Despite significant advances in lead-free perovskite photovoltaics, achieving a balance among environmental safety and high optoelectronic performance remains challenging. The inorganic double perovskite Cs2AgBiBr6 has emerged as a promising candidate owing to its robust three-dimensional crystal structure and suitable visible-range bandgap. However, best power conversion efficiencies (PCEs) for Cs2AgBiBr6 solar cells reported so far - 6.37% experimentally and 27.78% in numerical studies - remain below the theoretical performance potential, largely due to suboptimal charge transport layers, and interface-related recombination losses. Here, we address this gap using a 3D finite-element method (FEM) implemented in COMSOL Multiphysics, which couples optical simulations with semiconductor drift-diffusion transport. To our knowledge, this work represents the first comprehensive 3D FEM-based study of a double halide perovskite solar cell. Screening of 25 electron transport layer (ETL)-hole transport layer (HTL) combinations identifies CeO2 and P3HT as the optimal ETL and HTL respectively. Device performance is further analyzed through systematic variation of layer thicknesses, doping concentrations and defect densities within the FTO/CeO2/Cs2AgBiBr6/P3HT/Au architecture. Under optimized parameters, the simulated device achieves a PCE of 31.76%, representing the theoretical upper bound predicted by the model. Overall, this work demonstrates 3D physics-based device engineering as a decisive pathway for overcoming efficiency bottlenecks in lead-free double perovskite photovoltaics.
Deep Dive into Three-Dimensional Optical-Electrical Simulation of Cs2AgBiBr6 Double Perovskite Solar Cells.
Despite significant advances in lead-free perovskite photovoltaics, achieving a balance among environmental safety and high optoelectronic performance remains challenging. The inorganic double perovskite Cs2AgBiBr6 has emerged as a promising candidate owing to its robust three-dimensional crystal structure and suitable visible-range bandgap. However, best power conversion efficiencies (PCEs) for Cs2AgBiBr6 solar cells reported so far - 6.37% experimentally and 27.78% in numerical studies - remain below the theoretical performance potential, largely due to suboptimal charge transport layers, and interface-related recombination losses. Here, we address this gap using a 3D finite-element method (FEM) implemented in COMSOL Multiphysics, which couples optical simulations with semiconductor drift-diffusion transport. To our knowledge, this work represents the first comprehensive 3D FEM-based study of a double halide perovskite solar cell. Screening of 25 electron transport layer (ETL)-hole t
The urgent need to mitigate climate change and reduce dependence on fossil fuel-based power generation has accelerated the global transition toward clean and renewable energy technologies [1], [2]. Among the available renewable resources, solar energy is the most abundant and universally accessible, making photovoltaic (PV) conversion a central pillar of future sustainable energy systems [3]. While crystalline silicon solar cells continue to dominate the commercial market due to their technological maturity, their energy-intensive manufacturing and high processing temperatures motivate continued exploration of alternative absorber materials capable of delivering high efficiency through scalable, low-temperature fabrication routes [4] [5]. Third-generation photovoltaic technologies-including dye-sensitized, organic, quantum dot, and perovskite solar cells-have therefore attracted extensive research interest [6]. In particular, lead (Pb)-based hybrid organicinorganic halide perovskites have achieved a remarkable rise in power conversion efficiency (PCE), from 3.8% in 2009 [7] to 26.95% in 2025 [8], approaching crystalline silicon benchmarks. These materials typically adopt the ABX3 perovskite structure (Fig. 1a), where A denotes a larger organic or inorganic cation (CH3NH3 + , CH(NH2)2 + , Cs + , K + , Na + etc.), B corresponds to a divalent metal cation─most commonly Pb 2+ ─and X represents a halide anion (I -, Br -, or Cl -). This crystal model enables compositional tunability while supporting the outstanding optoelectronic properties of perovskite absorbers, including strong optical absorption, long carrier diffusion lengths, low exciton binding energies, and balanced charge transport [9]. However, despite these exceptional properties, large-scale deployment remains constrained by Pb toxicity and long-term instability associated with Among the reported HDPs, Cs2AgBiBr6 ─ crystallizing in the cubic elpasolite-type double perovskite structure (space group Fm3̅ m) ─ has attracted particular attention as a benchmark inorganic lead-free perovskite absorber [11], [26]. The cooperative incorporation of Ag + and Bi 3+ at the B′ and B″-sites enhances lattice stability, resulting in a high decomposition energy and exceptional resistance to thermal and moisture-induced degradation [27]. In addition to its robust structural stability, Cs2AgBiBr6 exhibits a suitable visible-range bandgap, long radiative and nonradiative carrier lifetimes, relatively low carrier effective masses, and notable defect tolerance-properties that are essential for efficient photovoltaic operation [10], [22], [28]. Importantly, several of these optoelectronic characteristics approach those of archetypal Pb-based perovskites, while offering the decisive advantages of low toxicity and long-term environmental compatibility [29]- [31].
Since its initial incorporation into photovoltaic devices by Greul et al. [32] using a planar FTO/TiO2/Cs2AgBiBr6/Spiro-OMeTAD/Au architecture, which delivered a PCE of 2.43% and established the experimental feasibility of this absorber, Cs2AgBiBr6 has been explored extensively across diverse device architectures, contact layer combinations, and deposition routes, including both solution-processed and vapor-deposited films [33], [34]. Continuous experimental progress has led to the current record efficiency of 6.37%, achieved by Zhang et al. via optimized planar architectures (ITO/SnO2/Cs2AgBiBr6/Spiro-OMeTAD/Au), demonstrating excellent operational stability (1440h at 85°C) as well [28]; however, the performance remains modest relative to Pb-based counterparts. In parallel, numerical studies suggest that significantly higher efficiencies may be achievable through appropriate selection of charge transport layers and careful optimization of material and interfacial parameters [35]- [38]. For instance, Danladi et al. reported a PCE of 25.56% for the FTO/ZnO/Cs2AgBiBr6/CFTS/Au structure [36]. Hakami et al. proposed an all-inorganic device architecture based on FTO/TiO2/Cs2AgBiBr6/NiO/Au, achieving a simulated PCE of 26.71% [37]. Similarly, Srivastava et al. identified an optimized planar FTO/AZO/Cs2AgBiBr6/ZnTe configuration, predicting a PCE of 26.89% [35]. More recently, Raj et al. reported an optimized efficiency of 27.78% for the FTO/TiO2/Cs2AgBiBr6/Cu2O/Au structure [38]. Collectively, these insights motivate a systematic device-level optimization strategy in which suitable electron transport layer (ETL)-hole transport layer (HTL) combinations are first identified, followed by targeted tuning of layer thicknesses, doping concentrations, and bulk and interfacial defect densities, with the aim of identifying realistic pathways toward performance enhancement in Cs2AgBiBr6-based solar cells. Despite the advances, most prior modeling efforts rely on one-dimensional drift-diffusion solvers that assume simplified generation profiles and neglect spatial optical redistribution and multidimensional interfacial effects. The
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