High performance organic transistors and phototransistors based on diketopyrrolopyrrole-quaterthiophene copolymer thin films fabricated via low-concentration solution processing

Abstract Conjugated polymers have received considerable attentions over the past years due to their large-area potential applications via low-cost solution processing. Improving crystallinity of conjugated polymer molecules in solution-processed thin films is crucial for their efficient charge transport and thus high performance optoelectronic devices. Herein, with diketopyrrolopyrrole-quaterthiophene (PDQT) copolymer as an example, it is found that by simply reducing the solution concentration for spin-coating meanwhile with the assistance of post-annealing, significantly enhanced film crystallinity with formation of typical single crystalline domains is obtained, which benefits from the enough space for better molecular assembly especially at the semiconductor/dielectric interface. High performance polymer transistors and phototransistors were finally constructed based on the optimal low-concentration (2 mg/mL) spin-coated PDQT films (∼12 nm), which giving a high charge carrier mobility of 2.28 cm 2  V −1  s −1 and a photoresponse on/off ratio of 2.1 × 10 7 at V G  = 0 V under white light irradiation of 6 mW/cm 2 . The results suggest that the bright future of PDQT crystalline films for large-area flexible integrated optoelectronic devices and the application of effective low-concentration processing approach in solution-processed organic electronics with reduced material waste.