Activating π‐Electron Conjugated Networks of Self‐Assembled Multilayers for 21.1% Efficiency Organic Solar Cells

Self-assembled monolayers suffer from the insufficient electrical conductivity, stemming from their ultrathin nature and disordered molecular orientation. Here we report a π-skeleton unit of 3,6-dibenzothiophen-9H-carbazol to building a self-assembled multilayer (SAMUL) that exhibits superior carrier transport and outstanding resistance to external stimuli. The π-expanded skeleton effectively enhanced the molecular crystallinity and face-on orientation, which successfully activated a large π-electron conjugated network within SAMULs. This conjugated network structure greatly broadens the delocalization region of free radicals, which not only significantly enhances the electrical conductance and hole-transporting capability, but also reinforces the photochemical stability. Consequently, a record-high efficiency of 21.13% (certified as 20.77%) with a notable fill factor of 83.48% was achieved for binary organic solar cells. This work provides a new inspiration for the molecular skeleton design in organic electronics.