Impact of grain boundary defect on performance of perovskite solar cell

Methyl ammonium lead halide (MAPbI₃) perovskite is a crystalline material. It shows interesting properties that are suitable for absorber layer of solar cell. An optimized solar cell requires 200–400 nm thick absorber layer. However, the thin absorber layer inevitably contains grain of crystallites and hence grain boundary (GB) defects. The GB defects affect device performance. Therefore, we theoretically investigated the effects of GB defects on performance of solar cells. In this simulation studies, we kept total mid-gap defect density (N_d) as constant at 4×10¹⁷ cm⁻³ but varied the GB defect density (GB_dd) from 3×10¹² cm⁻³ to 3×10²² cm⁻³, because of which, the observed short circuit current density (J_sc) of the cells remain nearly unchanged, but the open circuit voltage (V_oc) and power conversion efficiency (PCE) decreased steadily, while the fill factor (FF) shows a different trend of variation in a region (Region-X, say) where the GB_dd and the N_d were nearly equal. A further investigation reveals that in the Region-X, a transition happens from defect mediated recombination to GB mediated recombination, where the reverse saturation current density (J₀) and diode ideality factor (n) of the solar cells, reduce sharply from 3.46×10^–13 A cm⁻² to 2.65×10^–19 A cm⁻² and 1.9 to 1.1, respectively for a cell with 200 nm thick absorber layer. For 400 nm thick absorber layer, reduction of these parameters was 1.96×10^–13 A cm⁻² to 1.20×10^–17 A cm⁻² and 1.8 to 1.2 respectively.