Self-Assembled Conjugated Polyelectrolyte-Ionic Liquid Crystal Complex as an Inter layer for Polymer Solar Cells: Achieving Performance Enhancement via Rapid Liquid Crystal-Induced Dipole Orientation

A simple approach was demonstrated to manipulate dipole moment of interlayer in polymer solar cells (PSCs). The ionic liquid crystals (ILCs) 3-((2'-(4 ''-cyanobiphenyl-4-yloxy)ethyl)dimethylammonio)propanesulfonate (CbpNSO) with zwitterionic charges were blended with cationic conjugated polyelectrolyte (CPE) poly[3-(6-trimethylammoniumhexyl)thiophene] (PTNBr) to afford a novel CPE-ILC complex. The water/alcohol solubility of the CPE-ILC complex enables it to be green solvent processable. The spontaneous orientation of liquid crystal (LC) favors more ordered structural arrangement in CPE-ILC complexes. More importantly, LC-assistant assembly improves the orientation of dipole at cathode and significantly reduces the work function of ITO. The power conversion efficiency (PCE) of P3HT:PC60BM-based inverted PSCs with the layer of PTNBr CbpNSO is increased by 37% with respect to that of the device with pure PTNBr. Incorporation of PTNBr CbpNSO into the devices based on PBDTTT-C-T and PC71BM affords a notable PCE of 7.49%. It should be noted that mesogens reduce the activation energy of molecular reorganization and accelerate dipole orientation in CPE-ILC interlayer under external electric field, which enables the dipole of this interlayer can be readily manipulated. Because of the rapid orientation of the dipole, PTNBr CbpNSO shows reversible dipole at the active layer/ITO interface during the reversible bias process.