Simulation of optimum band structure of HTM-free perovskite solar cells based on ZnO electron transporting layer

Expensive gold electrode and hole transporting material (HTM) currently used in perovskite solar cells are the major economic constraints to the scaling-up of this promising technology. Designing high-efficiency perovskite solar cell with graded band-gap structure to replace HTM and with low-cost electrode is urgently needed for real cell production. In our work numerical simulation of perovskite solar cell with the configuration of FTO/ZnO/CH3NH3Pb(I1-xBrx)3/Carbon is performed using SCAPS-1D program. The band gap of CH3NH3Pb(I1-xBrx)3 absorber is tuned in the range of 1.5 eV to 2.3 eV by variation of the Br doping content. Both the uniform band gap and graded band gap absorber were examined. Based upon the simulated results, a promising efficiency of 17.89% can be realized with a back grading profile that consists of a graded thickness of 50 nm as well as 1.9 eV band gap at back surface. This work will provide guidelines for further efficiency enhancement of low cost perovskite solar cells.