Solution processing via roll-to-roll (R2R) coating promises a low cost, low thermal budget, sustainable revolution for the production of solar cells. Poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′′′-di(2-octyldodecyl)-2,2′;5′,2′′;5′′,2′′′-quaterthiophen-5,5-diyl)], PffBT4T-2OD, has recently been shown to achieve high power conversion efficiency (>10%) paired with multiple acceptors when thick films are spun-coat from hot solutions. We present detailed morphology studies of PffBT4T-2OD based bulk heterojunction films deposited by the volume manufacturing compatible techniques of blade-coating and slot-die coating. Significant aspects of the film morphology, the average crystal domain orientation and the distribution of the characteristic phase separation length scales, are remarkably different when deposited by the scalable techniques vs. spun-coat. Yet, we find that optimized blade-coated devices achieve PCE > 9.5%, nearly the same as spun-coat. These results challenge some widely accepted propositions regarding what is an optimal BHJ morphology and suggest the hypothesis that diversity in the morphology that supports high performance may be a characteristic of manufacturable systems, those that maintain performance when coated thicker than ≈200 nm. In situ measurements reveal the key differences in the solidification routes for spin- and blade-coating leading to the distinct film structures. © 2016 The Royal Society of Chemistry.
KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: J. D. acknowledges support of a NIST-NRC postdoctoral fellowship. H. W. R. acknowledges support from the U.S. Department of Commerce, National Institute of Standards and Technology under financial assistance awards 70NANB15H079. X-ray characterization and analysis by NCSU was supported by the U.S. Department of Energy, Office of Science, Basic Energy Science, Division of Materials Science and Engineering under Contract DE-FG02-98ER45737. X-ray data was acquired at beamlines 7.3.3 and 22.214.171.124 at the Advanced Light Source, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. E. Schaible, C. Zhu, A. Hexemer, C. Wang, and A. Young of the ALS (DOE) assisted with the measurements and provided instrument maintenance.