Quinonoid Zwitterion: an Amphiphilic Cathode Interlayer with Initial Thickness-Insensitive and Self-Organizing Properties for Inverted Polymer Solar Cells.

Orthogonal solvent processability is generally considered one of the key requirements for an efficient interfacial material. Here we showed that in inverted polymer solar cells (PSCs), solvent orthogonality is not required for an effective and reliable cathode interlayer. A quinonoid zwitterionic molecule with amphiphilic property (dissolved in both methanol and o-dichlorobenzene (o-DCB)) named ZW-Bu was first applied as the cathode interlayer in the inverted PSCs. For three different photoactive systems, the devices with ZW-Bu CBL exhibited better performance than those with commonly used ZnO CBL. Most importantly, the device efficiency was fairly insensitive to the initial thickness of ZW-Bu. In addition, due to the high surface energy of ZW-Bu film, it was successfully used as self-organized CBL in P3HT:PC61BM system, yielding a desirable efficiency compared to the PSCs fabricated via layer-by-layer deposition method.