Gapless point back surface field for the counter doping of large‐area interdigitated back contact solar cells using a blanket shadow mask implantation process

• Published in: Progress in photovoltaics 2017-12, Vol.25 (12), p.989-995
• Main Authors: Kim, Young‐Su, Mo, Chanbin, Lee, Doo Youl, Park, Sung Chan, Kim, Dongseop, Nam, Junggyu, Yang, JungYup, Suh, Dongchul, Kim, Hyun‐Jong, Park, Hyomin, Park, Se Jin, Kim, Donghwan, Song, Jungho, Lee, Hae‐Seok, Park, Sungeun, Kang, Yoonmook
• Format: Article
• Language: English
• Subjects: Boron; Cadmium telluride; Contact resistance; counter doping; Doping; Emitters; Energy conversion efficiency; gapless doping; IBC solar cells; Ion implantation; Phosphorus; Photovoltaic cells; Shunt resistance; Solar cells
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.2910

Gapless interdigitated back contact (IBC) solar cells were fabricated with phosphorous back surface field on a boron emitter, using an ion implantation process. Boron emitter (boron ion implantation) is counter doped by the phosphorus back surface field (BSF) (phosphorus ion implantation) without gap. The gapless process step between the emitter and BSF was compared to existing IBC solar cell with gaps between emitters and BSFs obtained using diffusion processes. We optimized the doping process in the phosphorous BSF and boron emitter region, and the implied Voc and contact resistance relationship of the phosphorous and boron implantation dose in the counter doped region was analyzed. We confirmed the shunt resistance of the gapless IBC solar cells and the possibility of shunt behavior in gapless IBC solar cells. The highly doped counter doped BSF led to a controlled junction breakdown at high reverse bias voltages of around 7.5 V. After the doping region was optimized with the counter doped BSF and emitter, a large‐area (5 inch pseudo square) gapless IBC solar cell with a power conversion efficiency of 22.9% was made. A cost effective gapless IBC was fabricated by using ion implantation with shadow masks. We fabricated IBC solar cell with optimized doping condition at counter doped region. The shunt resistance and junction breakdown confirmed that the shunt resistance was over 5000 Ω cm2 in the case of the average shunt resistance value. After the doping conditions were optimized, a high efficiency of 23% was achieved with a fill factor of over 81%.