Effect of Cyano Substitution on Non‐Fullerene Acceptor for Near‐Infrared Organic Photodetectors above 1000 nm

Abstract

Near‐infrared organic photodetectors (NIR OPDs) comprising ultra‐narrow bandgap non‐fullerene acceptors (NFA, over 1000 nm) typically exhibit high dark current density under applied reverse bias. Therefore, suppression of dark current density is crucial to achieve high‐performance of such NIR OPDs. Herein, cyano (CN) with a strong electron‐withdrawing property is introduced into alkoxy thiophene as a π‐bridge to adjust its optoelectronic characteristics, and the correlation between dark current density and charge injection barrier is investigated. Compared with their motivated NFA (COTH), the novel CN‐substituted NFAs, COTCN and COTCN2, exhibited deeper‐lying highest occupied molecular orbital energy levels and narrower optical bandgap (<1.10 eV), owing to the strong inductive and resonance effect of CN. The dark current and total noise currents are minimized as the number of substituted CN increases because of the larger hole injection barrier. Consequently, PTB7‐Th:COTCN2 exhibited the best shot‐noise limited detectivity (D*sh, 1.18 × 1012 Jones) and total noise detectivity (D*n, 1.33 × 1011 Jones) compared with those of PTB7‐Th:COTH (D*sh, 2.47 × 1011 Jones and D*n, 1.96 × 1010 Jones).

A Direct surface modification strategy of ITO anodes enables high-performance organic photodetectors

“…5b). 7 The R sh values of the devices based on ITO-Cl and ITO/PEDOT:PSS are 1.25 MΩ and 850 kΩ, respectively. The higher R sh value of the ITO-Cl device indicates that the device has a larger electron injection barrier, which corresponds to its lower J d .…”

“…In recent years, organic photodetectors (OPDs), which consist of the active layer of the bulk heterojunction sandwiched between two electrodes, have attracted extensive attention due to their inherent advantages, such as solution processing, response range tunability, flexibility, and low energy consumption. [1][2][3][4][5][6][7] These advantages give OPDs potential in many fields, such as optical communication, medical monitoring, artificial vision, etc. For OPDs, low dark current density ( J d ) is crucial to achieving sensitive light detection capability.…”

“…[8][9][10] J d is the output current of devices under bias in dark conditions, which is mainly attributed to the carrier injection rate from the contact into the semiconductor, or the thermal generation rate of carriers within the active layer. Over the years, various solutions, such as reducing pinholes and film imperfections, 11,12 preventing unfavorable charge injection, [13][14][15][16] improving charge selectivity at the contacts, [17][18][19][20] and optimizing the active layer materials and vertical phase segregation structure, 7,[21][22][23] have been used to reduce the dark current of OPD devices. Among them, interface modification of the contact is proved to be a potential strategy for blocking charge and thus suppressing J d .…”

Vacuum-deposited organic photodetectors utilizing non-fullerene acceptors for enhanced detectivity in the green visible light spectrum

“…15 Additionally, if the distance between the conduction band MoO 3 and the LUMO acceptor is small, as well as the distance between the LUMO acceptor and the LUMO donor is also narrow, it is easier for electrons to penetrate the active layer of devices C and D compared to devices A and B. 55…”

Anisotropic Organic Magnetoresistance in Fused-Ring Electron-Acceptor-Based Bulk Heterojunction Systems

“…Fused-ring electron acceptors (FREAs)-based organic bulk heterojunctions (BHJs), also known as nonfullerene acceptors-based organic BHJs, have received tremendous attention, due to their critical role for improvements of photovoltaic power conversion efficiencies (PCE) to completely high levels. − Apart from organic solar cells (OSCs), they have been successfully applied for organic photodetectors (OPDs), − organic dopants, and transport layers in various types of hybrid devices, such as organic-perovskite tandem solar cells and sensors. − Indeed, all signal generations, transmissions, and detections of those devices rely on the electronic charge property. One critical question may arise: can the electronic spin degree of freedom be effectively manipulated in the FREA-based organic BHJs?…”