Boron Delta-Doping in Hydrogenated Amorphous Silicon for High-Performance Silicon Heterojunction Solar Cells

We investigated the effect of the boron delta-doping process at p-type hydrogenated amorphous silicon (p-a-Si:H) surface for high-performance silicon heterojunction (SHJ) solar cells. Secondary ion mass spectroscopy measurements revealed that B concentration at the p-a-Si:H surface is increased by employing the B delta-doping process. Furthermore, specific contact resistance is decreased about one-third owing to the B delta-doping layer. No degradation of passivation performance is induced by the presence of the B delta-doping layer. The power conversion efficiency of the SHJ solar cells with the B delta-doping layer is improved by the increase in fill factor (FF) due to decreased series resistance and increased shunt resistance. From numerical simulations, the upward band bending is enhanced at the heterointerface between transparent conductive oxide (TCO) and p-a-Si:H by the B delta-doping, which is responsible for the improved FF owing to facilitated tunneling holes from c-Si to p-a-Si:H layers and TCO/p-a-Si:H heterointerface. The B delta-doping process can be readily adaptable in the fabrication procedures of conventional SHJ solar cells and improve TCO/p-a-Si:H contact properties without degradation in passivation performance.