Enhanced Open‐Circuit Voltage in High Performance Polymer/Fullerene Bulk‐Heterojunction Solar Cells by Cathode Modification with a C₆₀ Surfactant

A bis-adduct C60 surfactant is used to modify the energy-level alignment at the interface between the photoactive layer and cathode contact of a conventional bulk-heterojunction solar cell comprised of a low-bandgap polymer and PC71BM. The metal Fermi level pins to that of the surfactant, dramatically increasing the device's open-circuit voltage regardless of the cathode metal identity, leading to significantly enhanced power-conversion efficiency (up to 6.22%) and device stability.