@@@@Highlights •Designed GQDs are applied at PEDOT:PSS/PVK interface to modulate the energy level and charge transfer simultaneously.•N,Cl-GQDs regulate the interface charge distribution and passivate the defects, guaranteeing efficient charge transport.•Sn-Pb based PSCs achieve impressive efficiency of 21.5%, which are among the best parameters in reported low bandgap-PSCs.