Designing thickness-insensitive cathode interlayers via constructing noncovalently conformational locks for highly efficient non-fullerene organic solar cells

Two novel water/alcohol-soluble conjugated polyelectrolytes, PF-TT and PF-BDT, were designed and synthesized as cathode interlayer (CIL) for highly efficient non-fullerene organic solar cells (OSCs). Both have superior charge transfer/transport capability owing to the intramolecular noncovalently conformational locks (NoCLs) formed through S & ctdot;H bonds between fluorene and thienothiophene (TT) or benzodithiophene (BDT) units along the polymer backbone. The intramolecular NoCLs make the molecular packing more compact and ordered. These beneficial effects on molecular conformation and stacking and their preferable face-on orientation significantly reduce the electrical transport resistance. They can also reduce the work function of a series of conducting materials (e.g., ITO, Ag and PEDOT:PSS) by generating strong interfacial dipoles through the pendant pyridine groups. Therefore, high power conversion efficiencies (PCEs) of 16.27%/17.83% and 17.09%/18.47% are obtained in PM6:Y6/PM6:BTP-eC9-based non-fullerene OSC devices when PF-TT and PF-BDT are used as CILs. Moreover, the device performance is quite tolerant to the thickness of the CILs. A prominent PCE value of 15.31% is still attained with a thickness of 53 nm for the PF-BDT layer. This PCE value stands out as one of the highest reported so far for organic CIL with a thickness surpassing 50 nm.