Improved open-circuit voltage of silicon nanowires solar cells by surface passivation
The surface recombination at the surface of silicon nanowires (SiNWs) deteriorates the performance of SiNWs solar cells and thus the reduction of the SiNWs surface recombination becomes a crucial issue. In this paper, we observe an improved SiNW surface passivation by hydrogenated amorphous silicon (a-Si:H). The results show that a thicker i-layer results in a higher open-circuit voltage Voc. That can be ascribed to the better passivation by thicker intrinsic a-Si:H. The dark current–voltage data reveal that the reverse leakage current and the diode ideality factor at high forward bias decrease monotonically with increasing the thickness of i-layer. Moreover, for the first time, we observe that the lower Voc is associated with the capacitance–voltage (C–V) curve shifting toward higher positive voltage. We propose that the shift of the curve is related to the capacitance affected by the surface states. Finally we prove that the improvement in the NW solar cell performance, especially the Voc, can be attributed to the reduction of the surface states on SiNWs.