ZnS thin film functionalized as back surface field in Si solar cells

A good quality ZnS thin film has been functionalized as back surface field (BSF) in Si solar cells. Compared to Si solar cells without BSF, the solar cells with ZnS BSF presents about 50% increase of the power conversion efficiency (PCE). This improvement stems from a downward energy band at the c-Si (n)/ZnS interface, which forms an interfacial field-effect. This field impedes the minority carrier recombination and favors the majority carrier transport, so that open circuit voltage and fill factor of the device are increased. Additional electrode of low work function (e.g. Mg) can further enhance the performance of the solar cell with the ZnS BSF thanks to second downward energy band at ZnS/electrode interface. This work demonstrates that the compound thin film can act as a candidate for a functional layer in Si solar cells.