Flexible PTB7:PC sub(71)BM bulk heterojunction solar cells with a LiF buffer layer

• Published in: Japanese Journal of Applied Physics 2014-01, Vol.53 (2S), p.02BE05-1-02BE05-5
• Main Authors: Yanagidate, Tatsuki, Fujii, Shunjiro, Ohzeki, Masaya, Yanagi, Yuichiro, Arai, Yuki, Okukawa, Takanori, Yoshida, Akira, Kataura, Hiromichi, Nishioka, Yasushiro
• Format: Article
• Language: English
• Subjects: Aluminum; Buffer layers; Devices; Electric potential; Heterojunctions; Indium tin oxide; Photovoltaic cells; Solar cells; Sulfonates
• ISSN: 0021-4922; 1347-4065
• DOI: 10.7567/JJAP.53.02BE05

Bulk heterojunction solar cells were fabricated using 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) and [6,6]-phenyl C sub(71) butyric acid methyl ester (PC sub(71)BM) after a layer of poly(3,4- ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was deposited on a flexible indium tin oxide (ITO)-coated polyethylene terephthalate substrate. The fabricated structures were Al/LiF/PTB7:PC sub(71)BM/PEDOT:PSS/ITO with or without a lithium fluoride (LiF) buffer layer, and the effect of the LiF buffer layer on the performance of the solar cells was investigated. The LiF layer significantly increased the opencircuit voltages and fill factors of the solar cells, presumably because of the work function shift of the aluminum cathode. As a result, the conversion efficiency increased from 2.31 to 4.02% owing to the presence of the LiF layer. From the results of a stability test, it was concluded that the inserted LiF layer acted as a shielding and scavenging protector, which prevented the intrusion of some chemical species into the active layer, thereby improving the lifetime of the unpakcaged devices.