p-type c-Si/SnO2/Mg heterojunction solar cells with an induced inversion layer

Crystalline silicon/compounds heterojunction (SCH) solar cells using oxides or fluorides as the electron or hole transport layers present great low-cost potential. In this paper, c-Si/SnO2 SCH solar cells are based on p-type c-Si substrates and use SnO2, prepared by atomic layer deposition, as the electron transport layers are investigated. By optimizing the SnO2 thickness and the device annealing process, a Voc of 718 mV and an efficiency of 20.1% are achieved on a champion SCH solar cell with an optimized SnO2 thickness of 3 nm. By analyzing the dark J–V curves, transport mechanisms of the silicon/compound heterojunction are investigated. It is proved that a strong inversion layer is induced in the p-type Si substrate, and a high hole barrier exists in the heterojunction region, which makes it a minority-carrier device. The induced inversion layer at the Si surface and the carrier selective transport effect of the SnO2 layer together enable the devices to achieve a high Voc.