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 a-SiO_X:B), 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 SiO₂ phase by FTIR and BRL. The a-SiO_X:B layer is deposited by PECVD using SiH₄, B₂H₆, H₂, CO₂ gases in N-type wafer and annealed by thermal tube furnace for performing the P+ layer. MCLT (minority carrier lifetime) is improved by increasing SiH₄ and B₂H₆. When a-SiO_X:B 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.

Crystalline silicon solar cells with SiNx/SiNx and SiNx/SiOx double layer anti-reflection coatings(ARC) were studied in this paper. Optimizing passivation effect and optical properties of SiNx and SiOx layer deposited by PECVD was performed prior to double layer application. When the refractive index (n) of silicon nitride was varied in range of 1.9∼2.3, silicon wafer deposited with silicon nitride layer of 80 nm thickness and n= 2.2 showed the effective lifetime of 1,370 ㎛. Silicon nitride with n= 1.9 had the smallest extinction coefficient among these conditions. Silicon oxide layer with 110 nm thickness and n= 1.46 showed the extinction coefficient spectrum near to zero in the 300∼1,100 nm region, similar to silicon nitride with n= 1.9. Thus silicon nitride with n= 1.9 and silicon oxide with n= 1.46 would be proper as the upper ARC layer with low extinction coefficient, and silicon nitride with n=2.2 as the lower layer with good passivation effect. As a result, the double layer AR coated silicon wafer showed lower surface reflection and so more light absorption, compared with SiNx single layer. With the completed solar cell with SiNx/SiNx of n= 2.2/1.9 and SiNx/SiOx of n= 2.2/1.46, the electrical characteristics was improved as ΔVoc= 3.7 mV, ΔJsc= 0.11 mA/cm2 and Δ Voc= 5.2 mV, ΔJsc= 0.23 mA/cm2, respectively. It led to the efficiency improvement as 0.1% and 0.23%.

Limiting thermal exposure time using rapid thermal processing(RTP) has emerged as promising simplified process for manufacturing of solar cell in a continuous way. This paper reports the simplification of co-firing using RTP. Actual temperature profile for co-firing after screen printing is a key issue for high-quality metal-semiconductor contact. The plateau time during the firing process were varied at 450℃ for 10~16 sec. Glass frit in Ag paste etch anti-reflection layer with plateau time. Glass frit in Ag paste is important for the Ag/Si contact formation and performances of crystalline Si solar cell. We achieved 17.14% efficiency with optimum conditions.