High-Performance Ta2O5/Al-Doped Ag Electrode for Resonant Light Harvesting in Efficient Organic Solar Cells

A efficient indium tin oxide (ITO)-free transparent electrode based on an improved Ag film is designed by introducing small amount of Al during co-deposition, producing ultrathin and smooth Ag film with low loss. A transparent electrode as thin as 4 nm is achieved by depositing the film on top of Ta2O5 layer, and organic solar cells based on such ultrathin electrode are built, producing power conversion efficiency over 7%. The device efficiency can be optimized by simply tuning Ta2O5 layer thickness external to the organic photovoltaic (OPV) structure to create an optical cavity resonance inside the photoactive layer. Therefore Ta2O5/Al-doped Ag films function as a high-performance electrode with high transparency, low resistance, improved photon management capability and mechanical flexibility.