Sulfonate anionic small molecule as a cathode interfacial material for highly efficient polymer solar cells

The cathode interlayer is essential to bulk heterojunction polymer solar cells (PSCs). As we all know, most of the organic interfacial materials are amino derivatives, including neutral amine derivatives and ammonium derivatives. Herein, a non-amino small molecule, TBT-a, with sulfonate anionic pendants was synthesized and interface modification was investigated. The PSC with TBT-a as the cathode interlayer exhibited a high power conversion efficiency of 8.68%. We found that the TBT-a interlayer simultaneously enhanced all the device parameters, probably by inducing an effective interface dipole, altering the optical distribution, and enhancing the electron mobility. These results indicated that sulfonate interfacial materials could play a similar role as amine-based interfacial materials in interface modification.