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

Abstract

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 wavelengths 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/cm2 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.