Organic Solar Cells Based on PTB7:PC71BM with Cs2CO3 as a Cathode Buffer Layer

• Published in: Journal of Photopolymer Science and Technology 2014/07/08, Vol.27(5), pp.577-581
• Main Authors: Kaneto, Daichi, Yanagidate, Tatsuki, Yanagi, Yuichiro, Fujii, Shunjiro, Kataura, Hiromichi, Nishioka, Yasushiro
• Format: Article
• Language: English
• Subjects: bulk heterojunction; cesium carbonate; PC71BM; PTB7; solar cell
• ISSN: 0914-9244; 1349-6336
• DOI: 10.2494/photopolymer.27.577

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 C71 butyric acid methyl ester (PC71BM) after a layer of poly(3,4- ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was deposited on an indium tin oxide (ITO)-coated glass substrate. The fabricated structures were glass/ITO/PEDOT:PSS/PTB7:PC71BM/Cs2CO3/Al with or without the cesium carbonate (Cs2CO3) buffer layer, and the effect of the buffer layer on the performance of the solar cells was investigated. The Cs2CO3 layer with a thickness of 0.8 nm significantly increased the short circuit current density, open-circuit voltages and fill factors of the solar cells, presumably because of the better contact between the active layer and the cathode and the work function shift of the aluminum cathode. As a result, the power conversion efficiency increased from 1.09 to 2.12%. However, when thickness of the Cs2CO3 exceeded 2 nm, significant degradation was observed. From the results of a stability test, it was suggested that the inserted Cs2CO3 layer had a minimal influence on the lifetime of the unpakcaged devices.