Achieving 27.20% efficiency for a lead-free double perovskite solar cell with all inorganic Cs2BiAgI6 using AZO UTL as a passivation layer†

Abstract

A major challenge in the commercialization of perovskite solar cells (PSCs) is the presence of toxic metals, like lead, in their composition. Compared with conventional lead halide perovskites, double halide perovskites have garnered significant interest owing to their reduced toxicity, adjustable bandgap, structural flexibility, and enhanced stability. This study focuses on evaluating a lead-free Cs₂BiAgI₆-double perovskite solar cell (DPSC) using a one-dimensional solar cell capacitance simulator (SCAPS-1D) with a bilayer ZnO/AZO electron transport layer (ETL) and ZnO ETL, along with various hole transport layers (HTLs) for the first time. The selected HTLs included CBTS, Cu₂O, CuAlO₂, CZTS, CuSCN, spiro-OMeTAD, MoO₃, and V₂O₅. Various factors, such as energy band alignment, recombination and generation rates, absorber thickness, defect and doping densities for all layers, energy levels of ETLs and HTL, interfacial defect densities, back metal contact, and operating temperature, were examined for improving the performance of DPSC. This study was aimed at enhancing the efficiency and deepening our understanding of the electron transport mechanisms in Cs₂BiAgI₆-DPSCs. The research findings suggested that V₂O₅ and ZnO/AZO were the most suitable materials for the HTL and ETL, respectively, among the various options considered. Therefore, we utilized ITO/ZnO/AZO/Cs₂BiAgI₆/V₂O₅/Au as the required DPSC. To boost the performance of the DPSC, electron–hole pair handling at the ETL/perovskite interface was optimized by adding a 10 nm AZO UTL, thereby enhancing the ZnO/double perovskite interface properties. The bilayer structure of ZnO/AZO offered advantages such as efficient electron extraction and minimal interfacial recombination owing to its enhanced energy level alignment and defect passivation. After optimizing these parameters, the system with the ZnO/AZO bilayer ETL achieved an efficiency of 27.20%, along with a V_oc of 1.3221 V, J_sc of 23.84 mA cm⁻², and FF of 86.28%. Thus, this work presents a straightforward and promising approach for fabricating photovoltaic devices, particularly for various types of double perovskites, with favorable charge transport layers and recombination properties. Furthermore, these findings offer theoretical guidance to improve the efficiency of Cs₂BiAgI₆-based photovoltaic solar cells (DPSCs) and facilitate the widespread adoption of eco-friendly and stable perovskites.