Synergistic Reduction of Localized Trap States and Dark Current in Organic SWIR Photodetectors Enabled by a Ternary...

Trap states in the bulk heterojunction (BHJ) active layer can deleteriously affect the performance of short wave infrared organic photodiodes (SWIR OPDs). Herein, a ternary blend strategy, using three Y-series non-fullerene acceptors as guest components, is employed to control the trap states in the BHJ active layer of SWIR OPDs. The judiciously chosen third component modulates molecular aggregation and lowers energetic disorder, thereby facilitating favourable charge-transport pathways through acceptor-alloy formation. The guest component effectively suppresses the dark current density to 3.94 nA cm^-2 at -1 V in the optimized device. Moreover, the third component incorporation increases the thermal activation energy, as revealed from Arrhenius analysis, indicating suppressed trap-assisted transport. Capacitance-frequency measurements further confirm a reduction in the trap states within the active layer. Consequently, the optimized ternary devices deliver a specific detectivity of 3.56 × 10¹² Jones at λ ≈ 1000 nm, along with superior operational stability compared to binary devices. Furthermore, the fabricated photodetectors demonstrate applicability in spectroscopic measurements, successfully recording molecular absorption spectra in good agreement with data from a standard spectrometer. Overall, this study establishes a generalized strategy to mitigate trap states and enhance charge transport, thus improving the detectivity of SWIR OPDs.