Silicon solar cells with bifacial metal oxides carrier selective layers

Silicon heterojunction (SHJ) solar cells, constructed with hydrogenated amorphous silicon (a-Si:H) carrier-selective layers and a crystalline silicon substrate, are promising alternatives to conventional monocrystalline silicon solar cells. However, the undesirable characteristics like high parasitic light-absorption and low conductivity of the doped a-Si:H carrier limit further improvement of the performance of SHJ solar cells. In our design, MoOx is chosen as the hole-selective layer of the silicon heterojunction solar cell to reduce the parasitic incident-light absorption. In particular, lightly boron-doped zinc oxide (ZnO:B) films with high conductivities and low refractive indices, instead of the common heavily phosphorus-doped a-Si:H (n(+)-a-Si:H), are directly deposited as electron-selective layers to achieve low resistivity ohmic contact and an excellent optical back-reflectance. Compared to the solar cell based on an n(+)-a-Si:H electron-selective layer, efficiencies up to 16.6% could be achieved for the cells based on the ZnO:B electron-selective layer, with a relative increase in the efficiency by 15.3%. The results demonstrate that the low-cost ZnO:B electron-selective materials could allow realization of the optical and electrical requirements simultaneously, and also provide an alternative design concept for existing energy conversion devices.