Structural and optical characterizations of pyronine B thin films and its photovoltaic applications

Abstract

In this work, the organic thin films of pyronine B (PYR.B) were deposited by thermal evaporation technique under high vacuum (∼10 4 Pa). The crystal structure, examined by X-ray powder diffraction, indicates that the films are single phase with strong preferred (4 0 0) orientation. Scanning electron micrographs of the films indicate a clearly almost uniform distribution with large grain sizes in the range 5–10 μm. The molecular structure and electronic transitions of PYR.B were investigated by Fourier-transform infrared (FTIR). Fluorescence characteristic of PYR.B at room temperature (300 K) exhibits visible band peak located at 569.65 nm. The color parameters were extracted from the reflectance spectrum of PYR.B. The optical constants such as refractive and extinction indices were determined from the measured transmittance and reflectance spectra using the spectrophotometric method. The dependence of absorption coefficient on the photon energy was determined and the analysis of the result showed that the optical transition in PYR.B is allowed and direct. The current density–voltage ( J– V) characteristics in dark show the rectification effect due to the formation of Schottky barrier at Al/PYR.B interface. The photovoltaic parameters were calculated from the J– V characteristics under illumination through ITO and discussed in detail.