PTB7:PC71BM Bulk Heterojunction Solar Cells with Multiple Additives

Wednesday, October 14, 2015: 09:00
Ellis West (Hyatt Regency)
M. Ohzeki (College of Science and Technology, Nihon University), J. Qiu (College of Science and Technology, Nihon University), S. Fujii (Nat. Inst. of Advanced Industrial Science and Technology), H. Kataura (Nat. Inst. of Advanced Industrial Science and Technology), and Y. Nishioka (College of Science and Technology, Nihon University)
Bulk-hetero junction organic solar cells with active layers 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] and phenyl-C71-butyric-acid-methyl-ester (PC71BM) with an additive of diiodooctane (DIO) has attracted a lot of attentions due to their high power conversion efficiencies over 9% [1]. The addition of DIO significantly improved the solar cell performance, which was considered due to the change of the nano-structure configulations by the introduction of DIO. On the other hand,  the introduction of dimethyl sulfoxide (DMSO) into the dicholobenzen solution of PTB7:PC71BM used to deposit the active layers [2]. However, the influence of the DMSO introduction into the PTB7:PC71BM:DIO systems have not yet been reported to the best of our knowledge.

In this work, active layers were fabricated by spin coating 1,2-dichlorobenzene (500 μl) solutions of PTB7 (5 mg): PC71BM (7.5 mg) containing 0.369 mg (3wt%) of DIO and additional DMSO with different weight ratios to the total weight of PTB7:PC71BM (12.5 mg) from 0 to 30 wt% (0 to 3.69 mg).  It was found that the solar cells with 13wt% (1.60 mg) of DMSO additives exhibited the best solar cell performance of an open circuit voltage of 0.72 V, short circuit current density of 15.63 mA/cm2, fill factor of 0.49, and power conversion efficiency of 5.47%. The significant structural changes were found from the surface morphology observations of the active layers depending on the DMSO concentration as observed by atomic force microscope.

[1] Z. He et al., Nat Photonics 6, (2012) 591.

[2] Chu et al., Appl. Phys. Lett. 98, (2011) 253301.