Halide perovskites are exceptionally promising materials for optoelectronic applications, and have already been incorporated into efficient photovoltaic devices, light-emitting diodes and lasers. However, despite the skyrocketing efficiencies of perovskite-based devices, there is insufficient understanding of the fundamental processes governing crystallisation and defect formation in perovskite-thin films.This project involves research at the intersection of chemistry, solid-state physics, and materials science, geared towards achieving the following goals: 1) developing a fundamental understanding of the colloidal chemistry, and solvent-solute interactions of perovskite precursor inks, 2) elucidating the mechanisms of nucleation, crystallisation and defect formation of thin-films, 3) developing methods to reduce defect formation and mitigate its effects, and 4)
the development of stable and efficient photovoltaic devices and light-emitting diodes.
Halide perovskites are a synthetic sub-category of perovskite materials which have generated much interest due to their remarkable optoelectronic properties (i.e. broad absorption over the visible spectrum, long carrier diffusion lengths, ambipolar transport, high charge-carrier mobilities etc.) and the ability to produce high-quality material through facile, solution-based processing. In just under a decade, perovskite-based optoelectronics have achieved certified photovoltaic power conversion efficiencies (PCEs) exceeding 25% on a labscale, surpassing all other competing emerging photovoltaic technologies and approaching the performances of mature thin-film technologies. In perovskite optoelectronics research, while efficiency records are regularly broken, there is a lack of detailed understanding of the fundamental processes which govern crystallisation and defect formation in perovskite thin films. This is of paramount importance as, for the same composition material, different crystallisation strategies have been shown to produce films with significantly different optoelectronic properties, defect concentrations and even stability. In the absence of a firm grasp of the mechanisms of crystallisation and defect formation, the various interventions which have been applied to control perovskite crystallisation and passivate electronic and structural defects have been largely carried out through a trial and error, top-down approach. The proposed research aims to carry out a bottom-up investigation which yields a fundamental understanding of the perovskite crystallisation process, and hence provides the ability to control, optimise and tailor the optoelectronic properties of perovskite thin-films. Further, this will allow for minimising structural and electronic defects, having important implications, not just for improving both the performance and stability of perovskite photovoltaics, but for all perovskite-based optoelectronics. This project aims to develop an understanding the chemistry of the perovskite precursor solutions, map the conversion processes from precursor solution to crystal grains, and identify how manipulating the chemistry of the precursor solution, grain boundaries and interfaces affects the nature and concentration of the defects, and the chemical composition and optoelectronic properties of perovskite thin-films. An important aspect of this approach is starting on a fundamental microscopic level and then translating the understanding of the relevant processes into macroscopic properties. The ability to understand and control these material systems will not only lead to significant improvements in the performance of perovskite optoelectronic devices, but also allow for rational design of new solvent systems, and new approaches to controlling the crystallisation of halide perovskite materials.
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