Journal
ADVANCED ENERGY MATERIALS
Volume 10, Issue 34, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.202001589
Keywords
chlorination; crystallization; organic solar cells; phase separation; small molecular donors
Categories
Funding
- Netherlands Organisation for Scientific Research
- Ministry of Education, Culture and Science [024.001.035]
- Netherlands Organisation for Scientific Research [016.Veni.192.106]
- Marie Skodowska-Curie Actions Innovative Training Network [H2020-MSCAITN-2014 INFORM - 675867]
- ONR [N000141712204]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
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Compared to conjugated polymers, small-molecule organic semiconductors present negligible batch-to-batch variations, but presently provide comparatively low power conversion efficiencies (PCEs) in small-molecular organic solar cells (SM-OSCs), mainly due to suboptimal nanomorphology. Achieving precise control of the nanomorphology remains challenging. Here, two new small-molecular donorsH13andH14, created by fluorine and chlorine substitution of the original donor moleculeH11, are presented that exhibit a similar or higher degree of crystallinity/aggregation and improved open-circuit voltage with IDIC-4F as acceptor. Due to kinetic and thermodynamic reasons,H13-based blend films possess relatively unfavorable molecular packing and morphology. In contrast, annealedH14-based blends exhibit favorable characteristics, i.e., the highest degree of aggregation with the smallest paracrystalline pi-pi distortions and a nanomorphology with relatively pure domains, all of which enable generating and collecting charges more efficiently. As a result, blends withH13give a similar PCE (10.3%) as those made withH11(10.4%), while annealedH14-based SM-OSCs have a significantly higher PCE (12.1%). Presently this represents the highest efficiency for SM-OSCs using IDIC-4F as acceptor. The results demonstrate that precise control of phase separation can be achieved by fine-tuning the molecular structure and film formation conditions, improving PCE and providing guidance for morphology design.
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