Understanding losses in halide perovskite thin films

We find semiconductor at the heart of every electronic device such as microprocessor chip, transistor, as well as light-emitting diode (LED) which has become part of our 21st century society. The main impetus of the semiconductor deployment came after several ground breaking experiments by W.B. Shockley, J. Bardeen, and W.H. Brattain (Nobel prize in 1956), and followed by dedicated studies on semiconductor growth for LED by I. Akasaki, H. Amano, and S. Nakamura (Nobel prize in 2014). This closer the gap between our knowledge in solid-state physics semiconductor and light science (nanophotonics). On the other hand, advances in thin-film (submicron thick) semiconductor technology will also find applications in highly efficient and low-cost photovoltaics. Hybrid-halide perovskites have emerged over the unprecedented time frame over the last 6 years as a promising class of materials for such applications. Most notably, their solar cells have achieved power conversion efficiencies above 20% in the laboratory, even though many fundamental questions still remain unanswered. Therefore for halide perovskite thin-films to have an impact beyond the laboratory requires a systematic understanding and eliminating sources of losses. One important finding in this thesis is that a variable grain boundary character can explain the mysteriously long lifetime and record efficiency achieved in small grain halide perovskite thin films. Furthermore, this thesis outline the methodology used to improve our understanding, while pointing the way forward to eliminate the losses and demonstrating a novel architecture design to even better devices.