Optical properties of P- type polypyrrole thin film synthesized by pulse laser deposition technique: Hole transport layer in electroluminescence devices

Defect free, high-quality P-type Polypyrrole (PPy) thin film was deposited on ITO substrate at 150 degrees C by Pulse Laser deposition (PLD) technique. Fourier Transform Infrared spectroscopy (FTIR) confirmed the PPy formation as a thin film without any cleavage in the functional group. A lower shift in vibration mode was observed for PPy thin film when compared to PPy powder confirming higher conductivity in both polarons and bipolarons region. Morphology of the thin film was uniform and smooth which was revealed by Scanning electron microscopy (SEM). Optical properties were studied systematically. 59.7% transmittance and lower band gap of 1.73 eV was observed for the thin film. The optical conductivity of the PPy thin film was 0.27 S/cm. Dielectric properties of the PPy thin film were investigated in detail. Room temperature photoluminescence spectra for PPy thin film exhibited three peaks at 373 nm, 425 nm, and 486 nm which was due to pi ->pi* electronic transitions, polarons and bipolarons respectively. Higher luminescence efficiencies of PPy thin film can be used as good hole transport layer [HTL] in electroluminescence devices.