Stable Dopant-Free Asymmetric Heterocontact Silicon Solar Cells with Efficiencies above 20%

Development of new device architectures and process technologies is of tremendous interest in crystalline silicon (c-Si) photovoltaics to drive enhanced performance and/or reduced processing cost. In this regard, an emerging concept with a high-efficiency potential is to employ low/high work function metal compounds or organic materials to form asymmetric electron and hole heterocontacts. This Letter demonstrates two important milestones in advancing this burgeoning concept. First, a high-performance, low-temperature, electron-selective heterocontact is developed, comprised of a surface passivating a-Si:H layer, a protective TiO_x interlayer, and a low work function LiF_x/Al outer electrode. This is combined with a MoO_x hole-selective heterocontact to demonstrate a cell efficiency of 20.7%, the highest value for this cell class to date. Second, we show that this cell passes a standard stability test by maintaining >95% of its original performance after 1000 h of unencapsulated damp heat exposure, indicating its potential for longevity.