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

In 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.