CO-DIFFUSION FOR P-TYPE PERT SOLAR CELLS USING APCVD BSG LAYERS AS BORON DOPING SOURCE

摘要

In this work, we investigate boron-doped back surface field (BSF) formation from borosilicate glass (BSG) deposited by atmospheric pressure chemical vapor deposition (APCVD). Carrier lifetime samples with different boron concentration in the BSG are exposed to high-temperature processes with varying temperature and gas atmospheres. The development aims at producing p-type Si-based passivated emitter and rear totally diffused (PERT) cells in a POCl_3 co-diffusion process. Our experiments confirm the critical impact of the O_2 concentration on boron diffusion from APCVD BSG layers. For different peak temperatures Si surface oxidation formation need to be balanced carefully. Moderate diffusion temperatures of 875°C (30 min) yield a BSF doping with R_(sh) = 131 Ω/sq and a recombination current density of J_(0, BSF) = 21 fA/cm~2 (planar surface, AlO_x/SiN_x-passivation). Finally, 156 mm sized PERT cells fabricated from p-type Czochralski-grown Si wafers using the developed co-diffusion process show peak efficiencies of 20.6%, confirming the feasibility of our co-diffusion approach.