Enabling a High-Sensitivity and Fast-Response Organic Phototransistor Based on an "Embedded" Heterojunction toward Broadband High-Speed Imaging

Organic phototransistors (OPTs) are promising candidates for broadband light detection, offering advantages of spectral tunability, cost-effectiveness, and flexibility. Nonetheless, their practical utility has been impeded by issues such as low exciton dissociation efficiency and persistent photoconductivity. To address this challenge, an electron acceptor (TCNQ) was doped in pentacene as the donor, resulting in the formation of self-organized "embedded" heterojunctions within a single-crystal matrix. This unique organic architecture led to the development of high-performance OPTs, boasting an exceptional photoresponsivity of 1.1 x 10(4) A W-1 and a specific detectivity of 2.1 x 10(13) Jones. Importantly, the device exhibited a fast response time of about 92 mu s, maintaining a high photosensitivity exceeding 100, surpassing the capability of detectors constructed from pure organic single crystals. Notably, this "embedded" heterojunction design also enabled the superior infrared photoresponse at 1550 nm by narrowing the band gap. The enhanced performance is a result of the efficient separation of Frenkel excitons and collection of free charges driven by the built-in field at the "embedded" pentacene/TCNQ interface. Furthermore, these OPTs demonstrated versatility in capturing high-resolution images across multiple spectral bands, emphasizing the potential of molecule doping to enhance organic photodetector performance as a straightforward alternative.