Electrical and optical characterization of photooxidized TPD

Abstract

Changes in current–voltage characteristics of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′diamine (TPD) dispersed in polymer films are studied when solutions of TPD are exposed to UV light. Higher current density is observed in films cast with solutions exposed under UV for an optimum time. Observations are rationalized on the basis of the photoinduced oxidation of TPD when chlorinated solvents are used. Photoinduced generation of the TPD cation (TPD⁺) is confirmed using linear absorption spectroscopy when compared with salt-based generation (using CuCl₂) of TPD⁺. Results suggest another possible route for generating TPD⁺ and the possibility of unintentional oxidation of TPD when chlorinated solvents like chloroform or dichloromethane are used for making devices.