Dual-benefit strategy for developing an efficient photodetector with prompt response to UV-near IR radiations: in situ synthesis and crystallization through a simple one-step annealing

Abstract

Photodetecting units are widely used in various areas. Among all, organic photodetectors are given particular attention because of their promising applications in developing wearable and flexible devices. In this work, octyl (C8)-diketopyrrolopyrrole (DPP)-tetrabenzoporphyrin (BP)/graphene (G) films were fabricated with a design inspired by “killing two birds with one stone”. The in situ synthesis of C8-DPP-BP from its precursor/G films and the formation of highly crystallized morphologies were performed through a simple one-step annealing technique. C8-DPP-BP/G transistors show a broadband response to radiations from the ultraviolet to near infrared region. With a sufficiently long annealing time (6 h), the photodetection responsivity (R) and specific detectivity (D*) are promoted 5–10 folds compared with the film with a short time (3 hours, 3 h), while the fast on/off speeds are not deteriorated (the enhancements of R and D* vary slightly with different radiations). By analyzing the morphologies of 6 h and 3 h C8-DPP-BP/G films, we suggest that the reduced boundaries in the large sheets of 6 h C8-DPP-BP/G films and the highly crystallized end-on arrangements in the vertical direction are the key structural factors for the great improvements in R and D* while keeping the fast operation speed unaffected. Charge carriers can transport within the 6 h C8-DPP-BP film in a less interrupted way, and the separation of charge carriers near the interface of C8-DPP-BP and G is facilitated by the large distance between the center of end-on C8-DPP-BP and the G plane. Thus, in this work, besides developing an efficient broadband photodetector, we also revealed the key structural features supporting the great improvements in photosensing applications, which is of importance for understanding the complicated relationships between the morphologies and optoelectronic performances of organic films.