Field-Induced Radial Junction for Dopant-Free Crystalline Silicon Solar Cells with an Efficiency of over 20%

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 an 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 the 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 exhibit 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.