Downshifting Encapsulant: Optical Simulation Evaluation of the Solution to Ultraviolet-Induced Degradation in Silicon Heterojunction Solar Cells

Abstract

Ultraviolet (UV)-induced degradation (UVID) poses a significant challenge for the prospective mass production of silicon heterojunction (SHJ) solar cells, known for their high efficiency. In this study, the magnified impact of UV radiation when employing a silicon carbide (SiC)-based transparent passivating contact (TPC) on the front side of SHJ solar cells is reported. A reduction in open-circuit voltage (V_OC), short-circuit current (J_SC), and fill factor of 12%, 6%, and 11%, respectively, is observed after UV exposure. Conventional UVID mitigation measures, UV-blocking encapsulation, are assessed through single-cell TPC laminates, revealing an unavoidable tradeoff between current loss and UVID. Alternatively, the utilization of ultraviolet-downshifting (UV-DS) encapsulants is proposed to convert UV radiation into the visible light spectrum. An optical simulation method, conducted via OPAL2, is presented to evaluate UV-DS encapsulants for diminishing UVID in SHJ solar cells with different front contacts. A simple methodology is proposed to mimic the optical property of UV-DS encapsulants. In the simulation results, additional current gains of up to 0.33 mA cm⁻² achievable with suitable UV-DS encapsulants are highlighted. The factors related to the UV-DS effects are evaluated and the optimization pathway for UV-DS encapsulants is elucidated.