Unravelling the low-temperature metastable state in perovskite solar cells by noise spectroscopy.

C Barone,S Pagano,N H Nickel,H C Neitzert,J Rappich,F Lang,C Mauro,B Rech,G Landi

doi:10.1038/srep34675

Abstract

The hybrid perovskite methylammonium lead iodide CH3NH3PbI3 recently revealed its potential for the manufacturing of low-cost and efficient photovoltaic cells. However, many questions remain unanswered regarding the physics of the charge carrier conduction. In this respect, it is known that two structural phase transitions, occurring at temperatures near 160 and 310 K, could profoundly change the electronic properties of the photovoltaic material, but, up to now, a clear experimental evidence has not been reported. In order to shed light on this topic, the low-temperature phase transition of perovskite solar cells has been thoroughly investigated by using electric noise spectroscopy. Here it is shown that the dynamics of fluctuations detect the existence of a metastable state in a crossover region between the room-temperature tetragonal and the low-temperature orthorhombic phases of the perovskite compound. Besides the presence of a noise peak at this transition, a saturation of the fluctuation amplitudes is observed induced by the external DC current or, equivalently, by light exposure. This noise saturation effect is independent on temperature, and may represent an important aspect to consider for a detailed explanation of the mechanisms of operation in perovskite solar cells.

Highlights

Among the available non-destructive characterization techniques, noise spectroscopy has demonstrated its effectiveness in the investigation of advanced photovoltaic and innovative materials[18,19,20,21]
In the case of perovskite solar cell devices, where a phase transition from a tetragonal to an orthorhombic structure has been observed near 160 K26, noise measurements can be a very useful experimental technique, considering that no clear signature of such a transition is evident in the cell DC properties
Hybrid perovskites are an ideal absorber for solar cells, but show various structural transitions upon temperature

Summary

Introduction

Among the available non-destructive characterization techniques, noise spectroscopy has demonstrated its effectiveness in the investigation of advanced photovoltaic and innovative materials[18,19,20,21]. In the case of perovskite solar cell devices, where a phase transition from a tetragonal to an orthorhombic structure has been observed near 160 K26, noise measurements can be a very useful experimental technique, considering that no clear signature of such a transition is evident in the cell DC properties. The reported results shine light on the role played by excitons in the photoexcited carrier dynamics, and on the temperature dependence of localization effects, including phonon coupling and charge carrier trapping[27,28]. These phenomena need to be clarified, because of their potential to influence the efficiency of charge transport within the perovskite film

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Conclusion