Organic phosphorescent UV photodetector is visible-blind

Scientists at Beijing Jiao Tong University (Beijing, China) have created an organic solar-blind UV photodetector by using two different phosphorescent materials as the electron donor and acceptor, termed FIrpic and PCBM, respectively. The use of organic materials for such devices enables device flexibility, as well as low-cost manufacture in large sheets. The researchers realized that the choice of phosphorescent, rather than fluorescent, materials could lead to improved devices. Noting that organic UV photodiodes using phosphorescent materials were rarely discussed, they decided to give it a try.

The devices were fabricated by coating the materials onto glass covered with a film of indium tin oxide; a 100-nm-thick aluminum cathode layer was then deposited on top. The detectors, which had a 3 × 3 mm active area, were tested under a pulsed (square-wave) UV (365 nm) source to see their transient response; under a -13 V reverse bias, the devices showed rise and fall times of less than 1 s (phosphorescent materials tend to have slow response). Under steadier light, the devices showed a linear response over light intensities ranging from 0.018 to 20 mW/cm². Peak responsivity was 140 mA/cm² at 0.018 mW/cm², reaching an external quantum efficiency (EQE) of 48% and a detectivity of 2.4 × 1011 Jones; at higher intensities the EQE dropped off, dipping below 20% at 20 mW/cm². The visible-blind performance makes these detectors potentially useful for measuring UV without the need for filters. Contact Fujun Zhang at [email protected].