Optoelectronics of Nanocrystals: Infrared Absorbing Lead Halide Perovskite

Abstract

Lead halide perovskites (LHPs) have become increasingly popular as the base material in solar cells and other optoelectronic devices due to their defence tolerant structure leading to high power conversion efficiency and high photoluminescence quantum yield. They are wide band gap materials absorbing and emitting in UV-visible range. Hence, solar cells made from LHPs do not work at full potential as they are unable to absorb the IR part of the solar spectrum. Formamidinium Lead Iodide (FAPI) has the smallest band gap and relatively high stability among commonly used LHPs. The aim of this thesis is to develop a material using FAPI that absorbs IR radiation while maintaining the transport properties of lead halide perovskites. This is achieved by doping PbS colloidal quantum dots (CQDs) in FAPI nanocrystals. LHPs nanocrystals were synthesised using different methods, and the effect of their size, shape, and composition on the band gap was studied. Characterisation of FAPI nanocrystals was done to study its structure. Films of FAPI nanocrystals were deposited on gold interdigitated electrodes, and transport properties were studied. Evidence of trap free band gap of FAPI was obtained by studying the photocurrent dependence on illumination power and dark current variation with temperature. Lastly, a hybrid material was created by mixing FAPI nanocrystals and PbS CQDs. By studying the evolution of dark current and photocurrent with increase in PbS doping, 35% PbS was identified as the optimal PbS doping amount. In the end, XPS measurements were done to explore the electronic structure of FAPI, PbS and the new hybrid material.