Efficient, bulk heterojunction organic photovoltaic cells based on boron subphthalocyanine chloride-C70

In this work, we describe the performance of organic photovoltaic cells (OPVs) based on the electron donor-acceptor pairing of boron subphthalocyanine chloride (SubPc) and C-70. As an acceptor, C-70 is a promising alternative to C-60 due to its red-shifted absorption edge and large extinction coefficient, permitting increased photocurrent generation. In uniformly mixed OPVs based on SubPc: C-70, peak power conversion efficiency is realized in devices containing 80 wt.% C-70. Further enhancement in device performance can be realized through the use of a continuously graded donor-acceptor heterojunction. The optimized graded heterojunction OPV shows a power conversion efficiency of eta(P) (5.4 +/- 0.2)% under simulated AM1.5G solar illumination at 100 mW/cm(2). This efficiency is significantly larger than the value of eta(P) (4.5 +/- 0.1)% realized using C-60 due to a substantial increase in the short-circuit current density. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737902]