The effect of a thin pentacene anode buffer layer on the performance of small-molecule organic solar cells (OSCs) was experimentally investigated primarily from morphological and crystallographic viewpoints. The OSC had a structure of indium-tin oxide (ITO, anode)/pentacene (anode buffer)/copper phthalocyanine (CuPc, donor)/fullerene (acceptor)/bathocuproine (cathode buffer)/Ag (cathode). The thin pentacene layer provided an enhanced initial device performance, that is, an increase of 5-29% in the short-circuit current density, resulting in an increase of 10-43% in the power conversion efficiency eta(p). Atomic force microscopy showed that the roughness of the pentacene surface was large and that this roughness was increased and transferred to the overlaid CuPc surface. X-ray diffraction and near-edge X-ray absorption fine structure spectroscopy analyses showed that the standing-up CuPc crystallite orientation became randomized as the pentacene thickness was increased. The pentacene layer did not bring about the lying-down configuration of CuPc film molecules with respect to the substrate surface. The origin of the increase in eta(p) was the increase in the area between the donor-acceptor interface with enhanced roughness, which brought about an increase in the number of carriers generated at the interface. The reduction of energy barrier height for hole extraction from CuPc to ITO was also a possible reason for the increase in eta(p).