Enhancement of the air-stability and optimization of VOC by changing molecular conformation of polyelectrolytes

Three conjugated polyelectrolytes(CPEs) based on thiophene, thieno[3,2-b]thiophene, and 2,2'-bithiophene were designed and synthesized. The CPEs were successfully incorporated into polymer solar cells as pH-neutral hole-transporting layer(HTL) via solution process. The interfacial dipole and work function(WF) of CPE-coated ITO were controlled by the dipole moment of the polymer, which was in turn determined by the stereochemical properties of the molecular structure. CPE-coated ITOs showed sequentially stronger dipole moments due to an increase in the electrostatic repulsion in the molecules. The PCE of device with PFT as the HTL was maintained accompanied by 16% decrease when PEDOT:PSS-based device decreased over 50%.