The Interplay between Trap Density and Hysteresis in Planar Heterojunction Perovskite Solar Cells

Anomalous current-voltage (J-V) hysteresis in perovskite (PSK) solar cell is open to dispute, where hysteresis is argued to be due to electrode polarization, dipolar polarization, and/or native defects. However, a correlation between those factors and J-V hysteresis is hard to be directly evaluated because they usually coexist and are significantly varied depending on morphology and crystallinity of the PSK layer, selective contacts, and device architecture. In this study, without changing morphology and crystallinity of PSK layer in a planar heterojunction structure employing FA_0.9Cs_0.1PbI₃, a correlation between J-V hysteresis and trap density is directly evaluated by means of thermally induced PbI₂ regulating trap density. Increase in thermal annealing time at a given temperature of 150 °C induces growth of PbI₂ on the PSK grain surface, which results in significant reduction of nonradiative recombination. Hysteresis index is reduced from 0.384 to 0.146 as the annealing time is increased from 5 to 100 min due to decrease in the amplitude of trap-mediated recombination. Reduction of hysteresis by minimizing trap density via controlling thermal annealing time leads to the stabilized PCE of 18.84% from the normal planar structured FA_0.9Cs_0.1PbI₃ PSK solar cell.