A comprehensive investigation of organic active layer structures toward high performance near-infrared phototransistors

Tin phthalocyanine (SnPc) is a kind of organic semiconductor material with excellent absorbing characteristic in near-infrared (NIR) region but rarely applied in photosensitive organic field-effect transistors (PhOFETs). Here, a series of SnPc based PhOFETs with different active layer structures were fabricated and characterized for the purpose of making a systematic investigation of organic active layer structure toward NIR phototransistors. Among the sample devices with different active layer structures, the tri-layer planar heterojunction structure of Device C exhibits high photoresponsivity of 2686.1 mA/W and the photosensitivity is up to 104. The tri-layer hybrid planar-bulk heterojunction configuration of Device D also possesses excellent overall performance, whose photoresponsivity reaches 1894.7 mA/W and photosensitivity is up to 5925. Meanwhile, the detectivity remains at the level of 1012 Jones. After a comprehensive investigation of different organic active layer structures, some useful design principles for NIR phototransistors are obtained. While the mobility of SnPc is relatively low, the photosensitive performance of the devices can be improved to various extent by applying planar and hybrid planar-bulk heterojunction configuration. Given the similar features of some organic NIR materials, we believe that the device design concepts we used for SnPc can be helpful to guiding and designing higher performance NIR phototransistors based on other organic materials.