A Non-destructive UV Raman Characterisation Platform to Enable Insight into the Mechanism of Reversible Ultraviolet-Induced Degradation (UVID) in TOPCon Solar Cells

Abstract

Ultraviolet light-induced degradation (UVID) has been reported across mainstream highefficiency Silicon (Si) solar cell architectures, including heterojunction (HJT), passivated emitter and rear cell (PERC) and tunnel oxide passivated contact (TOPCon) solar cells, causing up to 10% efficiency loss after continuous exposure to high UV doses.Encouragingly, this degradation has also been reported to be recoverable under certain conditions, such as light soaking. However, in the absence of a clear mechanistic understanding of both the degradation and recovery process, current testing protocols and stability metrics fall short of capturing the true UV resilience of these devices. Establishing a fundamental understanding of UVID is therefore critical for developing more predictive testing frameworks and durable cell architectures under real-world operating conditions. In this work, we demonstrate that the UVID of TOPCon silicon solar cells can be effectively recovered using light soaking in the first place. The recoverable macroscopic cell performance is subsequently found correlated with two reversible changes at the materials level: front surface reflectance by optical transmission of SiNx and a Boron-doped Si Raman peak by UV Raman spectroscopy. With further atom probe tomography (APT) investigation and theoretical modeling, the mechanisms of this reversible UVID and light soaking induced recovery (LSIR) process are identified. The elucidation of the reversible UVID mechanism at the atomic level directly informs the development of effective mitigation strategies. We demonstrate that the synchronous use of a thick AlOx film and a low Si:N ratio SiNx layer can improve the UVID resistance of TOPCon solar cells. Moreover, the non-destructive material level characterisation platform established in this work enables effective capture of the degree of UVID resistance in the design of durable TOPCon solar cells with the potential of in-line quality control.