Spontaneously Induced Hierarchical Structure by Surface Energy in Novel Conjugated Polymer‐Based Ultrafast‐Response Organic Photodetectors

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Abstract
A novel conjugated polymer, poly(4‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophen‐2‐yl)‐2,6‐dioctylbenzo[1,2‐d:4,5‐d']bis(oxazole)) (PBB), is synthesized for use in ultrafast‐response organic photodetectors (OPDs). The PBB synthesis is considered facile because a monomer could be isolated without column chromatography purification. The excellent solubility of PBB allows easy dissolution in both halogenated and nonhalogenated solvents, facilitating the fabrication of p‐n heterojunction OPDs based‐on PBB and 6,6‐phenyl‐C71‐butyric acid methyl ester (PC71BM) using either chloroform (CF) or o‐xylene (Xy). Notably, Xy‐processed OPDs show superior performance with a responsivity (R) of 0.385 A W−1 and specific detectivity (D*) of 1.33 × 1013 Jones at –1 V, whereas CF‐based devices showed an R of 0.349 A W−1 and D* of 5.86 × 1012 Jones. More importantly, Xy‐processed OPDs exhibited an ultrafast signal response time of 3 µs, which is much faster than that of CF‐processed OPDs (42 µs). These superior static and dynamic properties of PBB:PC71BM devices are achieved by the inverted hierarchical arrangement of PBB and PC71BM via a biased orientation of PC71BM toward the ZnO layer as well as a homogenous nanomorphology. This ideal morphology is spontaneously induced due to the difference in interfacial energy between PBB and PC71BM toward the ZnO surface and a well‐mixed PBB:PC71BM blend in Xy solvent.
Funding Information
  • National Research Foundation of Korea (2021R1G1A1011510, 2016R1A6A1A03013422, 2020M3H4A3081816)

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