On the Response Speed of Narrowband Organic Optical Upconversion Devices

摘要

Organic upconversion devices (OUCs) consist of an organic infrared photodetectorand an organic visible light-emitting diode (OLED), connected in series.OUCs convert photons from the infrared to the visible and are of use inapplications such as process control or imaging. Many applications require afast OUC response speed, namely the ability to accurately detect in the visiblea rapidly changing infrared signal. Here, high image-contrast, narrowbandOUCs are reported that convert near-infrared (NIR) light at 980 and 976 nmwith a full-width at half maximum of 130 nm into visible light. Transientphotocurrent measurements show that the response speed decreases whenlowering the NIR light intensity. This is contrary to conventional organicphotodetectors that show the opposite speed-versus-light trend. It is furtherfound that the response speed increases (when using a phosphorescentOLED) or decreases (for a fluorescent OLED) when increasing the drivingvoltage. To understand these surprising results, an analysis by numericalsimulation is conducted. Results show that the response speed behavior isprimarily determined by the electron mobility in the OLED. It is proposed thatthe low electron drift velocity in the emitter layer sets a fundamental limit tothe response speed of OUCs.