Field-induced radial junction for dopant-free crystalline silicon solar cells with an efficiency of over 20%

Abstract

Radial junctions on crystalline silicon (c-Si) microwire structures considerably reduce the diffusion length of photo-induced minority carriers required for energy generation by decoupling light absorption and carrier separation in orthogonal spatial direction. Hence, radial junctions mitigate the need for high-purity materials, and thus reduce the fabrication cost of c-Si solar cells. In this study, the formation of dopant-free radial junctions from atomic layer deposition (ALD) of Al2O3 on an n-c-Si microwire surface is reported. ALD-Al2O3 generates a p+ inversion layer, which eventually forms the radial junction on the n-c-Si surface. The width of depletion region induced by the p+ inversion layer is calculated from PC1D simulation as 900 nm. The fabricated dopant-free radial junction c-Si solar cells exhibits a power conversion efficiency of 20.1%, which is higher than those of previously reported microwire-based radial junction solar cells. Notably, internal quantum efficiencies of over 90% were obtained in the 300–980 nm wavelength region, thereby verifying the successful formation of radial junctions.