Numerical simulation of charge transport layer free perovskite solar cell using metal work function shifted contacts

Perovskite solar cells (PSCs) are one of the fastest emerging photovoltaic (PV) technology at the research level. To achieve higher conversion efficiencies from PSCs, a perovskite absorber layer is stacked between two charge transport layers (CTLs) such as electron and hole transport layers. However, fabrication of defect-free multi-layered PSC is a challenging task, and the presence of CTL and their corresponding interfaces with perovskite enhances the recombination, hysteresis and led to poor stability. Here, in this work, CTL free (i.e., electron and hole transport layer free) PSC is simulated using metal work function shifted contacts. The device presented in this work is free from transport layers and the collection process is with the help of an electric field across the perovskite layer. The electric field is created by using two metals of different work function, i.e., 4.35 eV and 5.25 eV (can be realized using self-assembled monolayers technique) used as cathode and anode respectively. Simulated CTL free PSC exhibits J(sc) = 17.8 mA cm(-2), V-oc = 712 mV, FF = 68.5% and PCE = 8.7% with 250 nm thick perovskite absorber layer having bulk defect density of 2.5 x 10(13) cm(-3) . Further, a comprehensive study is done in terms of front electrode work function (FEW), front electrode transparency, perovskite thickness and bulk defect density to understand the impact of these parameters on the performance of the device. To understand the behavior of the device, the energy band diagram profile is examined. Reported results show that higher metal work function difference between front and back electrode, higher transparency, and thick perovskite layer with low defect density results in better PV effect in CTL free PSC. Optimized CTL free PSC device delivers J(sc) = 19.9 mA cm(-2) , V-oc = 726 mV, FF = 66.8% and PCE = 9.7%. The design simulated in this work opens up a new window for next-generation interface defect and hysteresis-free PSC.