Application of the thermally stimulated current method to prove the Gaussian distribution of the charge transport and trapping states in the band gap of MDMO-PPV, depending on the synthesis route

Abstract

We had investigated energetical distribution of the charge trapping states in MDMO-PPV ([poly-(2-methoxyl), 5-(3,77dimethyloctyloxy)] paraphenylenevinylene) by the thermally stimulated current measurements. The method was chosen because it is a direct photoelectrical method directly related with the charge carrier transport and trapping in materials with defect states. We have demonstrated possibilities of the selective filling of the trapping states by the light with different spectral regions below and above the band gap. Such procedure followed by the numerical fitting enabled assessing of the Gaussian distribution of the trapping states in the band gap. The sensitivity of the technique is evidenced by the results of the analysis, demonstrating that in MDMO-PPV synthesized by different routes – Gilch and Sulfinyl – different defect states were identified. In the material synthesized in the Gilch route distributed trapping states are located at 0.22 and 0.40eV, meanwhile synthesis in the Sulfinyl route resulted in the appearance of the traps at 0.28eV.