Integrated Organic Blue LED and Visible−Blind UV Photodetector

In this paper, we report on an integrated OLED−photodetector organic device using 3,6-dipyrenyl-N-hexylcarbazole (P2NHC) as the active layer. This device is an efficient blue emitter in forward bias and an efficient visible−blind UV photodetector in reverse bias. In forward bias, the device (as a blue emitter) has a low turn on voltage (2.7 V), a current efficiency of 2.0 cd/A for a brightness of 200−9000 cd/m2, and low droop at higher brightness. In reverse bias, the device has a saturated photoresponse of 77 mA/W at 390 nm, which corresponds to an internal quantum efficiency of 64%. The spectral response of a photodetector-only device indicated that carriers are generated in the interface of P2NHC/cathode. The singlet exciton diffusion length of P2NHC was determined to be 7.8 ± 1 nm, which is too small to account for the high photodetector efficiency. Alternate mechanisms are discussed to account for the high photodetector efficiency.