Mechanism of photon-induced performance changes in silicon heterojunction solar cells

Short-wavelength ultraviolet (UV) photons adversely affect hydrogenated amorphous silicon thin films, as well as on silicon heterojunction (SHJ) solar cells and modules. This research examines the impact and mechanisms of photon-induced performance changes. UV A exposure disrupts Si–H bonds, significantly reducing hydrogen content in both intrinsic and doped hydrogenated amorphous silicon (a-Si:H) films. This disruption impairs the interface passivation effect, leading to the degradation of SHJ solar cells and modules, primarily indicated by a decrease in open-circuit voltage (V_oc) and fill factor (FF). UV irradiation from the front side of SHJ solar cells reduces V_oc and FF by 1.38% and 2.28%, respectively, resulting in a 2.28% efficiency decline. Cells irradiated from the backside show decreases in V_oc and FF of approximately 1.96% and 2.73%, respectively, leading to an overall efficiency reduction of approximately 3.58%. However, subsequent light-soaking increases V_oc and FF by approximately 0.96% and 1.37%, respectively, for frontside-irradiated cells, achieving an overall efficiency improvement of approximately 2.51%. Thus, light-soaking effectively recovers performance losses caused by UV irradiation in SHJ solar cells. This research clarifies the mechanisms influencing the performance of a-Si:H thin films, SHJ solar cells, and modules under UV irradiation and light-soaking, offering significant contributions towards the development of highly efficient and reliable SHJ devices.