Raman and infrared spectroscopy of organic electronic devices

We present Raman and infrared studies on the structures of organic semiconductor thin films used for electronic devices. The Raman spectra of crystalline and amorphous states of an organic semiconductor, N,N′-di-1-naphthaleyl-N,N′-diphenyl-1,1′-biphenyl-4, 4′-diamine (NPD), were measured. These states give rise to slightly different peak positions and widths of each Raman band. Raman images were observed for polycrystalline pentacene films evaporated on a silicon substrate. The structural defects were found in the images of the intensity ratio I ₁₅₉₆/I₁₅₃₃, which reflects the orientation of molecules i.e., crystalline domains. Photoinduced infrared absorption from the composite of regioregular poly(3-dodecylthiphene) and C₆₀ was measured by the difference FT-IR method. The observed absorption is attributable to photogenerated carriers. The action spectra of photoinduced infrared absorption are explained by electron transfer from photogenerated excited states on a polymer chain to C₆₀.