Influence of the terrace width of pentacene underlayers on the crystallinity of C60 overlayers

Abstract

Pentacene and fullerene (C60) form an efficient stacked heterostructure in organic solar cells, and C60 films exhibit high crystallinity on pentacene films. However, the mechanism of the crystallinity improvement in C60 overlayers remains to be fully elucidated. In this work, the surface (step and terrace structure) of pentacene films is investigated in terms of the terrace width using atomic force microscopy (AFM) to clarify the mechanism. We found that the terrace width becomes wider as the substrate temperature for pentacene film growth increases, and the terrace width becomes narrower as the thickness of pentacene films increases. In addition, we investigate the influence of the terrace width of pentacene underlayers on C60 overlayers using AFM and X-ray diffraction. We found that pentacene underlayers with wide terraces increase the grain size and improve the crystallinity of C60 overlayers. These findings indicate that growing pentacene underlayers with wider terraces allows for further enhancement in the crystallinity of C60 overlayers, leading to higher quality pentacene/C60 stacked heterostructures.