Self-Assembling Hole-Transport Molecules Enable Photomultiplication-Type Organic Photodetectors with High Detectivity and Enhanced Environmental Stability

Photomultiplication-type organic photodetectors (PM-OPDs) have attracted significant attention for their high gain and simplified device architecture. However, their practical application is severely constrained by the high dark current density inherent to charge injection-type multiplication mechanisms, which compromises specific detectivity (D*), as well as the poor environmental stability associated with conventional acidic and hygroscopic interlayers. Herein, we demonstrate that replacing the conventional PEDOT:PSS hole-transport layer with a self-assembled monolayer of 1F-2PACz not only dramatically suppresses dark current but also significantly enhances device robustness. In PM-OPDs with a P3HT:PC71BM (100:1, w/w) active layer, the 1F-2PACz-modified devices effectively suppress electron back-injection owing to the high work function and electron-blocking lowest unoccupied molecular orbital level of 1F-2PACz, exhibiting a dark current one order of magnitude lower than PEDOT:PSS-based counterparts, resulting in a high specific detectivity exceeding 1013 Jones. Mechanistic investigations reveal that 1F-2PACz facilitates faster hole extraction and mitigates interfacial trap-mediated recombination. Crucially, the hydrophobic nature of the fluorinated carbazole moiety endows the devices with superior water resistance and long-term stability; the device maintains stable performance after direct water immersion for 30 min and continuous storage for 60 days. This work demonstrates that self-assembling hole-transport molecules provide a robust strategy for simultaneously achieving high gain, low noise, and excellent stability in PM-OPDs.