Tailoring Hole‐Blocking Layers Enables a Versatile Approach for Fast Photomultiplication‐Type Organic Photodetectors

Abstract Organic photodetectors (OPDs) are promising for various applications due to their cost‐effectiveness in fabrication, flexibility, and tunable response to specific wavelengths. Their excellent sensitivity enables multiple applications in imaging, healthcare, and security monitoring. Notably, photomultiplication‐type organic photodetectors (PM‐OPDs) offer distinct advantages due to their internal amplification mechanism. In this work, a strategy is presented for employing two hole‐blocking layers (HBLs) to improve the photodetection capabilities of PM‐OPDs. A systematic exploration of the HBL material combination reveals the importance of shallow lowest unoccupied molecular orbital (LUMO) and deep highest occupied molecular orbital (HOMO) levels for optimal performance. Utilizing HBLs with deep HOMO levels, HAT(CN) 6 and C 60 , leads to enhanced hole accumulation, resulting in a distinct photomultiplication effect. Optimized devices exhibit an impressive external quantum efficiency (EQE) surpassing 1290%, shot‐noise limited specific detectivity of 1.7 × 10 12 Jones (2.4 × 10 11 Jones based on noise measurements), and a rapid cutoff frequency exceeding 40 kHz, representing a significant advancement in PM‐OPD capabilities. Moreover, this device architecture surpasses current limitations by ensuring compatibility with various photoactive layers with balanced donor‐acceptor stoichiometry. Our results confirm this universal approach, which enables high‐gain PM‐OPDs across spectral ranges while maintaining fast response speeds.