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End-Group Engineering of Low-Bandgap Compounds for High-Detectivity Solution-Processed Small-Molecule Photodetectors

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journal contribution
posted on 12.11.2015, 00:00 by Ji Qi, Jinfeng Han, Xiaokang Zhou, Chang Guo, Dezhi Yang, Wenqiang Qiao, Yuning Li, Dongge Ma, Zhi Yuan Wang
Several π-conjugated compounds based on diketopyrrolopyrrole and trithiophene substituted with different end groups (alkyl, alkyloxy, and alkylthio) were designed and synthesized for investigation of the material properties and photodetector performance brought by subtle changes in the end groups. Among all, compound 4 with hexylthio groups exhibits the most red-shifted absorption, strongest molecular stacking, highest mobility, and ideal film morphology. These unique properties make it a promising material for use in small-molecule photodetectors. Photodetector SMPD-4 based on compound 4 exhibits broad response from 300 to 900 nm and a high specific detectivity (D*) of 1.3 × 1013 Jones at 650 nm under −0.1 V. This result is among the best values reported for solution-processed small-molecule photodetectors and even in the same order of conventional silicon photodetector. The molecular structure–material property–device performance relationships are established with these compounds. This work suggests that end-group engineering is a useful method in tuning the material properties and device performance of organic semiconductors.