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 × 10¹³ 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.