Synthesis of amphiphilic triblock fullerene derivatives and their solvent induced self assembly in organic solar cells

Two A-B-C type amphiphilic triblock fullerene derivatives (C 60 -PEHBS and C 60 -2EHTPB) were synthesized and applied to modify zinc oxide (ZnO) layer in inverted organic solar cells (OSCs). These two fullerene derivatives are typical hydrophilic-amphiphilic-hydrophobic triblock macromolecules with hydrophobic fullerene block, amphiphilic fluorene block and hydrophilic fluorene block. The amphiphilic fluorene contains 1,2-diethoxyethane (-C 6 H 14 O 2 ) on the side chains. And the hydrophilic fluorene blocks contain potassium butane-1-sulfonate (-C 4 H 9 SO 3 K) or N,N,N-trimethylpropan-1-aminium bromide (-C 6 H 16 BrN) side chains. When introducing as the cathode interface layers on ZnO, solvent annealing was applied on these two fullerene derivatives layers and then obvious self-assembly were observed, which were supported by X-ray diffraction (XRD) and water contact angle measurement. It was found that the fullerene derivatives could modify the nanoparticle of ZnO surface , passivate surface traps, suppress the recombination loss of carriers, reduce the series resistance and improve the electrical coupling of ZnO/active layer effectively. The power conversion efficiencies (PCEs) of the devices with structure of ITO/ZnO/fullerene derivatives/PTB7-Th: PC 71 BM/MoO 3 /Al are enhanced to 8.56% and 9.00% for C 60 -PEHBS and C 60 -2EHTPB respectively, compared to 8.13% of bare ZnO. The new amphiphilic triblock macromolecules and their solvent induced self-assembly opens an opportunity to study the morphologies in their super thin layers and develop their applications.