Ultraviolet-induced degradation in TOPCon solar cells: Reversible (r-UVID) and irreversible (ir-UVID) degradation, mechanisms and mitigation strategies

Abstract

Currently, tunnel oxide passivated contact (TOPCon) solar cells are rapidly gaining market share due to their high efficiency and compatibility with existing manufacturing lines. However, ultraviolet-induced degradation (UVID) has emerged as a critical reliability concern that can cause significant power loss in these cells, especially in modules relying on hydrogen-rich front-side passivation stacks. In this paper, we refer to specific literature, briefly describe the development history of UVID, introduce the associated phenomena in crystalline silicon solar cells, and describe its characteristic features, including metastable recovery behaviors. During subsequent dark storage, the reversible UVID component triggers further performance degradation; however, such degradation can be largely recovered via light soaking or thermal annealing and imposes negligible impacts on actual power output under outdoor field operation. In addition, we analyze the fundamental causes of UVID and find that they are closely related to Si–H bond dissociation, hydrogen redistribution at the dielectric/silicon interface, and hot-carrier injection into the AlO_x layer. At present, in view of the involvement of hydrogen and dielectric properties, this paper introduces several methods to suppress UVID, such as optimizing AlO_x thickness, adopting silicon nitride and silicon oxide protective layers, tuning hydrogen content, and enhancing field-effect passivation. Finally, this paper concludes the current understanding of UVID in TOPCon devices, discusses existing challenges, and prospects future research directions.