Enhanced device performance of Si nanowires/Si nanocrystals heterojunction solar cells with ultrathin Al2O3 passivation

Silicon nanowires (Si NWs) can be used to fabricate silicon nanocrystals (Si NCs)/Si heterojunction solar cells because of their excellent antireflection and superior absorption properties. The reflection of the Si NWs prepared via metal-assisted chemical etching is dramatically reduced over a wide spectral range from 300 to 1200 nm. However, the etched Si NWs contain a large amount of surface defect states, which deteriorate the device performance due to the serious surface recommbination loss. After inserting Al2O3 layer as passivation layer between Si NWs and Si NCs, the performance of device is greatly improved. The external quantum efficiency (EQE) is obviously enhanced over the whole measurement spectral range, which increases the short circuit currenty density (Jsc) from 25.65 mA/cm2 to 30.89 mA/cm2. As a consequence, the power conversion efficiency (PCE) of the optimized device can reach as high as 9.36%.