Polaritonic enhancement of metal halide perovskite photovoltaic performance

Clean, renewable solar energy is currently most widely harnessed by silicon solar cells. Competition has emerged over the last decade in the form of halide perovskites (HPs), semiconductors whose excellent physical properties allow for highly efficient, easily fabricated solar cells. In recent years however, improvements in perovskite solar cells have slowed down, as changes to their composition and fabrication method now offer only diminishing returns.

This project will aim to improve the performance of HP solar cells by incorporation of optical cavities to form hybrid light-matter states called 'polaritons'. Optical cavities can be thought of as a trap for light, which bounces between two precisely spaced mirrors many times before escaping. Polaritons are mixed light-matter states which arise from the resonant exchange of energy between an optically bright transition in matter and the confined photonic mode of an optical cavity.

As well as having been previously exploited to achieve lasing in MHPs, the formation of polaritonic states has also been found to alter chemical reactivity in solution-phase systems. This project will apply the same principles to the enhancement of solar cell efficiencies.

The overall aim of this research is to determine how the optoelectronic properties of HPs can be enhanced by harnessing polaritonic effects arising from optical cavities. To achieve this goal, we will construct optical cavities from metallic and dielectric mirrors deposited in-house, sandwiched around HP thin films such that an electromagnetic cavity mode is resonant with the excitonic transition in the HP.

We will then use photoluminescence (PL) and reflectance spectroscopy to observe the formation of exciton-polaritons and interrogate how their presence alters the photophysical properties of the HP materials, ultimately developing quantitative models to interpret and hence control this behaviour. This ambitious project will proceed via the following objectives:

1. Reliably prepare polaritons in three-dimensional HPs. 2. Achieve rational control over the degree of polariton formation in the HP microcavities. 3. Evaluate the influence of polaritonic effects on charge-carrier dynamics in HP thin films.