Comment on "Resolving spatial and energetic distributions of trap states in metal halide perovskite solar cells"

TL;DR

This paper critiques previous claims of low trap densities in perovskite solar cells, showing that such measurements are not physically resolvable and that observed interfacial charges are due to measurement artifacts.

Contribution

It provides a theoretical analysis demonstrating the limitations of capacitance profiling in accurately resolving trap densities in perovskite solar cells.

Findings

Bulk trap densities below 10^11 cm^-3 are not physically resolvable given the device geometry.

Apparent interfacial charge densities are explained by geometrical capacitance and charge injection effects.

Previous measurements may overestimate trap densities due to measurement artifacts.

Abstract

Ni et al. report minimum bulk trap densities of 10^11 cm-3 and 1-4 orders change in interfacial trap densities derived from drive-level capacitance profiling of lead halide perovskites. From basic electrostatic arguments, we show that such bulk trap densities cannot be resolved for a p-i-n perovskite solar cell for the reported layer thicknesses, while the apparent interfacial charge densities are a consequence of the geometrical capacitance and of charge injection into the perovskite layer.