Efficient a-Si:H(p) Buffer Layer to Improve the Interface Contact Performance of nc-Si:H(p)/ITO for High-Efficiency Silicon Heterojunction Solar Cell

Hydrogenated nanocrystalline silicon (nc-Si:H) is usually utilized to prepare carrier-selective contacts for silicon heterojunction (SHJ) solar cells to mitigate the negative parasitic optical absorption. Nevertheless, it was found here that for the SHJ solar cell based on an n-type crystalline silicon (c-Si(n)) wafer with the p-type boron-doped nc-Si:H(p) as the emitter, the solar cell fill factor (FF) was limited by the contact performance of the nc-Si:H(p)/indium tin oxide (ITO) interface due to the induced disorder defects in the interface vicinity regions by the lattice mismatch between the nc-Si:H(p) and ITO crystallites. A strategy to improve the nc-Si:H(p)/ITO contact was proposed by inserting an ultrathin (∼2 nm) p-type hydrogenated amorphous silicon (a-Si:H(p)) buffer layer (pb) onto the nc-Si:H(p)/ITO interface. The inserted amorphous buffer plays well to facilitate the relaxation of the lattice mismatch stress on the interface and thus avoids the generation of disorder defects. Its Fermi energy level (Ef), lower than that of nc-Si:H(p), also promotes the carrier tunneling with ITO. Further, the hydrogen dilution ratio (RH), boron doping (RB2H6), and thickness of the pb layer were optimized. Comparing to the solar cell without the pb layer, the FF and conversion efficiency of the solar cell with the optimized pb layer achieved a relative increase of 0.37% and 0.56%, respectively. Since crystalline/crystalline heterojunctions like the nc-Si:H(p)/ITO scheme are utilized in a variety of photonic devices, such an interface modification strategy of inserting an amorphous buffer can be of great importance in the photonics field.