Elucidating the role of disorder and free-carrier recombination kinetics in CH3NH3PbI3 perovskite films.

Chan La-O-Vorakiat,Elbert E M Chia,Rudolph A Marcus,Haibin Su,Huanxin Xia,Gagik G Gurzadyan,Maria-Elisabeth Michel-Beyerle,Reinhard Haselsberger,Liang Cheng,Jeannette Kadro,Mai-Thu Khuc,Yeng Ming Lam,Teddy Salim

doi:10.1038/ncomms8903

Abstract

Apart from broadband absorption of solar radiation, the performance of photovoltaic devices is governed by the density and mobility of photogenerated charge carriers. The latter parameters indicate how many free carriers move away from their origin, and how fast, before loss mechanisms such as carrier recombination occur. However, only lower bounds of these parameters are usually obtained. Here we independently determine both density and mobility of charge carriers in a perovskite film by the use of time-resolved terahertz spectroscopy. Our data reveal the modification of the free carrier response by strong backscattering expected from these heavily disordered perovskite films. The results for different phases and different temperatures show a change of kinetics from two-body recombination at room temperature to three-body recombination at low temperatures. Our results suggest that perovskite-based solar cells can perform well even at low temperatures as long as the three-body recombination has not become predominant.

Highlights

Apart from broadband absorption of solar radiation, the performance of photovoltaic devices is governed by the density and mobility of photogenerated charge carriers
We can perform time-resolved terahertz spectroscopy (TRTS)[7], which probes the free-carrier dynamics via the photoinduced change in the conductivity, as a function of time delay after photoexcitaton
For the perovskite films studied in this paper, our analysis reveals a significant contribution from backscattering of charge carriers due to disorder

Summary

Introduction

Apart from broadband absorption of solar radiation, the performance of photovoltaic devices is governed by the density and mobility of photogenerated charge carriers. The latter parameters indicate how many free carriers move away from their origin, and how fast, before loss mechanisms such as carrier recombination occur. Previous TRTS studies of thin perovskite films on quartz and on mesoscopic supports[8,9,10] focus on the room-temperature dynamics of free carriers obtained by measuring frequencyintegrated photoconductivity. From those measurements, only lower bounds of carrier mobilities were obtained. In our present work, we make use of the full potential of TRTS by performing a spectral analysis of Ds1(o) and Ds2(o) to analyse the photoconductivity covering a broad terahertz range from 0.5 to 2.5 THz, as a function of temperature from 15 to 285 K, where a tetragonal-to-orthorhombic structural phase transition at 162.5 K has been reported for single crystals of this material[11]

Methods

Results

Conclusion