Mechanistic insights into additive-driven dark current and responsivity in organic photodetector with varied film thickness

Organic photodetectors (OPDs) have garnered significant attention due to their advantages of low manufacture cost, high absorption coefficient, tunable energy level, and mechanic flexibility. We selected the low-energy-gap donor material PTB7-Th and the fullerene acceptor PC₇₁BM to form the active layer in a bulk-heterojunction (BHJ) structure, and the aggregation of PC₇₁BM was modulated by adjusting the ratio of the additive 1,8-diiodooctane (DIO). Our investigation focused on both thin and thick film OPDs performance. The addition of DIO enhanced dark current suppression and significantly improved the responsivity, particularly in thin film-based OPDs. Thick film OPDs also exhibited better dark current suppression and responsivity. The best OPD performance was achieved at a reverse bias of −3 V, yielding a noise current of 6.7 × 10⁻¹⁴ A, a responsivity of 0.37 A/W, and a specific detectivity (D_n^⁎) of 2.94 × 10¹² Jones. Notably, the effect of DIO on dark current differs between thick and thin films. The results of this study indicate that noise performance in thick film-based devices is primarily dominated by thermal noise, while changes in surface morphology and structural optimization mainly affect responsivity. Our findings clarify the mechanisms affecting OPD performance and pave the way for the development of high-performance OPDs.