Aerosol processing of halide perovskites

Abstract

Organo-metal halide perovskites (OMHPs) research has progressed rapidly, with photovoltaic (PV) devices reaching over 20% efficiency. However, scalable production of these devices is an ongoing challenge. This study demonstrated the ability to grow halide perovskite films via aerosol assisted chemical vapour deposition (AACVD). AACVD is a scalable deposition process and one advantage of this method compared to conventional CVD is the fact that the precursors do not need to be vapourised. This allows for lower operating temperature, less complex equipment, and therefore lower overall cost. In this thesis, Methylammonium lead-triiodide (MAPI) films were deposited by sequentially passing aerosolized precursor solvent solutions into a reactor containing a heated substrate. In this study two different precursor systems were utilized, one based on lead iodide and the other on lead acetate. The first produced thick films, which were characterized extensively using X-ray diffraction, UV-visible spectroscopy, Kelvin probe measurements, ambient photoemission spectroscopy, time of flight measurements and Hall effect measurements. The second system allowed for the deposition of thinner films, more suitable for photovoltaic applications. These films were again extensively characterised but also allowed for the fabrication of the first working OMHP device utilising AACVD. Furthermore, this study demonstrated an ability to use aerosols as a scalable post-deposition treatment on existing films, modulating the morphology and boosting the performance of conventionally spin-coated films to over 20% PCE. Treatment of films was accomplished by exposing spin-coated films to aerosolised solvents. Using these treatments, it is shown that the morphology of the films can be drastically and controllably improved. This study also reveals improvements in charge carrier lifetimes and a general improvement in most (PV) parameters. This has further led to experimentation with HTL-free devices and thick OMHP layers, with both showing significant improvements after the aerosol treatment.