Physical parameter optimization and band alignment approach for efficiency improvement in Cs2AgBiBr6 based lead-free perovskite solar cells

In recent years, organic-inorganic halide perovskite solar cells (PSCs) have garnered significant global attention due to their exceptional performance and high-power conversion efficiency (PCE). The impressive device capabilities have encouraged extensive research into various advanced engineering strategies aimed at improving the physical characteristics of PSCs. Nevertheless, while lead-based PSCs have achieved outstanding PCEs, concerns regarding lead toxicity and long-term stability hinder their commercial viability. Besides, an appropriate hole transport material is also required to reduce the recombination losses at interfaces. In the present study, PSCs were designed in SCAPS simulation software with cell configuration of FTO/TiO₂/Cs₂AgBiBr₆/HTLs (CuI, CuSCN, Cu₂O, Spiro-OMeTAD)/Au. Here, lead-free stable double perovskite material Cs₂AgBiBr₆ is used as light absorbing material and TiO₂ electron transport material. However, device response of PSCs is studied with different hole transport materials. With optimization of defects, and thickness of perovskite absorber, along with operating temperature and series resistance, Cu₂O as hole transport layer (HTL) based PSCs have achieved open-circuit voltage (V_OC) of 1.33 V, current density of (J_SC) of 8.78 mA/cm², fill factor (FF) of 64.96%, and PCE of 7.60%. The reason behind the variation in device performance was realised using capacitance-voltage (C-V), conductance-voltage (G-V), capacitance - frequency (C-f) and, conductance-frequency (G-f) analysis. It has been found that Cu₂O HTL-based PSCs exhibited reduced defects at the interfacial region, attributed to the appropriate band alignment with the Cs₂AgBiBr₆ perovskite absorber. The suggested simulation study may contribute significantly to the advancement of lead-free all-inorganic PSCs, aiming for improved efficiency.