Unraveling trap distribution in perovskite films: A qualitative analysis via diffusion to drift transition voltage of current-voltage characteristics

Traps cause accumulation of space charge near injecting contacts, due to which there is band bending in the vicinity of contacts. This leads to a lowering of voltage at which there is change from diffusion to drift dominated current under steady state, termed as transition voltage (V-alpha). We propose a technique to qualitatively understand the trap distribution by analyzing the V-alpha of a two terminal perovskite device. The validity of the proposed technique has been verified from the numerical simulations carried out using Sentaurus TCAD. Both density (N-T) and energetic depth (E-T.) of traps were varied to study their effect on V-alpha. Devices with deeper and higher N-T have been found to exhibit stronger band bending and thus lower V-alpha. In addition, V-alpha has been found to be sensitive to N-T even when band bending due to accumulated ions or uncompensated dopants near interfaces is significant. This dependence has been further illustrated for a perovskite solar cell device. It has been concluded that V-alpha can be advantageous over V-OC in optimizing perovskite film for trap-free solar cell. The availability of different methods to extract V-alpha from current-voltage (J-V) characteristics, and the extra sensitivity of V-alpha to N-T paves a way to study traps effectively.