Hot-carrier harvesting in hybrid metal halide perovskites for solar cells
Photovoltaic cells incorporating hybrid organic inorganic metal halide perovskites have seen a phenomenally rapid improvement over the past 5 years, with power conversion efficiencies (PCE) now exceeding 20%. An understanding of the fundamental photophysics enabling such success is only just emerging, yet such knowledge is critical for the design of high-performance materials because the generation, relaxation and recombination of photoexcited charge species have a direct bearing on how effectively light is converted into electrical current. Recent studies have suggested that charge-carrier cooling is a relatively slow process in these materials (compared to GaAs) opening the exciting prospect of hot-carrier harvesting that may allow PCEs beyond the Shockley-Queisser Limit. In this project, investigations will examine the fundamental processes of hot-charge cooling on hybrid perovskites and subsequently design and implement strategies that allow the excess energy available from hot carriers to be harvested.
Absorption of sunlight by a perovskite sensitizer in a photovoltaic application will initially create electron-hole pairs with energy significantly above the band edge. In the early stages, the excited charge-carrier distribution will be out of equilibrium and subsequently relax through a range of different processes towards the band edge and establish a thermalized Maxwell distribution characterized by a carrier temperature Tc. This project will examine and utilize such processes through two distinct aims and stages, which in combination will examine the potential of hybrid perovskites for hot-charge-carrier harvesting. First we will establish the fundamental time scales and mechanisms of carrier cooling using femtosecond spectroscopy tools. Subsequently we will design and explore suitable interfaces for hot-carrier energy harvesting they can be implemented in high-efficiency solar cells.