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Silicon heterojunction (SHJ) solar cells hold the power conversion efficiency (PCE) record among crystalline solar cells. However, amorphous silicon is a typical highentropy metastable material. Damp-heat aging experiments unveil that the amorphous/crystalline silicon interface is susceptible to moisture, which is potentially the biggest stumbling block for mass production. By capping SiN x and SiO x dielectrics, the absolute PCE degradation is predicted to be only 0.6% after a 30-year installation. This demonstrates the SHJ solar cell is a highly promising candidate for next-generation photovoltaics.

Recent achievements in amorphous/crystalline silicon heterojunction (SHJ) solar cells and perovskite/SHJ tandem solar cells place hydrogenated amorphous silicon (a-Si:H) at the forefront of photovoltaics. Due to the extremely low effective doping efficiency of trivalent boron in amorphous tetravalent silicon, light harvesting of aforementioned devices is limited by their fill factors (FFs), a direct metric of the charge carrier transport. It is challenging but crucial to develop highly conductive doped a-Si:H with minimal FF losses. Here we report that light soaking can efficiently boost the dark conductance of boron-doped a-Si:H thin films. Light induces diffusion and hopping of weakly bound hydrogen atoms, which activates boron doping. The effect is reversible and the dark conductivity decreases over time when the solar cell is no longer illuminated. By implementing this effect to SHJ solar cells, we achieved a certified total-area power conversion efficiency of 25.18% with a FF of 85.42% on a 244.63 cm2 wafer.