Organic Ultraviolet Photodetectors Exhibiting Photomultiplication, Low Dark Current, and High Stability

Abstract

Organic UV photodetectors can provide a cheap, durable alternative to current technologies used for applications such as missile detection and arc flash protection. The wide‐bandgap semiconductor poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐alt‐co‐(bithiophene)] (F8T2), combined disproportionately with the fullerene‐derivative [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) in weight ratios of 100:4 and 100:1, comprises the active layers of organic UV photodetectors. The small clusters of PC71BM trap charges, enhancing band bending and charge injection and thus enabling photomultiplication. These clusters also prevent electrons from transporting through the device, helping produce a low dark current. Although devices without an electron transfer layer (ETL) exhibit more efficient photomultiplication, they tend to be unstable. Devices with a F8T2:PC71BM weight ratio of 100:4 and with an ETL demonstrate an external quantum efficiency peaking at 5600%, at 360 nm and −40 V bias, and a low dark current of 2.7 × 10−7 mA cm−2 at −1 V bias. These devices are stable and behave well even under strong biases, which enhance the UV‐selectivity and response speed of the devices.

Recent Progress on Photomultiplication Type Organic Photodetectors

“…Similar to highly sensitive OPDs with P3HT:PC 71 BM (100:1) as active layer, Yu et al. demonstrated the PM type OPDs utilizing blend active layers of poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐alt‐co‐(bithiophene)] (F8T2) and PC 71 BM in weight ratios of 100:4 or 100:1, with and without the LiF interfacial ETL/HBL layer . The schematic working mechanism is exhibited in Figure .…”

“…The relative band energies of used materials: in dark a) without and b) with applied reverse bias; c) under light illumination with applied reverse bias and the resulting PM mechanism. All panels reproduced with permission . Copyright 2017, Wiley‐VCH.…”

“…[149] The ternary strategy, as an effective method of achieving high-efficiency organic solar cells, has been widely employed. [150][151][152][153][154][155][156][157][158] The OPDs with broadband response were successfully demonstrated by doping poly [4,8- [46] The schematic working mechanism is exhibited in Figure 14. The small PC 71 BM clusters can capture photogenerated electrons, the trapped electron may induce interfacial band bending for efficient hole tunneling injection, resulting in PM phenomenon.…”

“…[36] Inspired by this work, a series of PM type OPDs are realized during the past decades. [37][38][39][40][41][42][43][44][45][46][47] There are many efforts concentrated on the research of the working mechanisms of PM, [48][49][50][51][52] the improvement of device performance, [53][54][55][56][57][58][59] and the adjustment of spectral response window. [60][61][62][63][64] However, to date, a comprehensive review about PM type OPDs has not yet been published.…”

On the Origin of Dark Current in Organic Photodiodes

“…[13] Photomultiplication is another strategy to enhance OPD performance. [14][15][16] However, despite the importance of J d , a quantitative relation between its magnitude and BHJ properties, such as the energetic landscape and charge transport characteristics, remains unestablished. This study aims to clarify the relationship between J d and the properties of the organic semiconductor blend, with a view to providing material selection guidelines to improve BHJ OPD sensitivity.Herein, we investigate J d in BHJ OPDs based on five different polymer donors with widely varying optical bandgaps, each combined with a common fullerene acceptor.…”