Enhanced dichroic ratio of polymer semiconductor thin films aligned and oriented on nano-structured substrates
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We investigate how nano-structures of substrates affect orientation of cyclopentadithiophene–co–pyridylthiadiazole-based polymer semiconductor (PCDTPT) thin films. By spin casting PCDTPT solutions prepared with chloroform:1-chloronaphthalene (CF:1-CN) co-solvent on nano-grooved silicon dioxide substrates, we prepared unidirectionally aligned and oriented PCDTPT thin films with dichroic ratio as high as 3. This value is apparently higher than those of isotropic PCDTPT thin films spin cast from a PCDTPT solution based on single solvent (i.e., CF). We attribute the enhanced dichroic ratio of PCDTPT thin films to unidirectional alignment and orientation of polymer chains in the direction parallel to the nano-grooves on the substrate. Considering the complexity of the current orientation techniques for polymer semiconductors, our results provide a facile strategy for developing highly oriented polymer semiconductors used for optoelectronic devices such as polarimetric photodetectors.