Structural Study of Diketopyrrolopyrrole Derivative Thin Films: Influence of Deposition Method, Substrate Surface, and Aging

We report the morphology and microstructure of n-dialkyl side-chain-substituted thiophene DPP end-cappedwith phenylgroups (Ph-TDPP-Ph) thin films and compare the influence of depositionmethod and substrate surface using thermally oxidized Si and graphenesubstrates as well as monolayer graphene surfaces with an underlyingself-assembled octadecyltrichlorosilane monolayer, complemented byan aging study of spin-coated films over a 2 weeks aging period. Adistinct difference in morphology was observed between spin-coatedand vacuum-deposited thin films, which formed a fiber-like morphologyand a continuous layer of terraced grains, respectively. After aninitial film evolution, all combinations of deposition method andsubstrate type result in well-ordered thin films with almost identicalcrystalline phases with slight variations in crystallinity and mosaicity.These findings point toward strong intermolecular forces dominatingduring growth, and the templating effect observed for other oligomerfilms formed on graphene is consequently ineffective for this materialtype. Upon aging of spin-coated films, a noticeable evolution involvingtwo different morphologies and crystalline phases were observed. Afterseveral days, the thin film evolved into a more stable crystal phaseand a fiber-like morphology. Moreover, slight variation in opticalspectra were elucidated on the basis on density functional theorycalculations. These results demonstrate that thin-film propertiesof DPP derivatives can be tailored by manipulating the film formationprocess.

Automated summary

This study investigates the influence of deposition method and substrate surface on the morphology and microstructure of n-dialkyl side-chain-substituted thiophene DPP end-capped with phenyl groups (Ph-TDPP-Ph) thin films. Different morphologies were observed between spin-coated and vacuum-deposited thin films, with fiber-like morphology and continuous layer of terraced grains, respectively. After initial film evolution, all deposition methods and substrate types resulted in well-ordered thin films with slight variations in crystallinity and mosaicity. Aging of spin-coated films showed noticeable evolution in morphology and crystalline phases, indicating the possibility of tailoring the thin-film properties of DPP derivatives through film formation process manipulation.