Hydroxymethyl Functionalized PEDOT-MeOH:PSS for Perovskite Solar Cells.

A hole transport material poly(hydroxymethylated-3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT-MeOH:PSS) are synthesized using the oxidative chemical polymerization method and deployed in inverted p-i-n MAPbI3 perovskite solar cells (PVSCs). By introducing a hydroxymethyl (-MeOH) function group to the oxyethylene ring of EDOT, it lowers the highest occupied molecular orbital of PEDOT-MeOH and thus increases the work function of PEDOT-MeOH:PSS. In addition, the -MeOH function group allows the formation of hydrogen bonding among EDOT-MeOH monomers and with sulfate groups on PSS, promoting the growth of long chain PEDOT-MeOH and enhancing the PSS doping efficiency. The work function and conductivity of PEDOT-MeOH:PSS are 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 overperform 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.