Design and Simulation of Electron and Hole Transport Layer for Lead Free Perovskite Solar Cell Application

Abstract

The perovskite solar cells are an emerging photovoltaic technology as it reaches 25.5% efficiency within a decade. Due to this rapid advancement researchers have developed various perovskite absorber layers, charge transport layers, transparent conducting oxides and metal contacts. However, it is quite complicated to fabricate numerous combinations of these layers and hence the simulation is an efficient way to analyse the best possible combination which can result in higher device performance. In the present thesis work, the numerical simulation of lead-free perovskite solar cells is performed using SCAPS 1D software. The current study brings forth the numerical simulation of various lead-free perovskite alternatives having narrow and wide bandgap configurations. For the narrow bandgap configuration, the FA0.75MA0.25Sn0.25 Ge0.5I3 and CsSnGeI3 based perovskite layers are considered. However, for the wide bandgap application, the CH3NH3GeI3 based perovskite layer is considered. The perovskite solar cells using these layers are optimized based on charge transport layers, perovskite absorber layer thickness, perovskite absorber defect density and their energy band alignment with respect to the contacts. To investigate the effect of charge transport layers (i.e., hole transport layer and electron transport layer), the work shows that the correlation of VOC with the built-in potential (Vbi). The results disclosed that to attain better VOC and PV performance, the device should exhibit the better Vbi and proper band alignment that allows the efficient facilitation of charge carriers, along with good charge carrier mobility. Thus, it is suggested that for the proper transport of electrons, the conduction band minimum of the electron transport layer (ETL) must lie below the conduction band minimum of the perovskite layer. Similarly, in the case of hole transport, the valence band maximum of the hole transport layer must lie above that of the perovskite layer.