Large-scale roll-to-roll printed, flexible and stable organic bulk heterojunction photodetector

Abstract A flexible and stable photodetector shows great potential applications in intelligent wearable devices, health monitoring, and biological sensing. The high-output fabrication of flexible and stable photodetector via the large-scale printing process would accelerate its commercialization. Herein, a high performance, flexible organic bulk heterojunction (BHJ) photodetector with good stability is designed and fabricated via a large-scale roll-to-roll (R2R) micro-gravure printing technique on polyethylene terephthalate (PET) or paper substrate, in which the organic BHJ active layer is structured with [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) and a donor–acceptor copolymer, i.e., employing 4,8-bis(2-ethylhexylthiophene) benzo[1,2-b;3,4-b′] dithiophene (BDTT) as the donor unit and 5,8-bis(5-thiophen-2-yl)-6,7-difluoro-2,3-bis(4-ethylhexyloxy-1-mata-luorophenyl) quinoxaline (ffQx) as the acceptor unit (PBDTT-ffQx). The PBDTT-ffQx/PCBM BHJ photodetector shows a broad photoresponse in ultraviolet and visible light, a high detectivity (D*) value up to 6.19 × 10¹¹ Jones, and an excellent I_photo/I_dark as high as 5.6 × 10². It exhibits excellent flexibility and stability. Its performance parameters could maintain over 80% of original values after bending 10,000 cycles or exposing in ambient condition (humidity ~50%, temperature ~30 °C) for 50 days without any encapsulation. More importantly, the R2R micro-gravure printed PBDTT-ffQx/PCBM BHJ active layer is great homogeneous, and the responsivity (R) values of photodetector arrays show a very narrow distribution. The research results show that a high-performance PBDTT-ffQx/PCBM BHJ photodetector with well reliability and reproducibility can be fabricated via the R2R micro-gravure printing technique, which provides an available strategy for fabricating large-area and flexible electronic and optoelectronic devices.