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.