An investigation of design principles toward near infrared organic upconversion devices

Among the reported Near-infrared (NIR) Organic upconversion devices (OUDs), the devices realized by utilizing NIR sensitive bulk heterojuntion (BHJ) as sensitizers and normal OLED as emitters have been demonstrated as the most typical structure which exhibited higher photon-to-photon conversion efficiency than other OUDs. In this paper, NIR OUDs by integrating lead phthalocyanine (PbPc):C60 BHJ as sensitizer with normal OLED and inverted OLED as emitter were both fabricated and studied. And the impact of carrier blocking layers on the performance of the devices were investigated. Especially for OUDs based on inverted OLED, MoO3 as buffer layer, copper phthalocyanine (CuPc) and 1, 4-bis(1-naphthylphenylamino) biphenyl (NPB) as electron blocking layer (EBL) was inserted between the ITO cathode and the BHJ sensitizer, respectively. It was demonstrated that OUDs with CuPc EBL exhibited best performance, which signified that the performance of the devices can be effectively improved via introducing an electron blocking layer with high hole mobility. Moreover, the brightness and pixel-less imaging capability of both types OUDs dependent on applied voltages in the dark and under illumination were investigated.