A simplified and masking‐free doping process for interdigitated back contact solar cells using an atmospheric pressure chemical vapor deposition borosilicate glass / phosphosilicate glass layer stack for laser doping followed by a high temperature step

Abstract

AbstractIn this paper a simplified approach for the generation of laterally p‐ and n‐doped structures applicable for cost‐effective production of interdigitated back contact (IBC) solar cells is presented. We use a stack of doping glasses deposited by atmospheric pressure chemical vapor deposition (APCVD), consisting of borosilicate glass (BSG) and phosphosilicate glass (PSG) on Czochralski‐grown (Cz) silicon substrates. A laser process creates the p‐doped regions by local liquid phase diffusion of boron from the BSG layer into the underlying molten Cz‐Si substrate. Simultaneously, the BSG‐PSG stack is removed by laser ablation. In a subsequent high‐temperature step, phosphorus diffuses from the remaining PSG‐BSG layer into the crystalline silicon substrate under inert gas atmosphere, creating complementary to laser doped areas n+‐doped regions. By the use of APCVD, phosphorus and boron contents of the doping glasses can be adjusted freely to vary the resulting p‐ and n‐doped profiles. A higher boron content in the BSG layer enhances the diffusion of phosphorus through the BSG, especially at lower diffusion temperatures. The resulting doping profiles are characterized using electrochemical capacitance‐voltage measurements and the resulting sheet resistances using the four‐point probe method. The amount of minority dopant contamination in n‐ and p‐doped regions is investigated by secondary ion mass spectrometry. Furthermore, transfer length method (TLM)‐measurements indicate contactability of the generated doped regions.