RESUMO
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, we have developed a new PM-type OPD that demonstrates ultrafast dynamic properties through a vertical phase separation (VPS) strategy between the p-type polymer (host) and n-type acceptor (dopant), referred to as VPS PM-type OPDs. Notably, VPS PM-type OPDs show a remarkable increase (by three orders of magnitude) 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 1,121% and specific detectivity of 2.53 × 1013 Jones at -10 V. The VPS PM 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. This article is protected by copyright. All rights reserved.
RESUMO
Suppressing the dark current density (Jd) while maintaining sufficient charge transport is important for improving the specific detectivity (D*) and dynamic characteristics of organic photodetectors (OPDs). In this study, we synthesized three novel small-molecule acceptors (SMAs) densely surrounded by insulating alkyl side chains to minimize the Jd in OPDs. Introducing trialkylated N-annulated perylene diimide as a terminal moiety to the alkylated π-conjugated core structure was highly efficient in suppressing Jd in the devices, resulting in an extremely low Jd of 4.60 × 10-11 A cm-2 and 10-100 times improved D* values in the devices. In addition, SMAs with a geometrically aligned backbone structure exhibited better intermolecular ordering in the blended films, resulting in 3-10 times as high responsivity (R) values in the OPDs. Outstanding OPD performances with a D* of 8.09 × 1012 Jones, -3 dB cutoff frequency of 205.2 kHz, and rising response time of 16 µs were achieved under a 530 nm illumination in photoconductive mode. Geometrically aligned core-terminal SMAs densely surrounded by insulating alkyl side chains are promising for improving the static and dynamic properties of OPDs.
RESUMO
Colloidal quantum dots (CQDs) have a unique advantage in realizing near-infrared (NIR) photodetection since their optical properties are readily tuned by the particle size, but CQD-based photodetectors (QPDs) presently show a high dark current density (Jd) and insufficient dynamic characteristics. To overcome these two problems, we synthesized and introduced two types of conjugated polymers (CPs) by replacing the p-type CQD layer in the QPDs. The low dielectric constant and insulating properties of CPs under dark conditions effectively suppressed the Jd in the QPDs. In addition, the energy-level alignment and high-hole mobility of the CPs facilitated hole transport. Therefore, both the responsivity and specific detectivity were highly enhanced in the CP-based QPDs. Notably, the dynamic characteristics of the QPDs, such as the -3 dB cut-off frequency and rising/falling response times, were significantly improved in the CP-based QPDs owing to the sizable molecular ordering and fast hole transport of the CP in the film state as well as the low trap density, well-aligned energy levels, and good interfacial contact in the CP-based devices.
