Infrared and Raman spectroscopy of organic thin films used for electronic devices

We present Raman imaging and photoexcitation infrared studies of organic semiconductor films, which are used in organic light-emitting diodes, thin-film transistors, and photovoltaic solar cells. Raman images of the ratio (R) of intensity of the 1596-cm−1 band (b3g) to that of the 1533-cm−1 band (ag) were used for characterizing the 1.55-nm and the 1.44-nm phases in pentacene thin films. The Raman spectrum of N,N′-di-1-naphthaleyl-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPD) film formed on a MoO3-deposited indium–tin-oxide (ITO)/glass substrate indicated that the cation of NPD is formed upon oxidation by MoO3. The Raman image of the sample showed the heterogeneous distribution of the cation of NPD. Photoinduced infrared absorption from a film of regioregular poly(3-octylthiophene) (P3OT) and [6,6]-phenyl-C61-butyric acid methyl ether (PCBM) blend was measured by difference infrared spectroscopy. The temperature dependence of photoinduced infrared absorption due to positive polarons showed the existence of two kinds of carrier traps.