Inverted Organic Solar Cells Based on PTB7:PC71BM with PFN Electron Transport Layer on ITO-Free Flexible PEN Substrate

Wednesday, October 14, 2015: 11:20
Ellis West (Hyatt Regency)
K. Hashiba, R. Nagata (College of Science and Technology, Nihon University), K. Kiriishi (College of Science and Technology, Nihon University), H. Kataura (Nat. Inst. of Advanced Industrial Science and Technology), S. Fujii (Nat. Inst. of Advanced Industrial Science and Technology), and Y. Nishioka (College of Science and Technology, Nihon University)
Polyfluorene: poly(9,9,-bis(3'-(N,N-dimethyl)-propyl-2,7-fluorene)alt- 2,7-(9,9-dioctylfluorene)) (PFN) has been recently reported as a good electron transport layer for organic bulk-heterojunction (BHJ) solar cells by Chang et al. [1]. They fabricated BHJ solar cells based on [4,8-biz[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 phenyl-C71-butyric-acid-methyl-ester (PC71BM) on indium tin oxide (ITO) glass substrates with PFN as an electron transport layer, and it showed the efficiency as high as 9.2%.

In this paper, we report on the improved long term reliability of similar solar cells with an ITO-free flexibleinverted solar cell structures of PEN/PEDOT:PSS/PFN/(PTB7:PC71BM)/MoO3/Au using, and found these devices showed much improved long-term reliability of the devices stored in air without any surface passivation layer. The J-C characteristics showed a slight reduction in the short cuircuit current density after storage in air for 4 days. The use of the PFN layer also significantly enhanced not only the open-circuit voltages and the power conversion efficiencies of the solar cells presumably due to the high electron transport efficiency and the better contact between the PEDOT:PSS cathode and the PTB7:PC71BM active layer. Although the resulted conversion efficiency was only 1.8% at this moment, and further process improvement will be continued.Furthmore we tried efficiency of the device change in the PFN thickness by spin-coating time.

[1] Yi-Ming Chang, and Chi-Yi Leu. Journal of Materials Chemistry A 1.21 (2013): 6446-6451.