Optical determination of Shockley-Read-Hall and interface recombination currents in hybrid perovskites

Abstract

Metal-halide perovskite solar cells rival the best inorganic solar cells in power conversion efficiency, providing the outlook for efficient, cheap devices. In order for the technology to mature and approach the ideal Shockley-Queissier efficiency, experimental tools are needed to diagnose what processes limit performances, beyond simply measuring electrical characteristics often affected by parasitic effects and difficult to interpret. Here we study the microscopic origin of recombination currents causing photoconversion losses with an all-optical technique, measuring the electron-hole free energy as a function of the exciting light intensity. Our method allows assessing the ideality factor and breaks down the electron-hole recombination current into bulk defect and interface contributions, providing an estimate of the limit photoconversion efficiency, without any real charge current flowing through the device. We identify Shockley-Read-Hall recombination as the main decay process in insulated perovskite layers and quantify the additional performance degradation due to interface recombination in heterojunctions.

On the Relation between the Open‐Circuit Voltage and Quasi‐Fermi Level Splitting in Efficient Perovskite Solar Cells

“…While the absolute locations of E F,e and E F,h are generally not accessible, the QFLS can be determined directly by means of absolute PL measurements . This methodology has been proven to be an efficient approach for quantifying recombination losses in the neat perovskite, multilayer assemblies or even complete perovskite solar cells …”

“…Generally, PLQY under steady state illumination conditions will be limited by all recombination processes, meaning that there is no trivial relation between the QFLS and J G . However, within a limited intensity interval, this relation can be written in terms of a modified diode equation …”

“…While several mechanism have been proposed to explain the V OC saturation, it still constitutes a matter of active debate. On the other hand, there are very few publications regarding the intensity dependence of the QFLS, and none of these reported a saturation of the QFLS …”

The Optical Diode Ideality Factor Enables Fast Screening of Semiconductors for Solar Cells

“…PL has been used in the past to study and predict the role of different recombination channels in the finished devices for various solar technologies. But these studies had a different purpose than our study.…”

“…In several investigations the measurements were performed on finished solar cells or the goal was to determine the recombination activity of grain boundaries or the radiative recombination coefficient . In another study an approach similar to ours was used to differentiate between bulk and interface recombination. Below we also discuss this distinction but go beyond in predicting the diode ideality factor of the finished device from the PL measurement of the absorber covered with the buffer layer alone.…”