Probing the ionic defect landscape in halide perovskite solar cells

Sebastian Reichert,Qingzhi An,Carsten Deibel,Yana Vaynzof,Aron Walsh,Young-Won Woo

doi:10.1038/s41467-020-19769-8

Abstract

Point defects in metal halide perovskites play a critical role in determining their properties and optoelectronic performance; however, many open questions remain unanswered. In this work, we apply impedance spectroscopy and deep-level transient spectroscopy to characterize the ionic defect landscape in methylammonium lead triiodide (MAPbI3) perovskites in which defects were purposely introduced by fractionally changing the precursor stoichiometry. Our results highlight the profound influence of defects on the electronic landscape, exemplified by their impact on the device built-in potential, and consequently, the open-circuit voltage. Even low ion densities can have an impact on the electronic landscape when both cations and anions are considered as mobile. Moreover, we find that all measured ionic defects fulfil the Meyer–Neldel rule with a characteristic energy connected to the underlying ion hopping process. These findings support a general categorization of defects in halide perovskite compounds.

Highlights

Point defects in metal halide perovskites play a critical role in determining their properties and optoelectronic performance; many open questions remain unanswered
To controllably tune the defect landscape in MAPbI3 perovskite solar cells, we exploited the method developed by Fassl et al42. to fabricate a series of samples from precursor solutions with gradually changing stoichiometry
We start by intentionally preparing an understoichiometric solution, in which a slight deficiency of methylammonium iodide (MAI) is expected to result in films rich in vacancies such as

Summary

Introduction

Point defects in metal halide perovskites play a critical role in determining their properties and optoelectronic performance; many open questions remain unanswered. 1234567890():,; Triggered by the first demonstration of a perovskite solar cell in 20091, significant research efforts have been devoted to the field of perovskite photovoltaics leading to a record power conversion efficiency of 25.5%2 This remarkable performance is made possible by a combination of advantageous properties of perovskite materials, among which most noteworthy are their low exciton binding energies, high absorption coefficients, high charge carrier diffusion lengths and correspondingly long lifetimes of free charge carriers[3,4,5,6]. Significant progress has been made over the last decade in the development of novel fabrication methods and device architectures as well as optimization by interfacial engineering[7,8,9,10,11] Despite these advancements, several aspects of perovskite solar cells remain a challenge. Perovskites are interstitials such acshaI ÀirgeadndvaMcaAnþi c2ie3s–,26s.uEcxhpearsimVeþIntaalnlyd, ionic defects and their migration have been observed by a range of methods[27,28,29]

Methods

Results

Conclusion