A Novel Perovskite Solar Cell Comprising CsPbI2Br/Cs2SnI6 (CsGeI3) Cascade Absorbing Bilayer and Cr2O3 Electron Transport Material: A Theoretical Comparison Study

In order to prevent the limitation on absorbing energies by a single-layer perovskite solar cells (PSCs), a cell comprising bilayer heterostructure in the form of FTO/Cr2O3/CsPbI2Br +Cs2SnI6 (CsGeI3)/spiro-OMeTAD/Au is simulated and its photovoltaic performance including incident photon-to-current conversion efficiency, fill factor, open circuit voltage and short circuit current is evaluated using SCAPS 1D software package. It is shown by introducing these structures, not only a wider range of the sunlight spectrum is exploited, but also by achieving a favorable band-edge bending as graded band gap, more charge carriers can be collected. Moreover, further improvement in the performance of devices is obtained by optimizing the thickness of absorbing layers and work function of the back electrode. The thermal stability of PSCs is investigated by varying the temperature in the range of 300-480K and the effect of various electron transport materials (ETMs) on the performance of the cell is evaluated. Under optimized condition, it is found that the efficiencies of the cells with CsPbI2Br+Cs2SnI6 and CsPbI2Br+CsGeI3 bilayer heterostructures increase from 13.38% for non-heterojunction structure to 15.14% and 16.34%, respectively. Furthermore, the simulation results reveal that the photovoltaic cell made of CsPbI2Br+CsGeI3 absorbing layer having higher efficiency and greater thermal stability (compared to PSC made of CsPbI2Br+Cs2SnI6 absorbing layer) is an appropriate and promising candidate as efficient perovskite solar cell.