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We investigated the effect of the B2H6 plasma treatment on p-type hydrogenated amorphous silicon (p-a-Si:H) surfaces for high-performance silicon heterojunction (SHJ) solar cells. Secondary ion mass spectroscopy measurements revealed that the boron concentration at the p-a-Si:H surface is increased by employing the B2H6 plasma treatment. Furthermore, specific contact resistance is decreased by about one-third after the B2H6 plasma treatment. No degradation of passivation performance is induced by the B2H6 plasma treatment. The power conversion efficiency of the SHJ solar cells with the B2H6 plasma treatment 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 B2H6 plasma treatment, which is responsible for the improved FF owing to facilitated tunneling holes from c-Si to p-a-Si:H layers and the TCO/p-a-Si:H heterointerface.

The theoretical lateral current of the surface inversion layer in a crystalline silicon (cSi) surface for a p-aSi:H/i-aSi:H/cSi heterojunction (SHJ) solar cell was calculated using computer simulation and was compared with the experimental one to study defects/traps at the aSi:H/cSi interface and/or in the cSi surface and to detect the acceptor concentration (N a) in p-aSi:H. To experimentally extract the lateral surface inversion layer current, a field-effect transistor type test element group device was co-integrated with SHJ cells on the same wafer. From the correlation between the experimental and calculated lateral surface inversion layer current, the density of defects/traps (D it) at the aSi:H/cSi interface and/or in the cSi surface and the value of N a were extracted. The calculated lateral surface inversion layer current stayed unchanged for various minority carrier lifetimes in the substrate, suggesting that this method is not suffered from the variation in the material parameters in the substrate.