Vertically Phase Separated Photomultiplication Organic Photodetectors with p‐n Heterojunction Type Ultrafast Dynamic Characteristics

Abstract Photomultiplication (PM)‐type organic photodetectors (OPDs), which typically form a homogeneous distribution (HD) of n ‐type dopants in a p ‐type polymer host (HD PM‐type OPDs), have achieved a breakthrough in device responsivity by surpassing a theoretical limit of external quantum efficiency (EQE). However, they face limitations in higher dark current and slower dynamic characteristics compared to p‐n heterojunction ( p‐n HJ) OPDs due to inherent long lifetime of trapped electrons. To overcome this, a new PM‐type OPD is developed that demonstrates ultrafast dynamic properties through a vertical phase separation (VPS) strategy between the p ‐type polymer and n ‐type acceptor, referred to as VPS PM‐type OPDs. Notably, VPS PM‐type OPDs show three orders of magnitude increase in −3 dB cut‐off frequency (120 kHz) and over a 200‐fold faster response time (rising time = 4.8 µs, falling time = 8.3 µs) compared to HD PM‐type OPDs, while maintaining high EQE of 1121% and specific detectivity of 2.53 × 10 13 Jones at −10 V. The VPS PM‐type OPD represents a groundbreaking advancement by demonstrating the coexistence of p‐n HJ and PM modes within a single photoactive layer for the first time. This innovative approach holds the potential to enhance both static and dynamic properties of OPDs.