Triphenylamine-Based Plasticizer in Controlling Traps and Photorefractivity Enhancement

A video rate operation (30 Hz) with more than 80% diffraction efficiency and net gain of 89 cm–1 was reported in a photorefractive (PR) composite based on poly((4-diphenylamino)benzyl acrylate) (PDAA). A diffraction efficiency of 60% was attained at 60 Hz. To reveal the mechanism behind such high-performance, transient photocurrent measurements were performed. The investigation clearly showed the importance of the (4-(diphenylamino)phenyl)methanol (TPAOH) plasticizer in the charge transport process of the PR composite. The function of TPAOH was demonstrated as a normal plasticizer, as well as an effective photoconductivity enhancement factor of the composite. The analysis of the shapes of the transient photocurrent curve with two trapping sites revealed that TPAOH strongly assisted charge transport in PDAA. The response time of the PR composite was improved by increasing the TPAOH concentration and suppressing the shallow trapping effect. In contrast, the reference 2,4,6-trimethyl-N,N-diphenylaniline (TAA) plasticizer was found to significantly suppress the photocurrent (up to 100 times) compared to that of the TPAOH samples. The replacement of TPAOH by TAA degraded the response time of the diffraction beam. This was attributed to the low-scattering effect caused by the TAA. The study revealed that the deep and shallow traps originate from the PDAA polymer.