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 η P (5.4 ± 0.2) under simulated AM1.5 G solar illumination at 100 mW/cm 2. This efficiency is significantly larger than the value of η P (4.5 ± 0.1) realized using C 60 due to a substantial increase in the short-circuit current density.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation MRSEC Program under Award Number DMR-0819885 and University of Minnesota Initiative for Renewable Energy and the Environment. R.P. also acknowledges support from a University of Minnesota Doctoral Dissertation Fellowship.