Temperature-dependent charge transport in solution-processed perovskite solar cells with tunable trap concentration and charge recombination

Abstract

Here we investigate temperature-dependent charge transport in solution-processed methylammonium lead triiodide (MAPbI₃) perovskite thin films with steady-state mobility measurements. Based on control of the thickness (L) of the MAPbI₃ films, one attains tunability in the carrier mobility, trap density and recombination that lead to alterations in the device characteristics. We find that the increased hole mobility in MAPbI₃ with incremental variations in L is associated with reduction in the trap concentration and Shockley–Read–Hall (SRH) recombination. By interrogating the ideality factor, we identify that the SRH charge recombination is present in the optimal solar cell. Of interest, the impact of traps on recombination becomes weakened and eventually is overwhelmed by bimolecular recombination with increasing L. Photoluminescence decay kinetics reveal that the PL related to surface and bulk recombination is longer-lived at larger L, in line with the results based on electrical analysis. The meliorated transport properties with reduced charge trapping in MAPbI₃ films can correlate to the slightly enhanced crystallinity and homogeneity in the grain size distribution in thicker films. The combinatorial study shows that the transport properties alongside traps in MAPbI₃ films are tunable simply by the physical parameter of L. Meanwhile, our work points to the necessity to further reduce the trap density so as to boost the photovoltaic performance using perovskite thin films.