The power conversion efficiency (PCE) of small-molecule bulk heterojunction solar cells is highly sensitive to the “ink” formulation used to produce the photoactive layer. Here we demonstrate that the addition of nucleating agents renders device fabrication notably less susceptible to the ink composition, promising a route toward more robust processing of efficient devices over large areas and enabling more facile materials screening. We selected as a model system blends of 7,7-[4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b]dithiophene-2,6-diyl]bis[6-fluoro-4-(5-hexyl-[2,2-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole](p-DTS(FBTTh2)2) as the donor and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as the acceptor because this is one of the small-molecule OPV blends with a device performance that is most sensitive to ink formulation, especially when used with the processing aid diiodooctane (DIO). Addition of DIO is essential to obtain high device performances; however, a notable increase in device performance is only achieved over a very narrow DIO content regime. Use of nucleating agents drastically changes this situation and leads to well-performing devices even at extreme levels of DIO. We thus start to address here one of the great challenges in organic solar cell research: the fact that, too often, only a very limited composition range leads to high efficiency devices. This means that for every new donor or acceptor a multitude of formulations have to be tested, including in combination with processing aids, to ensure that promising materials are not overlooked. The use of nucleating agents, thus, promises to render materials discovery more straightforward as this dependency of device performance with composition can be reduced.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): CRG-1-2012-THO-015
Acknowledgements: We are grateful for fruitful discussions with Dean M. DeLongchamp, Lee J. Richter, David J. Gundlach, Maged Abdelsamie, and Aram Amassian, all of which have been invaluable for the construction of this manuscript. N.D.T. acknowledges support from the National Science Foundation’s International Research Fellowship Program (OISE-1201915) and the European Research Council’s Marie Curie International Incoming Fellowship under Grant Agreement No. 300091. N.S. is grateful for support by a European Research Council Starting Independent Researcher Fellowship under Grant Agreement No. 279587 and funding by King Abdullah University of Science and Technology (KAUST CRG: CRG-1-2012-THO-015). The time-resolved microwave photoconductivity experiments described here were funded by the Solar Photochemistry Program, Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy under Contract No. DE-AC36-08-GO28308 with the National Renewable Energy Laboratory. The UCSB MRL Shared Experimental Facilities are supported by the MRSEC Program of the NSF under Award No. DMR 1720256, a member of the NSF-funded Materials Research Facilities Network; work at UCSB was supported by NSF DMR 1436263. The authors declare no competing financial interest.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.