Performance improvement of flexible bulk heterojunction solar cells using PTB7:PC 71 BM by optimizing spin coating and drying processes

• Published in: Japanese Journal of Applied Physics 2014-02, Vol.53 (2S), p.2
• Main Authors: Ohzeki, Masaya, Fujii, Shunjiro, Arai, Yuki, Yanagidate, Tatsuki, Yanagi, Yuichiro, Okukawa, Takanori, Yoshida, Akira, Kataura, Hiromichi, Nishioka, Yasushiro
• Format: Article
• Language: English
• ISSN: 0021-4922; 1347-4065
• DOI: 10.7567/JJAP.53.02BE04

Bulk-heterojunction solar cells were fabricated using a dichlorobenzene solution of poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2- b :4,5- b ′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4- b ]-thiophenediyl] (PTB7):[6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) on a flexible indium–tin-oxide-coated polyethylene terephthalate substrate. It was found that the performance of the solar cells could be markedly improved by minimizing the spin coating time of a blend of PTB7 and PC 71 BM to 10 s and maximizing the successive drying and solidification time up to 30 min in a confined Petri dish. As a result, a short-circuit current density of 14.5 mA/cm 2 , an open-circuit voltage of 0.62 V, and a power conversion efficiency of 3.67% were obtained. These improvements are attributed to the growth of favorable nanostructures during the slow drying process that increased the photocarrier collection efficiency while simultaneously increasing the performance fluctuations of each device.