Study the effect of band offsets on the performance of lead-free double perovskite solar cell

Abstract

The present study investigates the effect of band offsets engineering for lead–free (Pb-free) all-inorganic double-perovskite solar cell (DPSC) using the solar cell capacitance simulator one dimensional (SCAPS 1D). The initial simulation study is carried out by using Cs2AgBi0.75Sb0.25Br6 based double-perovskite layer along with 2,2′,7,7′-tetrakis[N,N-di4-methoxyphenylamino]-9,9′-spirobifluorene (SpiroOMeTAD) as a hole transport layer (HTL) and zinc oxide (ZnO) as an electron transport layer (ETL) which shows the device efficiency of 11.35%. Further, the impact of the conduction band offset (CBO) and valence band offset (VBO) is studied to improve the device performance. The proposed study suggests that extremely negative and positive CBO resulted in limited PV performance. This is mainly due to the reason that in extremely negative CBO limits the Vbi and thus VOC. However, the extreme positive CBO leads to the formation of a barrier spike which restricts the device performance. Similarly, the positive VBO leads to band misalignment which further deteriorates the device performance. Hence, it has been revealed from the numerical simulation, that the optimum conduction band offset (CBO) is found to be −0.1 eV to +0.1 eV and the optimum valence band offset (VBO) is found to be −0.1 eV–0.00 eV with respect to the double-perovskite absorber layer. It has been found that with the introduction of copper (I) thiocyanate (CuSCN) as a hole transport layer (HTL) and zinc oxysulfide (ZnOS) as an ETL the overall power conversion efficiency (PCE) improves up to 18.26% which is an outstanding improvement in the lead-free double–perovskite solar cell. In addition, the effect of the thickness of the perovskite layer is also studied in which the optimized double-perovskite layer thickness obtained is 400 nm. Thus, the proposed simulation study provides significant insight for the researchers that will help to find out the suitable ETL and HTL for Pb-free DPSC.