Atmospheric-pressure argon plasma etching of spin-coated 3,4-polyethylenedioxythiophene:polystyrenesulfonic acid (PEDOT:PSS) films for cupper phtalocyanine (CuPc)/C60 heterojunction thin-film solar cells

Depth profiles of the optical constants, carrier mobility, and carrier density of spin-coated 3,4-polyethylenedioxythiophene:polystyrenesulfonic acid (PEDOT:PSS) films were investigated by real-time characterization by the spectroscopic ellipsometry (SE) during argon plasma etching at atmospheric pressure. Spectral analysis revealed that homogeneous etching occurred within 10–15 nm of the top surface, followed by the appearance of a conductive PEDOT phase and surface roughning, which originated from the depth profile of the PEDOT-to-PSS molar concentration ratio. The use of the plasma-etched PEDOT:PSS layer improved relatively the performance of the copper phtalocyanine (CuPc)/C60 organic thin-films solar cells as a hole-transport layer with higher optical transmittance by adjusting the plasma etching condition.