Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
DOI: https://doi.org/10.29363/nanoge.hopv.2022.196
Publication date: 20th April 2022
Layered metal halide perovskites have been investigated for use in a range of optoelectronic devices including photovoltaic cells. Their main appeal for photovoltaics is improved aqueous stability, which is enabled by their incorporation of larger organic cations which result in the formation of Ruddlesden-Popper and other related phases. However, quantum and dielectric confinement effects increase the exciton binding energies in these materials to as much as 100s of meV [1]. These increased binding energies correspond to an increase in exciton population at ambient temperatures which can decrease effective charge-carrier mobilities and significantly shorten charge-carrier lifetimes [1]. As such, optical-pump/THz-probe (OPTP) spectroscopy and other ultrafast spectroscopic techniques are used to elucidate the interplay between free charges and excitons in PEAPbI4 (PEA = phenylethylammonium) and comment on the limits these properties impose on charge transport in devices. Furthermore, several synthetic strategies have been implemented to balance the desired effects of improved stability with worsened optoelectronic properties, suggesting a balance between excitons and free charges is achievable by tuning the composition. These strategies include mixing larger and smaller cations [2], adding smaller amounts of layered materials alongside more standard 3D materials [3], and incorporating additives [4]. A comparison of the ultrafast optoelectronic properties of these materials reveals their complex sensitivity to these various approaches, including the effects on charge-carrier mobility, lifetimes, and doping density.