Graphene oxide passivation of perovskite solar cells

Abstract

Perovskite Solar cells (PSCs) are solution-processable, low-cost, highly efficient photovoltaic devices which have been rapidly developed into one of the most promising next-generation solar technologies, with advantages over incumbent silicon-based technologies which, if realised, may herald a new era in solar power generation. Obstructing the scale-up of this technology are several instability issues. Irreversible degradation of perovskite light absorbers in atmospheric conditions results in efficiency decreasing unacceptably quickly over time. Facile ionic migration within the material results in hysteretic behaviour, making accurate characterisation challenging and negatively impacting electronic transport within the absorber layer. Methylammonium lead iodide (MAPI), the archetypal perovskite, is herein grown as thin films and incorporated with graphene oxide (GO) flakes to form a composite (MAPIGO), using a one-step aerosol-assisted chemical vapour deposition (AACVD) technique. Successful deposition of GO using AACVD and its incorporation into a MAPIGO composite is demonstrated. GO is found to slow the rate of iodine and nitrogen loss in MAPIGO compared to a MAPI film without GO, as measured using X-ray photoelectron spectroscopy (XPS). It is suggested that the presence of GO stabilises the methylammonium cation, limiting degradation. An experimental procedure for the real-time measurement of iodide migration is developed and used to demonstrate the facile movement of iodide ions and vacancies in a perovskite thin film. Estimates are made of the mobility and diffusion coefficient of iodide vacancies in MAPI ((8.8 +- 3.3) x10^-10 cm^2V^-1s^-1 and (1.2 +- 1.2)x10^-9 cm^2V^-1s^-1 respectively) and MAPIGO ((1.1+-0.3)x10^-9 cm^2s-1 and (1.2 +- 1.4) x10^-9 cm^2s^-1 respectively) from subsequent HAXPES measurements. These estimates are found to be not significantly different between the two measured samples. The possible reasons for this are discussed and routes to further optimise the experimental procedure are put forward.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrew Thomas (Supervisor), Wendy Flavell (Supervisor) & David Lewis (Supervisor)