Study On High-performance Small-molecular Photoresponsive Organic Field-effect Transiators

Organic field effect transistor (OFET) is one of the main research directions of organic electronics. Photoresponsive organic field-effect transistor (PhotOFET) is one of the special applications of OFETs. As a new type of optoelectronic devices, PhotOFETs can be applied to areas including optical switches, photo-sensors, and photo detectors etc. Compared with the conventional inorganic photo detectors, PhotOFETs have wider spectrum of response and higher photoresponsivity. The flexible and portable PhotOFETs can be realized by fabricating on the flexible substrates. Additionally, compared with organic photodiodes, PhotOFETs integrate the functions of the light detection and the signal amplification in one device, and they have higher sensitivity and lower noise level.Small molecule organic semiconductors have constant molecular weight, stable structure and physical properties, which are benefit for forming a regular and orderly solid film. Besides, PhotOFETs based on organic small molecules are very suitably fabricated by vacuum evaporationa simple physical vapor deposition method. Thus, we choose small-molecule organic semiconductor materials as the active layer materials of PhotOFETs in this study. Several kinds of PhotOFETs based on small-molecule have been designed and fabricated. And the effects of the source/drain electrode materials and the electrode buffer layer on PhotOFETs’performances have been investigated.(1) It has been proved that the Schottky contact at the interface between Al electrodes and (palladium phthalocyanine, PdPc) active layer can effectively increase the photocurrents of the PhotOFETs based on PdPc. Moreover, the Al-PdPc PhotOFET can obtain high photoresponsivity and high photosensitivity simultaneously when it works in the ON-state. Additionally, the effects of source/drain electrode materials on the pentacene-PhotOFETs (PENT-PhotOFETs)’ performances are also investigated in this dissertation.(2) The height of hole injection energy barrier between gold and pentacene can be reduced by inserting a C60electrode buffer layer under gold source and drain electrodes in PENT-PhotOFETs. Compared with the device without modification, the C60modified PENT-PhotOFETs have higher field effect mobility, lower threshold voltage and larger photoresponsivity. The highest photoresponsivity of C60modified device can reach4.27A/W, which is higher than that of the most currently reported PhotOFETs. Meanwhile, the device also obtains high photosensitivity of about5×104. We have further optimized the thickness of C60electrode buffer layer in the experiment and investigated the effects of the surface roughness of the active layer on the optimized buffer layer thickness in PhotOFETs.(3) A novel structure of hybrid planar/bulk heterojunction (HPBHJ) is introduced for designing of near-infrared PhotOFETs. Compared with the conventional single and double heteroj unction and the single active layer PhotOFETs, HPBHJ-PhotOFETs exhibit excellent photosensitivity properties. It is demonstrated that the performances of PhotOFETs can be improved by adopting HPBHJ structure which is made of bulk-heterojunction exciton-generating layer and high-mobility carrier transport layer.