N-type 고효율 태양전지용 Boron Diffused Layer의 형성 방법 및 특성 분석

Abstract

N-type crystalline silicon solar cells have high metal impurity tolerance and higher minority carrier lifetime that increases conversion efficiency. However, junction quality between the boron diffused layer and the n-type substrate is more important for increased efficiency. In this paper, the current status and prospects for boron diffused layers in N-type crystalline silicon solar cell applications are described. Boron diffused layer formation methods (thermal diffusion and co-diffusion using <TEX>$a-SiO_X:B$</TEX>), boron rich layer (BRL) and boron silicate glass (BSG) reactions, and analysis of the effects to improve junction characteristics are discussed. In-situ oxidation is performed to remove the boron rich layer. The oxidation process after diffusion shows a lower B-O peak than before the Oxidation process was changed into <TEX>$SiO_2$</TEX> phase by FTIR and BRL. The <TEX>$a-SiO_X:B$</TEX> layer is deposited by PECVD using <TEX>$SiH_4$</TEX>, <TEX>$B_2H_6$</TEX>, <TEX>$H_2$</TEX>, <TEX>$CO_2$</TEX> gases in N-type wafer and annealed by thermal tube furnace for performing the P+ layer. MCLT (minority carrier lifetime) is improved by increasing <TEX>$SiH_4$</TEX> and <TEX>$B_2H_6$</TEX>. When <TEX>$a-SiO_X:B$</TEX> is removed, the Si-O peak decreases and the B-H peak declines a little, but MCLT is improved by hydrogen passivated inactive boron atoms. In this paper, we focused on the boron emitter for N-type crystalline solar cells.