Design of broadband transparent electrodes for flexible organic solar cells

Broadband transparent electrodes, Ta2O5/Ag/WO3−x, are successfully designed to enhance light absorption and carrier transport properties in organic solar cells (OSCs) as an alternative to ITO/PEDOT:PSS. Employing the optical constant matching layer, zero reflection conditions could be achieved over a broad range of wavelengths. Moreover, the non-stoichiometric WO3−x could induce a large density of gap states near the Fermi level via quick thermal deposition, acting as the transport path of carriers. Significantly improved current densities were achieved, increasing the power conversion efficiency from 2.1% to 2.9%, values which are comparable to conventionally fabricated devices on ITO/PEDOT:PSS.