Tuning Work Function and Conductivity of Methylhydroxyl Functionalized PEDOT-MeOH:PSS as a Hole Transport Material for Perovskite Solar Cells

Abstract

A hole transport material poly(hydroxymethylated-3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT-MeOH:PSS) was synthesized using the oxidative chemical polymerization method and deployed in inverted p-i-n MAPbI3 perovskite solar cells (PVSCs). By introducing a methylhydroxyl (-MeOH) function group to the oxyethylene ring of EDOT, it lowers the highest unoccupied molecular orbital of PEDOT-MeOH. In addition, the MeOH function group allows the formation of hydrogen bonds among EDOT-MeOH monomers and with sulfate groups on PSS, promoting the growth of long chain PEDOT-MeOH and enhancing the doping efficiency. The work function and conductivity of PEDOT-MeOH:PSS were tuned via varying the amount of PSS and ferric oxidizing agent used in the polymerization and further via adding ethylene glycol as the secondary doping. The optimized PEDOT-MeOH:PSS-based PVSCs overperformed the PEDOT-PSS-based PVSCs because of better aligned energy level and enhanced conductivity of PEDOT-MeOH:PSS. This work provides new insights on developing hole transport materials to enable efficient inverted p-i-n PVSCs.