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

Abstract 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.