Nanoscale charge accumulation and its effect on carrier dynamics in tri-cation perovskite structures

TL;DR

This study uses advanced microscopy to explore nanoscale charge behaviors in mixed-cation perovskites, revealing how charge trapping, slow relaxation, and heterogeneity affect device performance and stability.

Contribution

It provides new insights into nanoscale charge dynamics and electrostatic effects in multi-cation perovskites, linking microscopic phenomena to macroscopic device performance.

Findings

Strong negative charge trapping upon illumination

Slow charge relaxation at grain boundaries

Charge diffusion towards boundaries and heterogeneity effects

Abstract

Nanoscale investigations by scanning probe microscopy have provided major contributions to the rapid development of organic-inorganic halide perovskites (OIHP) as optoelectronic devices. Further improvement of device level properties requires a deeper understanding of the performance-limiting mechanisms such as ion migration, phase segregation and their effects on charge extraction both at the nano- and macroscale. Here, we have studied the dynamic electrical response of Cs0.05(FA0.83-MA0.17)0.95PbI3-xBrx perovskite structures by employing conventional and microsecond time-resolved Kelvin probe force microscopy (KPFM). Our results indicate strong negative charge carrier trapping upon illumination and very slow (>1s) relaxation of charges at the grain boundaries. The fast electronic recombination and transport dynamics on the microsecond scale probed by time-resolved KPFM show diffusion of charge carriers towards grain boundaries and indicate locally higher recombination rates due to intrinsic spatial heterogeneity. The nanoscale electrostatic effects revealed are summarized in a collective model for mixed-halide CsFAMA. Results on multilayer solar cell structures draw direct relations between nanoscale ionic transport, electron accumulation, recombination properties and the final device performance. Our findings extend the current understanding of complex charge carrier dynamics in stable multi-cation OIHP structures.