Study of organic visible-blind photodetector based on Alq3:NPD blend for application in near-ultraviolet detection

In this paper, we present a visible-blind organic photodetector with high sensitivity to the UV rays. The active layer is a bulk heterojunction of a binary blend of tris(8-hydroxyquinoline) aluminum (Alq3) as an acceptor material along with N, N'-Di [(1-naphthyl)-N, N ' diphenyl]-(1, 1'-biphenyl)-4, 4'-diamine (NPD) as a donor material. The device was fabricated using simple solution processing method with structure of ITO/PEDOT:PSS/ Alq3:NPD/LiF/Al. The optical characteristics of the crystalline film is completely transparent at visible wave-lengths and absorbs light at UV frequencies. Moreover, it exhibits emission quenching of photoluminescence intensity when more Alq3 added i.e. 2, 3 and 4 with respect to the host. In the electrical characterization, the optimized device (2:1 blend ratio) exhibits high sensitivity of 25,300 at -2 applied bias and under illumination of 40 mW/cm(2) UV light. Response and recovery times of the UV sensor was found to be 0.69 s and 0.36 s, respectively. The result indicates that the blend of Alq3/NPD with its high photosensitivity and fast response to the UV light of 365 nm wavelength can be employed in the fabrication of a cost-effective and highly sensitive UV photodetector.