A planar heterojunction organic solar cell (OSC) with high internal quantum efficiency (IQE=95.6% at 590 nm) was demonstrated based on boron subphthalocyanine chloride (SubPc) and C-60 as the electron donor and acceptor materials. A thin layer of N,N-dicarbazolyl-3,5-benzene (mCP), acting as an electron and exciton blocking layer, was inserted between the ITO anode and the SubPc layer to prevent leakage current and exciton quenching. In the optimized device, a mCP thickness of 3 nm was thick enough to block the excitons (as suggested by a high IQE and longer-lived photoluminescence), resulting in an open circuit voltage of 1.09 V. a short circuit current of 7.87 mA/cm(2), a fill factor of 59, and a power conversion efficiency of 5.08%. Increasing the mCP thickness resulted in increased serial resistance and SubPc crystallization that reduced the fill factor, V-oc, and J(sc). Due to the narrow absorption band of SubPC (71 nm at the full-width-at-half-maximum), this high performance (both in peak IQE and V-oc) device has the potential to be used as a subcell in a spectral splitting solar cell module. (C) 2013 Elsevier B.V. All rights reserved.