Regioselective 1,2,3-bisazfulleroid: Doubly N-bridged bisimino-PCBMs for polymer solar cells

The direct bisaddition of methyl 5-azido-5-phenylpentanoate to C₆₀takes place in the two neighboring pentagon-hexagon junctions of the same five-membered ring, yielding a regioselective bisazfulleroid, namely bisimino-PCBM. Because of its open annulene structure, this new bisheterofullerene is not only considered to be an isoelectronic analogue of pristine C₆₀, but also it is less symmetrical than previous reported mono-functionalized fullerenes, thereby displaying a stronger absorption in the visible region. The BHJ devices based on P3HT:bisimino-PCBM give a higher V_OCof 0.77 V relative to those using the PCBM in the literature, which can be attributed to the combination of the nature of the nitrogen atom and the open bridged mode in a fullerene cage. Furthermore, the bisimino-PCBM consisting exclusively of a doubly bridged open 11-membered ring with a hydroacenaphthylene perimeter is very new, therefore there is still plenty of room to establish better efficiencies of BHJ photovoltaic cells.