Molecular Order Control of Nonfullerene Acceptors Enables Ultralow Dark Current and High Responsivity in Short-Wavelength Infrared Organic Photodetectors

Developing organic semiconductors for short-wavelength infrared (SWIR) organic photodetectors (OPDs) remains challenging due to the trade-off between achieving a long-wavelength spectral response and high external quantum efficiencies (EQEs) as well as low dark current densities (J_d). Herein, two spiro-structural nonfullerene acceptors (NFAs) with responses reaching 1200 nm, namely DPA-4F and TPA-4F, were developed. By changing the substituent on the spiro-core unit from a hexyl chain to a phenyl group, TPA-4F displayed an ordered three-dimensional stacking network with “head-to-tail” interactions between terminal groups and “core-to-core” interactions between spiro-core units. The enhancement in the molecular order of TPA-4F was demonstrated to effectively red-shift the spectral response, decrease the energetic disorder, and reduce the trap density of states in OPDs. Consequently, a high EQE of more than 40% from 600 to 1060 nm at 0 V bias and a low J_d of 2.61 × 10^-10 A/cm² at −0.1 V could be simultaneously realized for TPA-4F-based devices, resulting in a detectivity (D*) exceeding 10¹³ Jones, ranked the highest value for SWIR OPDs. Furthermore, the obtained OPDs can be integrated into flexible large-area photoplethysmography sensors for pulse signal monitoring even without external SWIR light irradiation. These findings shed light on the design of NFAs for highly detective SWIR OPDs in practical applications.