Triphenylamine-Based Plasticizer in Controlling Traps and Photorefractivity Enhancement

Abstract

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 highperformance, 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.

Photoelectron Yield Spectroscopy and Transient Photocurrent Analysis for Triphenylamine-Based Photorefractive Polymer Composites

“…In a previous report [17], we measured a photocurrent of 4.2 µA for PDAA/TPAOH/ 7-DCST/PCBM and 0.036 µA for PDAA/TAA/7-DCST/PCBM at E = 40 V µm −1 . To determine the significant difference in the photocurrent between PDAA/TPAOH/7-DCST/ PCBM and PDAA/TAA/7-DCST/PCBM, the role of TPAOH and TAA should be clarified in photorefractive composites.…”

“…Obtained PR composite was pressed between indium-tin-oxide (ITO)-coated glass plates to prepare the PR composite sample film. The structural formulas for the compounds and the details for the preparation of the PDAA-based polymers are shown in previous papers [17]. The thickness of the sample film was 50 µm.…”

“…The difference in the photorefractive performance of PDAA/TAA/7-DCST/PCBM and PDAA/TPAOH/7-DCST/PCBM in terms of the optical diffraction and the response time are discussed from the aspect of trapping behavior. The photorefractive quantities of diffraction efficiency and response time reported previously [17] are summarized in Table 1. The optical diffraction efficiency for both polymers is comparable, but the response time τ of 8 ms for PDAA/TPAOH/ 7-DCST/PCBM is faster than that of 67 ms for PDAA/TAA/7-DCST/PCBM.…”

“…Quantitative analysis of the transient photocurrent has been carried out for poly(4-diphenylamino) styrene (PDAS)-based PR polymers using a two-trap model [15]. Transient photocurrents were reported for poly(4-(diphenylamino)benzyl acrylate) (PDAA)-based PR polymers [16,17]. In particular, a significant difference in the photocurrent of two orders of magnitude has been reported for PDAA PR composites with different photoconductive plasticizers, (4-(diphenylamino)phenyl)methanol (TPAOH) and (2,4,6-trimethylphenyl)diphenylamine (TAA) [17].…”

“…Transient photocurrents were reported for poly(4-(diphenylamino)benzyl acrylate) (PDAA)-based PR polymers [16,17]. In particular, a significant difference in the photocurrent of two orders of magnitude has been reported for PDAA PR composites with different photoconductive plasticizers, (4-(diphenylamino)phenyl)methanol (TPAOH) and (2,4,6-trimethylphenyl)diphenylamine (TAA) [17]. However, a detailed analysis of the photocurrent in PDAA PR composites has not yet been performed.…”