The bifunctional tin-doped indium oxide as hole-selective contact and collector in silicon heterojunction solar cell with a stable intermediate oxide layer

The tin-doped indium oxide (ITO) and the intermediate nanometer-scale SiOx layers were synthesized directly on n-type crystalline silicon (n-Si) substrate by radio-frequency magnetron sputtering deposition. During the ITO-sputtering deposition, the effect of shallow implantation intermixing led to forming an ultra-thin SiOx layer, which could successfully lessen the interface states and promote the transportation of carriers. The photovoltaic properties of devices showed the open-circuit voltage (Voc) strongly correlated to the carrier concentration of ITO (nITO), indicating a hole-selective contact of ITO. An equivalent “p-type Fermi level” (hole as majority carriers) was reasonably employed to interpret the decrease of Voc with the increase of nITO. The impact of the work function difference between ITO and n-Si on Voc of ITO/SiOx/n-Si heterojunction cells was tentatively equivalent to the difference of the defined quasi-Fermi levels. Through the modification of surface-reflectance and rear contact, the heterojunction structure solar cells achieved efficiency of 11.50 ± 0.17%. Furthermore, the stability of the devices in conversion efficiency was excellent over a whole year. The temperature coefficient of −0.34%/°C was obtained, which was better than −0.45%/°C of a typical diffused-junction silicon solar cell.