Nonionic fluorosurfactant as a cathode interfacial layer for organic solar cells

Nonionic fluorosurfactants (NFSs) were first used as the cathode interfacial layer (CIL) of organic solar cells (OSCs). Commercially available NFSs, FS-31, and Zonyl FS-300 possess both hydrophilic part of ethylene glycol chains and hydrophobic part of fluoroalkyl chains, which endows NFSs with amphiphilic nature and thus significantly improves processability regardless of underlying surface conditions. In addition, NFSs spontaneously forms an interfacial dipole layer at the cathode interface to reduce the energetic barrier between the photoactive layer and cathode. The strength of the dipole moment is affected by the ratio of carbon to fluorine in the molecular structure of NFSs. Benefiting from the improved anode contact properties, the OSCs with high performing fullerene-based photoactive materials and NFS CILs exhibited high-power conversion efficiency of 9.1%, which is higher than that of the devices without CIL (6.6%).