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-dioctylfluorenyl2,7- diyl)-alt-co-(bithiophene)] (F8T2), combined disproportionately with the fullerene-derivative [6,6]-phenyl-C-71-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 x 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.