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.