Significant Improvement of Conversion Efficiency by Passivation of Low-Angle Grain Boundaries in Flexible Low-Cost Single-Crystal-Like Gaas Thin-Film Solar Cells Directly Deposited on Metal Tape

We develop an easily implementable yet effective process to achieve high power conversion efficiency (PCE) in newly-developed flexible single-crystal-like GaAs thin-film photovoltaic solar cells (PVSCs) on cheap metal tape. We study various techniques on the fabricated devices to passivate the defect states associated with dangling bonds at low-angle grain boundaries (LA-GBs) existing in the single-crystal-like GaAs material. We report that sulfur by trioctylphosphine sulfide (TOP:S) solution treatment can partially but effectively passivate the defect states at the LA-GBs to increase all the SC performance parameters of open-circuit voltage VOC (33.2%), short-circuit current JSC (19.5%), and fill factor FF (25.8%), resulting in the improvement of the PCE more than double. The material and device characterizations and numerical modeling are performed to propose a mechanism, also suggesting that the PCE higher than 20%, which is an important target milestone in emerging SC technologies, can be achieved. This work presents the first effective passivation of the bulk defects in GaAs at the device level and can also offer a solution for other photonic and electronic devices using non-single-crystalline GaAs films for flexible electronics