Micro-Raman study on electrochemistry in multilayer devices consisting of organic thin films and control of their properties

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We have studied the micro-Raman spectra of single-layer or multilayer devices consisting of thin films of organic materials (NPD, CBP, copper phthalocyanine (CuPc), Alq_3, pentacene, PTCDI derivatives, PEDOT-PSS, etc.) by using 532, 633, and 830 nm laser lines. We have observed the Raman spectra of organic light-emitting diodes under operation. We have obtained the following information about organic thin films. (1) We have determined the molecular orientations of pentacene, CuPc, PTCDI derivatives, which are related with the performance of organic thin-film transistors. (2) We have found the Raman markers of crystalline/amorphous states of hole transport materials such as NPD of organic light emitting diodes. (3) We have determined the temperatures of CuPc and PEDOT-PSS layers under operation by measuring Stokes and anti-Stokes Raman scattering. (4) We have observed the dedoping of PEDOT chains in polymer light-emitting diodes upon operation. Probably, the reduction of the PEDOT chains (dedoping) is most likely one of the intrinsic factors of the degradation of the devices. (5) We have observed Raman bands due to Alq_3 for a metal-insulator-semiconductor device having the structure of n-Si/SiO_2/A1q_3/Au thin film. The intensities of these bands have been enhanced by the surface enhanced Raman scattering effect. We have observed Raman spectral changes induced by hole injection into the Alq_3 layer. Thus, Alq3 is unstable for holes, which is one of intrinsic factors of device degradation. We have demonstrated that micro-Raman spectroscopy is a powerful tool for the researches of organic light-emitting diodes and transistors.