Visible-blind ultraviolet photo-detector using tris-(8-hydroxyquinoline) rare earth as acceptors and the effects of the bulk and interfacial exciplex emissions on the photo-responsivity

A visible-blind ultraviolet (VB-UV) photo-detector (PD) was demonstrated by using tris-(8-hydroxyquinoline) gadolinium (Gdq) as the electron acceptor (A), 1,3,5-tris(3-methylphenyl-phenylamino) triphenyamine (m-MTDATA) as the donor (D). For the comparison the PD diodes were also fabricated using other rare earth (RE)-q (REq) complexes (RE = Y, La, Eu, or Lu) as the acceptors. It is found that Gdq-PD diode with 1:1 ratio of m-MTDATA:Gdq offers a maximum photo-responsivity of 230 mA/W at −7.5 V bias. This result is markedly higher than inorganic counterparts and previously organic PD diode (30 mA/W) reported by Ray and Narasimhan [Appl. Phys. Lett. 91 (2007) 093516]. Moreover, the spectral response does not cover visible region. So high responsivity of Gdq-PD was attributed to the presence of dominant dissociation of the geminate carrier pairs at D:A intermolecular contacts. The improvement is the results of the lowest exciplex- and bulk-emissions among the REq-PD diodes and in the various ratio of D:A blend, more detail mechanism was also discussed. Besides degradation tests of the Gdq-PD diode under UV and fluorescent lamp show that the UV detector can suffer from the application conditions.