Analytical Solutions for Current–Voltage Properties of PSCs and Equivalent Circuit Approximation

Perovksite solar cells have emerged as a promising photovoltaic technology due to their high increasing power conversion efficiency (PCE). However, challenges related to thermal instability and material toxicity, especially in lead-based perovskites, bring the need to investigate alternative materials and structural designs. This study investigated the current–voltage and power–voltage characteristics of lead-free PSCs based on tin- and germanium using a two-diode equivalent circuit model. The novelty of this work was based on the intensive evaluation of three different electron transport layers (ETLs)—titanium dioxide (TiO2), zinc oxide (ZnO), and tungsten trioxide (WO3)—under different ambient temperature conditions (5 °C, 25 °C, and 55 °C) to study their impacts on device performance and the thermal stability. SCAPS-1D simulations were used to model the electrical and optical behaviors of the proposed perovskite structures, and the results were validated by using the two-diode model. The main performance parameters that were considered were open-circuit voltage, short-circuit current, maximum power point, and fill factor. The results showed that TiO2 was better than ZnO and WO3 as an ETL, achieving a PCE of 24.83% for Sn-based perovskites, and ZnO was the better choice for Ge-based perovskites at 25 °C, with an efficiency reaching ~15.39%. The three ETL materials showed high thermal stability when analyzing them at high ambient temperatures reaching 55 °C.