Efficient silicon solar cells applying cuprous sulfide as hole-selective contact

The introduction of dopant-free materials used for carrier-selective contact effectively overcomes the issue of high surface recombination velocity at aluminum back surface field. Additionally, dopant-free materials have the advantages of low fabrication temperature, simple process and considerably high efficiency. In this contribution, cuprous sulfide (Cu₂S), fabricated by thermal evaporation, is applied as hole-selective contact material at rear-surface region of crystalline silicon (c-Si) solar cells for the first time. The band alignment of Cu₂S/p-Si exhibits only a small valence band offset and huge conduction band offset being excellent hole-selective and electron blocking properties. By inserting Cu₂S layer between p-Si and Ag, a lower contact resistivity of 27.2 mΩ cm² is achieved. As a result, the introduction with 4-nm Cu₂S interlayer significantly improves device efficiency to over 21%, affording a 1.2% absolute increase from the control cell. Metal sulfides introduced herein exhibit remarkable properties for carrier-selective contacts, compared to conventional metal nitrides and oxides.