Effect of asymmetric solubility of diketopyrrolopyrrole-based polymers and PC71BMs in a binary solvent system on the performance of bulk heterojunction solar cells

• Published in: Solar energy materials and solar cells Vol. 124; pp. 232 - 240
• Main Authors: Son, Seon Kyoung, Lee, Hyo-Sang, Ha, Jae Seung, Kim, Kyung Hwan, Son, Hae Jung, Ko, Min Jae, Kim, Honggon, Lee, Doh-Kwon, Kim, Jin Young, Lee, Wonmok, Park, Sungnam, Choi, Dong Hoon, Kim, BongSoo
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.05.2014; Elsevier
• Subjects: Applied sciences; Binary solvent system; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Energy; Exact sciences and technology; Hole mobility; Morphology; Natural energy; Organic photovoltaics; Photoelectric conversion; Photovoltaic conversion; Polymer solar cell; Power conversion efficiency; Solar cells. Photoelectrochemical cells; Solar energy; Binary solvent system; Organic photovoltaics; Polymer solar cell; Power conversion efficiency; Morphology; Hole mobility; Performance evaluation; Polymer blends; Fullerene compounds; Conversion rate; Binary system; Boiling point; Solubility; Polymer; Organic solar cells; Butyric acid; Photovoltaic cell; Solar cell; Ester; System performance; Energy conversion; Fullerenes; Comparative study; Heterojunction
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2014.02.011

In this study, we demonstrated the effective morphological control of polymer:fullerene blends using three separate solvent systems: chloroform (CF), CF:1,8-diiodooctane (DIO), and CF:o-dichlorobenzene (ODCB). The polymer:fullerene blends are composed of two diketopyrrolopyrrole (DPP)-based polymers of P(DPP-alt-QT) and P(DPP-alt-DTBSe) and a fullerene derivative of [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), i.e., P(DPP-alt-QT):PC71BM or P(DPP-alt-DTBSe):PC71BM. The CF:ODCB binary solvent exhibited the best photovoltaic performance among the three solvent systems for both polymer-based devices, although the CF:DIO also exhibited an improved performance compared to the CF system. By examining film morphology of the blend films, we found that the CF:ODCB enabled the most optimal nanoscale phase separation and the morphological features were strongly affected by the solubility of each material in the high boiling-point (BP) solvent. Specifically, the polymers have limited but slightly higher solubility in ODCB than in DIO, while the PC71BM molecules have a high solubility in both DIO and ODCB. Therefore, this work highlights that the optimally asymmetric solubility of each photoactive component in the high BP solvent is a critical factor to form the nanoscale, bicontinuous domains in the blend films and thereby to determine the performance of photovoltaic devices. [Display omitted] •We report the effective morphological control of polymer:fullerene blends.•We fabricated OPV devices using two polymers: P(DPP-alt-QT) and P(DPP-alt-DTBSe).•CF:o-dichlorobenzene enabled the most optimal nanoscale phase separation.•CF:o-dichlorobenzene solvent system gave the best photovoltaic performance.•Asymmetric solubility of each photoactive component in solvent was a key to control morphology.