The effects of the temperature and the presence of an interfacial buffer layer on the nanostructure of organic bulk heterojunctions (BHJs) based on copper phthalocyanine (CuPc) and fullerene (C60) systems were examined using real-time in situ X-ray measurements. The CuPc:C60 BHJ structures prepared without a buffer layer formed a standing-on configured gamma-CuPc phase. Once formed, the gamma-phase could be rendered thermally stable by post-annealing at 180 degrees C. The insertion of a CuI buffer layer prior to the deposition of a CuPc:C60 BHJ layer induced the formation of a lying-down configured CuPc phase in the BHJ layer. The CuPc peak intensity and lattice parameters gradually increased upon thermal annealing. This increase in intensity appeared to be related to the strain at the interface between the CuPc:C60 and CuI layers. (C) 2014 Elsevier Ltd. All rights reserved.