Unveiling the mechanism of ultraviolet-induced degradation in silicon heterojunction solar cells

UV-induced degradation (UVID) poses a serious concern in silicon heterojunction (SHJ) solar cells when operating in the field. Herein, the root cause of UVID of bare SHJ solar cells was investigated. It was found that the major degradation occurs in open-circuit voltage (Voc) V oc ) and fill factor (FF) FF ) during UV exposure. The evident increase in series resistance (Rs) R s ) is the primary cause of FF degradation. The reduced content of Si-H bonds and the increased pore structure in both intrinsic hydrogenated amorphous silicon (i-a-Si:H) and phosphorus-doped hydrogenated microcrystalline silicon oxide (n-mu c-SiOx:H) x :H) layers lead to the deterioration of H atoms chemical passivation on the crystalline silicon (c-Si) surface. Additionally, the motion of H atoms from the breakage of Si-H bonds reacts with P dopant atoms to form inactive P-H bonds in the n-mu c-SiOx:H x :H layers, which not only poisons field-effect passivation but also significantly reduces the conductivity of the films. Interestingly, an elevated temperature-assisted intensive light soaking can recover the UV-damaged H-passivation and P-doping effect. As a result, the performance of SHJ solar cell is significantly restored. These findings have important implications for understanding UV-induced degradation in SHJ solar cells.