Despite having surpassed 10% power conversion efficiency (PCE), widely held as the threshold for commercial viability, high performance organic photovoltaics (OPVs) are still mostly constrained to lab-scale devices fabricated by spin coating. Efforts to produce scalable continuously printed OPVs trail significantly in efficiency, highlighting the need to better understand the processing-morphology-performance relationship in the context of linear printing processes. Here we investigate the promising OPV system PTB7-Th/PC71BM, which has demonstrated &gt;10% PCE via spincoating but only exhibits ~1% PCE when roll-to-roll printed due to differences in drying dynamics. Of particular interest is the ubiquitous alcohol post-treatment wash applied to the active layer and its crucial role for printed films. Although it is commonly believed to simply remove the processing additive, 1,8-diiodooctane (DIO), from the dried film, we find that the wash process itself dramatically impacts film morphology and performance. By employing hard and soft x-ray characterization techniques we determine that isopropanol induces significant donor polymer alignment, enhanced relative degree of crystallinity, and increased domain purity. Through the understanding gained in this study, we are able to achieve a roll-to-roll printed OPV exceeding 6% PCE (5.1% avg), which is to our knowledge the highest reported performance for a continuous roll-to-roll printed single junction photoactive layer on a flexible substrate.

High performance roll-to-roll printed PTB7-Th/PC71BM organic solar cells

256th National Meeting (2018)

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