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

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.