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Co-solvent effects when blade coating a low-solubility conjugated polymer for bulk-heterojunction organic photovoltaics



Lee J. Richter, Ian Pelse, Jeff Hernandez, Sebastian Engmann, Andrew Herzing, John R. Reynolds


The adoption of solution processed active layers in the production of thin-film photovoltaics is hampered by the transition from research fabrication techniques to scalable processing. We report a detailed study of the role of processing in determining the morphology and performance of organic photovoltaic devices using a commercially available, low solubility, and high molecular mass diketopyrrolopyrrole based polymer donor. Ambient blade-coating of thick layers in an inverted architecture was performed to best model scalable processing. Device performance is strongly dependent on the introduction of either o-dichlorobenzene (DCB), 1,8-diiodooctane (DIO), or diphenyl ether (DPE) cosolvent into the chloroform (CHCl3) solution, which are all shown to drastically improve the morphology. To understand the origin of these morphological changes as a result of the addition of the co-solvent, in-situ processing characterization methods were used to characterize the morphology that evolves during coating and solidification. When comparing the CHCl3 + DCB cast films to the CHCl3 only cast films in depth with in-situ grazing incidence x-ray scattering and optical reflection interferometry, we identify a decrease in domain size and increase in crystallinity that occurs during the evaporation of DCB. We find that all three co-solvents likely plasticize the film leading to reduced domain size and increased polymer crystallinity in films relative to those cast from chloroform alone. This results in percolated bulk-heterojunction networks that perform similarly well with a wide range of film thicknesses from 180 nm to 440 nm, making this system amenable to continuous roll-to-roll processing methods.
ACS Applied Materials and Interfaces


photovoltaics, polymer, bulk heterojunction, X-ray, hyperspectral


Richter, L. , Pelse, I. , Hernandez, J. , Engmann, S. , Herzing, A. and Reynolds, J. (2020), Co-solvent effects when blade coating a low-solubility conjugated polymer for bulk-heterojunction organic photovoltaics, ACS Applied Materials and Interfaces, [online], (Accessed May 17, 2024)


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Created June 2, 2020, Updated April 11, 2023