In Situ Printing: Insights into the Morphology Formation and Optical Property Evolution of Slot‐Die‐Coated Active Layers Containing Low Bandgap Polymer Donor and Nonfullerene Small Molecule Acceptor

Abstract

Printing of active layers for high‐efficiency organic solar cells with the slot‐die coating technique can overcome the challenge of upscaling, which will be needed for organic photovoltaics on its way to marketability. The morphology of a bulk‐heterojunction organic solar cell has a very high impact on its power conversion efficiency. Therefore, it is of particular importance to understand the mechanisms of structure formation during printing of active layers to enable further optimization of the solar cell performance and upscaling of the production process. Meniscus‐guided slot‐die coating of the blend of a low bandgap conjugated polymer donor with benzodithiophene units PBDB‐T‐SF and the nonfullerene small molecule acceptor IT‐4F is studied in situ with optical microscopy, Ultraviolet–visible spectroscopy, and grazing incidence small angle X‐ray scattering. The structure formation is followed from the liquid to the final dry film state. Thereby, five regimes of morphology formation are determined. The morphological evolution in the printed active layer is correlated to changing optical properties of the thin film. In the final dry film, polymer domains of several tens of nanometers are observed, which will be favorable for application in high‐efficiency organic solar cells.

Following In Situ the Evolution of Morphology and Optical Properties during Printing of Thin Films for Application in Non-Fullerene Acceptor Based Organic Solar Cells

“…With respect to the very similar system PBDB-T-SF:IT-4F, basically the same film formation regimes were observed as for PBDB-T-2Cl:IT-4F . In both studies, the active material was slot-die-coated out of CB.…”

“…In an earlier work, we studied the in situ printing of poly­[(2,6-(4,8-bis­(5-(2-ethylhexylthio)-4-fluorothiophen-2-yl)­benzo­[1,2- b :4,5- b ′]­dithiophene))- alt -(5,5-(1′,3′-di-2-thienyl-5′,7′-bis­(2-ethylhexyl)­benzo­[1′,2′- c :4′,5′- c ′]­dithiophene-4,8-dione)], denoted PBDB-T-SF, blended with IT-4F from CB. Compared to PBDB-T-2Cl studied here, PBDB-T-SF showed in particular different energy levels.…”

Revealing Donor–Acceptor Interaction on the Printed Active Layer Morphology and the Formation Kinetics for Nonfullerene Organic Solar Cells at Ambient Conditions

“…Subsequently, these solutions were printed at ambient conditions on cleaned silicon substrates with a print speed of 5 mm s −1 and a flow rate of 0.1 mL min −1 using a custom-made slot-die coater. [48] A print head distance of 150 μm was installed to realize films with a thickness between 80 and 90 nm. Neat PDTBT2T-FTBDT and BTP-F4 films were prepared under identical conditions by using the initial CF or CB solutions.…”

In Situ Studies of Solvent Additive Effects on the Morphology Development during Printing of Bulk Heterojunction Films for Organic Solar Cells

“…In previous work, the printing process of BHJ films was described as five stages based on the growth rate of the polymer domains. [7,42] For example, in the case of the model system poly(3-hexylthiophene-2,5-diyl) (P3HT): [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM), which does not need additives, the influence of the substrate temperature was highlighted. [7] In contrast, in our work we address the effects of solvent additives on the morphology evolution of PPDT2FBT:PC 71 BM thin films during printing.…”