  Great achievements in last five years, such as record-efficient
amorphous/crystalline silicon heterojunction (SHJ) solar cells and cutting-edge
perovskite/SHJ tandem solar cells, place hydrogenated amorphous silicon
(a-Si:H) at the forefront of emerging photovoltaics. Due to the extremely low
doping efficiency of trivalent boron (B) in amorphous tetravalent silicon,
light harvesting of aforementioned devices are limited by their fill factors
(FF), which is a direct metric of the charge carrier transport. It is
challenging but crucial to develop highly conductive doped a-Si:H for
minimizing the FF losses. Here we report intensive light soaking can
efficiently boost the dark conductance of B-doped a-Si:H "thin" films, which is
an abnormal Staebler-Wronski effect. By implementing this abnormal effect to
SHJ solar cells, we achieve a certificated power conversion efficiency (PCE) of
25.18% (26.05% on designated area) with FF of 85.42% on a 244.63-cm2 wafer.
This PCE is one of the highest reported values for total-area "top/rear"
contact silicon solar cells. The FF reaches 98.30 per cent of its
Shockley-Queisser limit.
