₂O/CsGeI₃, CsGeI₃/CsSnGeI₃ and CsSnGeI₃/SnS₂ IF on SC photovoltaic (PV) outputs. The IF defect density ranged from 1 × 10¹⁰ cm⁻² to 1 × 10¹⁶ cm⁻², and the respective device performance was evaluated. For the interface of Cu₂O/CsGeI₃ in Fig. 7a, increasing IF density led to a negligible impact on J_SC but significantly lowered V_OC from 1.25 volts to 1.17 volts, whereas FF is rising from 83.6% to 88% due to defect-induced band bending at the interface, which can enhance built-in electric fields and improve charge carrier separation and extraction under certain conditions. IF defects can generate recombination centers, reducing carrier transport efficiency in the PSC and resulting in decreased V_OC and FF, ultimately lowering PCE¹⁴ from 34.18% to 32.68%. At the CsGeI₃/CsSnGeI₃ interface in Fig. 7b, higher IF density had maximal effect on the J_SC which decreasing from 32.67 mA/cm² to 24.62 mA/cm² and V_OC reduces from 1.25 to 0.94 volts, accompanied by a decrease in the FF from 88.64 to 76.02% and lowering the PCE from 34.18 to 17.76%. Similar trends were observed for CsSnGeI₃/SnS₂ interface Fig. 7c, where increasing IF density led to reduced PCE but J_SC remained constant.
The influence of interface DD on the photovoltaic output of the PSC; a Cu₂O/CsGeI₃, b CsGeI₃/CsSnGeI₃, and c CsSnGeI₃/SnS₂, respectively.
Figure 8 demonstrates the influence of series resistance (R_S) on the performance of the optimized PSC that utilizing a double-graded absorber layer. The results indicate that the most favorable outcomes are achieved at 0 Ω.m resistance which represents the optimal series resistance. However, increasing series resistance exhibits a constant trend in both J_SC and V_OC. Enhancing series resistance in a solar cell leads to higher voltage drops, greater power dissipation, and a lower maximum power point. These factors collectively reduce the FF continuously resulting a continuous decline in PCE from 34.18% to 28.5%.
The influence of series resistance on the outputs of the optimized PSC.
Figure 9a, examines the J–V properties for both the single PAL (CsGeI₃ and CsSnGeI₃) and the double PALs (CsGeI₃/CsSnGeI₃)-based solar cell architecture under improved conditions. The simulated results reveal that the dual PAL demonstrates a superior J_SC value due to its ability to absorb photons in the broader energy range, thereby increasing exciton generation. In comparison, the dual PALs yield a J_SC of 32.67 mA/cm², while the single PAL CsGe3I₃ achieves a J_SC of 32.42 mA/cm² and for CsSnGeI₃ the J_SC is 27.30 mA/cm². Additionally, the solar cell with the double PALs exhibits a lower V_OC compared to CsSnGeI₃-based PSC, attributed to higher recombination rates within the dual PAL. Specifically, the CsGeI₃/CsSnGeI₃ double PALs offer a V_OC of 1.25 volts, whereas the single PAL CsSnGeI₃ achieves a V_OC of 1.30 volts.
Figure 9b, illustrates the optimized quantum efficiency (QE) spectrum for dual and single active layers. The QE values are lower relative to the dual PAL of CsGeI₃/CsSnGeI₃ due to the broader absorption spectrum of dual PALs, which absorb a wider portion of light wavelengths encompassing low as well as high bandgaps⁶². The QE curve for dual absorber indicates that throughout the full depth of the active layer (800 nm), the QE have a tendency to saturate, reaching its peak efficiency. Nonetheless, it quickly diminishes to zero at the cutoff wavelength of 1050 nm. After sensibly taking into account the balance among PV parameter values, 800 nm was identified as the optimal thickness. These findings regarding J–V attributes are assisted by the QE spectra. For further assessment, the optimum simulated performance for the final solar cells is summarized in Table 3 which revealed better performance compared to other designs.
The a J–V characteristics, and b QE spectra of single, and double PSCs.
As shown in Table 3, the proposed CsSnGeI₃/CsGeI₃-based PSC with optimized parameters achieves a superior PCE of 34.18%, which is significantly higher than the values reported for other dual absorber designs in previous studies. This improvement can be attributed to the broader spectral absorption, better energy level alignment, and improved carrier separation facilitated by the carefully engineered heterojunction structure. The comparison highlights the effectiveness of our material selection and optimization strategy in surpassing the performance of earlier reported lead-free and dual absorber solar cell configurations.
This research demonstrates the potential of dual absorber layer designs in hybrid-PSCs to enhance photovoltaic performance. By employing a CsSnGeI₃/CsGeI₃ heterojunction, we achieved an extensively rise in PCE, reaching up to 34.18% under optimal conditions with CsGeI₃ and CsSnGeI₃ thicknesses around 800 nm, doping levels at approximately 1 × 10¹⁷ cm⁻³ for CsGeI₃ and 1 × 10¹⁶ for CsSnGeI₃, and suggested defect density at around 1 × 10¹² cm⁻³ for both absorbers. These metrics represent a substantial improvement over single absorber layer designs, highlighting the effectiveness of the double absorber approach. The enhanced efficiency is primarily results from the broader absorption spectrum and improved charge carrier separation facilitated by the heterojunction. Our simulation-based analysis underscores the importance of optimizing absorber layer thickness, doping concentrations, and defect densities to maximize device output. Additionally, the study highlights the critical role of maintaining appropriate rear contact electrode temperatures, and minimizing series resistances. This dual absorber layer design using CsSnGeI₃/CsGeI3₃ heterojunctions offers a promising pathway to meaningfully advance the efficiency of PSCs to develop more effective and stable PSCs.
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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A. Irfan extends his appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work through the Large Groups Research Project under grant number (RGP2/71/46).
Advanced Energy Materials and Solar Cell Research Laboratory, Department of Electrical and Electronic Engineering, Begum Rokeya University, Rangpur, 5400, Bangladesh
Md. Ferdous Rahman, Mahabur Rahman & Md. Rezwanul Islam
Department of Physics, Rajshahi University of Engineering and Technology, Rajshahi, 6204, Bangladesh
Md. Faruk Hossain
Department of Physics, Astronomy Texas A&M University-Commerce, 2200 Campbell St, Commerce, TX, 75429, USA
Sahjahan Islam & Dipika Das Ria
OTEA, Department of Engineering Sciences, Faculty of Sciences and Techniques, Moulay Ismail University of Meknes, Boutalamine, BP 509, 52000, Errachidia, Morocco
Abdellah Benami
Department of Chemistry, College of Science, King Khalid University, P.O. Box 9004, 61413, Abha, Saudi Arabia
Ahmad Irfan
Department of Physics, Faculty of Science, University of Tabuk, 71491, Tabuk, Saudi Arabia
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Rahman, M.F., Rahman, M., Hossain, M.F. et al. Unraveling high-efficiency lead-free perovskite solar cells using a CsSnGeI₃/CsGeI₃ dual absorber and a Cu₂O HTL. Sci Rep 15, 42865 (2025). https://doi.org/10.1038/s41598-025-26935-9
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Received: 30 March 2025
Accepted: 31 October 2025
Published: 01 December 2025
Version of record: 01 December 2025
DOI: https://doi.org/10.1038/s41598-025-26935-9
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