This study investigates the effect of substrate temperature (T-s) on the boron subphthalocyanine chloride (SubPc) thin film and its power conversion efficiency in SubPc/C-60 heterojunction photovoltaic cells. The orientations of SubPc molecules in thin films determined by X-ray diffraction is strongly correlated with the electronic properties of the organic thin films, and can be controlled by the substrate temperature during the vapor deposition. An optimal substrate temperature of 120 degrees C has been concluded to induced (221) molecular orientation over the (122) orientation and significantly improve the carrier transport of the SubPc thin film. A SubPc/C-60 heterojunction photovoltaic cells thus fabricated shows higher open-circuit voltage and up to 1.55% conversion efficiency has been achieved, which is attributed to preferential (221) orientation of the SubPc deposited at the elevated temperature. (C) 2011 Elsevier B.V. All rights reserved.