Improved power conversion efficiency of silicon nanowire solar cells based on transition metal oxides

An n-type Si nanowire (SiNW) solar cell based on transition metal oxides V2O5 and TiO2 has been fabricated. The cell is demonstrated in the ITO/V2O5/n-SiNWs/TiO2/Al heterojunction structure, in which the V2O5 and TiO2 work as the hole- and the electron-selective layers, respectively. Parameters of cells with different lengths of nanowires have been investigated. Owing to the excellent light trapping effect of nanowire arrays and superior carrier transporting properties of thin V2O5 and TiO2 layers, an improved power conversion efficiency of 12.7% has been achieved in a cell with 1.45-pm-long nanowires. Due to the large work function difference between V2O5 and n-Si, a build-in potential of 0.75 V was obtained from the capacitance-voltage measurement, which implies the possibility of achieving a large open circuit voltage for these nanowire solar cells. The efficiency loss is mainly caused by the recombination via the defects on the unpassivated surface of SiNWs. By solving this problem, the cell efficiency may be improved further and realize the application in PV industries.