Performance enhancement of HTL free perovskite solar cells through ETL and back contact engineering

Abstract Research on perovskite solar cells (PSCs) has surged due to their promising power conversion efficiency and low fabrication costs. However, the commercial viability of PSCs is hindered by the complex synthesis of the conventional hole transport layer (HTL), such as Spiro-OMeTAD, and the limitations of gold (Au), which is commonly used as a back contact. Specifically, Au tends to diffuse into the perovskite layer over time and react with halide ions, leading to device degradation and reduced long-term stability. In this study, a comprehensive simulation is conducted to evaluate the performance of PSCs with and without HTL, incorporating various metal back contacts. The impact of metal work functions on device performance is systematically investigated. Among the metals analysed, platinum (Pt) emerged as the optimal contact for both configurations due to its high work function and ability to form a stable interface. Focusing on HTL-free designs for structural simplicity, the study explored alternative electron transport layers (ETLs) to replace conventional titanium dioxide (TiO₂), which suffers from poor optoelectronic properties and ultraviolet instability. The performance of various inorganic ETLs, including CdZnS, WS₂, WO₃, ZnO, ZnOS, and ZnSe, is evaluated using SCAPS-1D simulation tool in a typical perovskite solar cell architecture. Among them, ZnOS emerged as the most promising ETL with an open-circuit voltage ( V oc ) of 1.22 V, a short-circuit current density ( J sc ) of 27.62 mA/cm 2 , a fill factor (FF) of 83.86%, and a power conversion efficiency of 28.39% under optimised conditions. Additionally, an interface defect layer (IDL) of BiI₃ (Bismuth triiodide) is introduced to enhance the long-term device stability. With the IDL, the structure exhibits V oc of 1.13 V, J sc of 28.88 mA/cm 2 , FF of 88.48%, and a power conversion efficiency of 28.78%. These findings highlight the potential of Pt-based, HTL-free PSCs for efficient and stable photovoltaic applications.