Abstract
As a promising candidate for next-generation photodetectors, organic photodetectors (OPDs) have gained increasing interest as they offer cost-effective fabrication methods using solution processes and a tunable spectral response range, making them particularly attractive for large area image sensors on lightweight flexible substrates. Carrier blocking layers engineering is very important to the high performance of OPDs that can select a certain charge carriers (holes or electrons) to be collected and suppress another carrier. Carrier blocking layers of OPDs play a critical role in reducing dark current, boosting their efficiency and long-time stability. This Review summarizes various materials for carrier blocking layers and some of the latest progress in OPDs. This provides the reader with guidelines to improve the OPD performance via carrier blocking layers engineering.
Highlights
The working mechanism of organic photodetectors (OPDs) is similar to that of organic photovoltaics (OPVs), which can be summarized as (i) the organic semiconductors absorb photons to generate excitons and the excitons diffuse to donor/acceptor interfaces; (ii) the excitons separate into electrons and holes driven by electric field force formed by extra applied bias; (iii) holes are transferred to the anode through the channels formed by the highest occupied molecular orbital (HOMO) of the donor, and electrons are transported to the cathode via the channels formed by the lowest unoccupied molecular orbital (LUMO) of the acceptor; (iv) the holes and electrons are collected by the corresponding electrode to generate photocurrent
Figures of merit of OPDs have been summarized in the literature [13,14], here we provide a comprehensive definition of the most important figures of merit to enable a clear understanding of reported OPD performances and key points of attention
In bulk heterojunction (BHJ) Photomultiplication-type organic photodiodes (PM-OPDs), it was revealed that Bromide of PFN (PFN–Br) reduced the work function of ITO to achieve effective Schottky junctions with polymer donor materials, and efficiently enhanced the trapping efficiency, which can be ascribed to electrostatic interactions between the positively charged quaternary ammonium groups and trapped electrons within the isolated (6,6)-phenyl C71 butyric acid methyl ester (PC71BM) domains
Summary
Photodetectors can convert optical signals to electronic signals, which are widely applied in optical communication, environmental monitoring, cameras, smart phones, image sensing, and so on [1,2,3,4,5]. The basic structure of OPDs generally includes two essentials parts: an active layer for light absorption and electrodes for the collection of charge carriers (electrons and holes). Improving the high gain property, OPDs have achieved significant breakthroughs and rapid evolution in the last several decades, thanks to the developments of novel donor/acceptor materials, the innovations of the device structure, and interface engineering. Due to the lower relative permittivity (εr ≈ 3–4) of organic in comparison with inorganic materials [11], excitons with a relatively high binding energy of ≈ 0.35–0.5 eV are generated after light absorption, rather than free electrons and holes. The active layer of OPDs is often based on a bulk heterojunction (BHJ) architecture that comprises finely bicontinuous and interpenetrative networks of electron donor and acceptor phases, in which this structure facilitates exciton dissociation and charge transport to the relevant electrodes [12]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call