Nanowire-Induced Vertical Phase Separation Enables Dark-Current Suppression and High Bandwidth in Single-Layer Organic Photodetectors

Suppressing dark current while preserving charge extraction and bandwidth remains a key challenge for organic photodetectors (OPDs), because conventional carrier-blocking strategies often compromise photocarrier transport. Here, we report a morphology-driven strategy based on water-bath-assisted self-assembly of poly(3-hexylthiophene) (P3HT) nanowires in a single-layer donor-acceptor bulk heterojunction. These preassembled nanowires direct vertical phase separation of the blend, creating a morphology-controlled carrier-injection pathway that suppresses leakage current under reverse bias while retaining efficient photocarrier extraction. Spectroscopic analyses reveal that nanowire formation redistributes the donor-acceptor components along the vertical direction, creating an energetically favorable architecture that blocks undesired carrier injection while maintaining directional charge transport. As a result, the fabricated photovoltaic-type photodetectors exhibit a shot-noise-limited specific detectivity (D*sh) of 1.50 × 1012 jones, a linear dynamic range (LDR) of 144.2 dB, and a -3 dB cutoff frequency of 4.94 MHz. Additionally, the ZnO-modified photoconductive device yields a D*sh of 1.90 × 1013 jones and an LDR up to 160.1 dB while preserving an 8.45 MHz bandwidth, achieving state-of-the-art performance across both photovoltaic and photoconductive OPD architectures. This work establishes nanowire-induced vertical phase separation as a morphology-design principle for regulating carrier injection in organic optoelectronic devices, providing new insights into simultaneously achieving suppressed dark current, wide dynamic range and multimegahertz bandwidth in simplified device architectures.