Large-Area Printed Metal Halide Perovskite Solar Cells

Metal halide perovskites (MHPs) are one of the most promising materials in solar industry. They are solution processed and have high light absorption coefficient and long electron-hole diffusion length. However, there are several current challenges to commercialize MHPs solar cells, one of which is that it is difficult to scale up the fabrication of MHPs thin film using the current spin coating, while roll-to-roll process is needed to fabricate solar cells on an industrial scale. Roll-to-roll process of perovskite solar cells can be achieved by overcoming the two challenges described below.
In the first part of the study, in order to achieve high-throughput roll-to-roll manufacturing of flexible perovskite solar cells, low temperature processing of all device layers are realized. The most commonly used electron transporting layer in high-performance perovskite solar cells are TiO2 thin films and SnO2 thin film processed at high temperature (450 °C and 180 °C respectively). Therefore, I designed the low temperature processes to fabricate these two kinds of metal oxide, TiOx and SnO2 thin film. Flexible solar cells fabricated with these thin films with decent power conversion efficiency are demonstrated.
In the second part, in order to achieve scalable fabrication of perovskite optoelectronic devices, large area deposition techniques such as solution shearing are realized. The mechanisms of fabrication processes are also studied in different solution shearing regimes. By monitoring the precursor species during crystallization process using In-situ Grazing Incidence Wide-Angle X-ray Scattering, the crystallization process in low shearing speed meniscus regime is proven to happen under lower supersaturation. The low supersaturation contributes to the bigger crystal size of thin film under lower shearing speed. Photodetectors with perovskite thin films coated at low shearing speed meniscus regime show much higher internal quantum efficiency because of the larger crystal domain size and uniform orientation inside of domains. This shows continuing study and rational design of the crystallization process is needed to push perovskite technology toward useful applications.