Investigation of Sr-doped ZnO electron transport layers for perovskite solar cells: a combined DFT and SCAPS-1D study

Abstract

This study investigates strontium (Sr)-doped zinc oxide (ZnO) as an electron transport layer (ETL) for lead-free perovskite solar cells (PSCs) through a combined density functional theory (DFT) and SCAPS-1D simulation approach. The opto-electronics properties of pristine and Sr-doped ZnO were analysed using the mGGA functional implemented in CASTEP. The results revealed that Sr doping tunes the electronic structures of ZnO by reducing the band gap from 3.37 eV to 2.91 eV, while improving carrier mobility and optical absorption. Density of states (DOS) analysis confirmed that Sr doping enhances electron extraction capability. Optical investigations demonstrated high transparency in the visible region and tunable absorption behaviour suitable for photovoltaic applications. Device simulations were performed for a FTO/Sr–ZnO/FASnI3/spiro-OMeTAD/Au structure using SCAPS-1D. Optimization studies indicated that an ETL thickness of 150 nm and donor density of 1 × 1020 cm−3 provided the best performance, achieving an efficiency of 16.08% for the proposed PSCs. The study demonstrated that interface defect density, band alignment, series resistance, temperature, and back-contact work function strongly influence device performance. Overall, Sr-doped ZnO exhibits promising characteristics as an efficient ETL for stable and high-performance lead-free PSCs.