Highly efficient, low-cost, lead-free bifacial perovskite solar cells: A designing strategy through simulation

The bipolar properties of perovskites make it fascinating to design a perovskite solar cell (PSC) without a hole transport layer (HTL). An HTL-free PSCs provide easy fabrication, are low-cost, and time-saving. In HTL-free PSCs, the crystallinity and morphology of perovskite film can enhance device performance. With the bifacial approach, the device efficiency can be further enhanced. In the present work, HTL-free bifacial PSCs have been simulated, and a strategy has been provided to design a high-performance device. In investigating the effect of various electron transport layers (ETLs) and lead-free perovskite layers, we observed that a suitable combination of ETL and perovskite is vital to achieve a higher power conversion efficiency (PCE). The Mott-Schottky analysis of ETL/perovskite interfaces reveals that the built-in potential depends on the bandgap of the perovskite absorber layer, which affects the device performance by setting up higher open circuit voltage (VOC). A higher dielectric material between the ETL and the perovskite layer improves the device performance. Additionally, lowering the doping density of the perovskite layer increases the bifacial factor of the device. While optimizing our cells, the champion device with configuration FTO/Zn2SnO4/MASnI3/UT-Au (ultra-thin gold) exhibits a PCE of 19.76 % and 15.97 % for the front and rear illumination, respectively. By replacing UT-Au with MAM(MoOx/Ag/MoOx) transparent conducting triple-layer electrode, our device shows an improved PCE of >25 % for both front and rear illumination. The outcomes of these studies are anticipated to be beneficial in designing and optimizing HTL-free bifacial PSCs in the experiment.