Rapid thermal technologies for high-efficiency silicon solar cells

This paper shows that rapidly formed emitters in less than 6 min in the hot zone of a conveyor belt furnace or in 3 min in an rapid thermal processing (RTP) system, in conjunction with a screen-printed (SP) RTP Al-BSF and passivating oxide formed simultaneously in 2 min can produce very simple high-efficiency n+-p-p+ cells with no surface texturing, point contacts, or selective emitter. It is shown for the first time that an 80 Ω/□ emitter and SP Al-back surface field (BSF) formed in a high throughput belt furnace produced 19% FZ cells and greater than 17% CZ cells with photolithography (PL) contacts. Using PL contacts, we also achieved 19% efficient cells on FZ, >18% on MCZ, and ∼17% boron-doped CZ by emitter and SP Al-BSF formation in <10 min in a single wafer RTP system. Finally, manufacturable cells with 45 Ω/□ emitter and SP Al-BSF and Ag contacts formed in the conveyor belt furnace gave 17% efficient cells on FZ silicon. Compared to the PL cells, the SP cell gave ∼2% lower efficiency along with a decrease in Jsc and fill factor. This loss in performance is attributed to a combination of the poor blue response, higher series resistance and higher contact shading in the SP devices