High-Flux Solar Furnace Processing of Silicon Solar Cells

We used a 10-kW, high-flux solar furnace (HFSF) to diffuse the front-surface n+-p junction and the back-surface p-p+ junction of single-crystal silicon solar cells in one processing step. We found that all of these HFSF-processed cells have better conversion efficiencies than control cells of identical structures fabricated by conventional furnace diffusion methods. We also used the HFSF tocrystallize a-Si:H thin films on glass, to texture crystalline silicon surfaces, to deposit gold contacts on silicon wafers, and to getter impurities from metallurgical grade silicon. HFSF processing offers several advantages over conventional furnace processing: (1) it provides a cold-wall process, which reduces contamination; (2) temperature versus time profiles can be precisely controlled;(3) wavelength, intensity, and spatial distribution of the incident solar flux can be controlled and changed rapidly; (4) a number of high-temperature processing steps can be performed simultaneously; and (5) combined quantum and thermal effects may benefit overall cell performance. We conclude that HFSF processing of silicon solar cells has the potential to improve cell efficiency, reduce cellfabrication costs, and also be an environmentally friendly manufacturing method. We have also demonstrated that the HFSF can be used to achieve solid-phase crystallization of a-Si:H at very high speed.