Structural, optical, electrical and electronic properties of PEDOT: PSS thin films and their application in solar cells

The structural, optical, electrical and electronic properties of poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) thin films are investigated using transmittance spectrometry, atomic force microscopy, water droplet contact angle measurement, Raman scattering spectrometry, and photoelectron emission spectrometry. The fabrication parameters of the thin films were varied in order to determine which would improve the performance of the resultant PEDOT:PSS thin-film-based transparent conductive electrodes (TCEs) and hole-transporting materials (HTMs) in solar cells. For TCE applications, the experimental results lead to the conclusion that the necessary transparency and electrical conduc tivity of PEDOT:PSS (1:2.5 wt%) thin films can be simultaneously obtained by using a post-immersion treatment process which encourages the formation of connected conductive PEDOT channels and an increased carrier density in the PEDOT chains. On the other hand, the work function of the HTMs depends on the molecular structure of the PEDOT chains in the PEDOT:PSS thin films, which can be manipulated by varying the PEDOT/PSS ratio, spin rate, thermal anneal ing conditions and the viscosity of the PEDOT:PSS solutions. The work function of PEDOT:PSS thin films increases from 5.0 eV to 5.4 eV with an increase in the linearly oriented PEDOT chains, which results in an improvement in the open circuit voltage of the solar cells.