Regular Article

Study of transport parameters and defect states in thin film perovskites under different environments − air or vacuum − and after light-soaking

¹ Group of Electrical Engineering from Paris, CNRS (UMR 8507), Pierre and Marie Curie University, Paris-Sud11 University, 11 rue Joliot Curie, 91190 Gif sur Yvette, France
² IPVF, Ile-de-France Photovoltaic Institute (IPVF), 30 Route Départementale 128, 91120 Palaiseau, France

^* e-mail: longeaud@geeps.centralesupelec.fr

Received: 15 October 2019
Received in final form: 11 November 2019
Accepted: 5 December 2019
Published online: 26 February 2020

Abstract

We present some advanced characterization techniques developed to investigate on the opto-electronic properties of thin film semiconductors and apply them to perovskite layers. These techniques are the steady state photocarrier grating (SSPG) and the Fourier transform photocurrent spectroscopy (FTPS). The SSPG was developed to study the ambipolar diffusion length of carriers and the FTPS was imagined to measure the variations of the below gap absorption coefficient with the light energy, giving information on the defect densities of the gap responsible for this absorption. The potentialities of these techniques are first detailed and then exemplified by their application to thin film perovskites. To study their stability, these films were exposed to different environments, air or vacuum, and in their as-deposited state or after light-soaking with heavy light. We find that the diffusion length and density of states are quite stable, even after light-soaking, and suggest that the degradation of devices exposed to 1 sun mainly comes from the evolution of the contacts instead of the perovkite itself.