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

Published

June 2, 2020

Author(s)

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

Abstract

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.

Citation

ACS Applied Materials and Interfaces

Volume

12

Pub Type

Journals

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DOI Link

Keywords

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

Citation

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], https://doi.org/10.1021/acsami.0c04108 (Accessed April 25, 2024)