Organic photodetectors (OPDs) are promising candidates for low-cost, high-sensitivity imaging and sensing applications, yet their performance remains limited by interfacial recombination and high dark currents. Here, we introduce a molecular interfacial engineering strategy based on a phosphonic acid-functionalized self-assembled monolayer (2PACz) to simultaneously modulate energy-level alignment and suppress trap-assisted leakage at the bulk heterojunction/MoO x interface. The 2PACz layer reduces the MoO x work function from 4.96 eV to 4.26 eV, increasing the electron injection barrier from 0.21 eV to 1.49 eV and effectively minimizing reverse leakage current. Concurrently, interfacial trap passivation broadens the depletion region and enhances exciton dissociation and carrier extraction, leading to prolonged carrier lifetimes. As a result, the optimized OPDs exhibit a two-order-of-magnitude reduction in dark current density (from 10 −8 to 10 −10 A cm −2 ), a high specific detectivity exceeding 1.5 × 10 13 Jones in the near-infrared range, and fast response times (τᵣ/τ f = 5.8 μs/5.9 μs). These low-noise devices enable high-fidelity photoplethysmography (PPG) biosensing with an improved signal-to-noise ratio (10 to 18 dB), multi-channel spectral laser decoding, and ultra-weak starlight (~10 −10 W cm −2 ) imaging using an 8 × 8-pixel OPD array. This work provides a generalizable and scalable interfacial design framework for advancing solution-processed OPDs toward next-generation ultrasensitive optoelectronics. Surface molecular engineering using self-assembled monolayers (SAMs) suppresses noise current by tuning injection barriers and passivating traps, enabling organic photodetectors with >10 13 Jones detectivity for starlight imaging, biosensing, and spectral decoding. • Self-assembled monolayers passivate traps and build blocking energy levels • Dark current suppressed by two orders (10 −8 to 10 −10 A cm −2 ) • Record detectivity (1.5 × 10 13 Jones) and linear dynamic range (156 dB) • Starlight imaging (10 −10 W cm −2 ) using an 8 × 8 organic photodetector array
Zhang et al. (Tue,) studied this question.