PhD Student in Photovoltaic and Optoelectronic Device group (Prof. H.J. Snaith, FRS) and Terahertz Photonics group (Prof. M.B. Johnston), mostly focusing on understanding the fundamental physics of perovskites via a combination of experimental work and computational modelling, and developing new measurement methodologies that give accurate device characterization and will help device optimisation in optoelectronic applications.
Semiconductor Physics, Perovskite Technology
ACS Energy Letters American Chemical Society 5 (2020) 376-384
Physical Review Applied, 15, 1, 2021, 014006
Hybrid halide perovskites have great potential for application in optoelectronic devices. However, understanding of some basic properties, such as charge-carrier transport, remains inconclusive, mainly due to the mixed ionic and electronic nature of these materials. Here, we perform temperature-dependent pulsed-voltage space-charge limited current measurements to provide a detailed look into the electronic properties of MAPbBr3 and MAPbI3 single crystals. We show that the background carrier density in these crystals is orders of magnitude higher than expected from thermally excited carriers from the valence band. We highlight the complexity of the system via a combination of experiments and drift-diffusion simulations, and show that different factors, such as thermal injection from the electrodes, temperature dependent mobility and trap and ion density influence the free carrier concentration. We experimentally determine effective activation energies for conductivity of 349 ± 10 meV for MAPbBr3 and 193 ± 12 meV for MAPbI3, which includes the sum of all these factors. We point out that fitting the dark current-density voltage curve with a drift-diffusion model allows for the extraction of intrinsic parameters such as mobility and trap and ion density. From simulations, we determine a charge carier mobility of 12.9 cm2/Vs, a trap density of 1.52 x 1013 cm-3, and an ion density of 3.19 x 1012 cm-3 for MAPbBr3 single crystals. The insights on charge carrier transport in metal halide perovskite single crystals will be beneficial for device optimization in various optoelectronic applications.