CuPc/C60 bulk heterojunction photovoltaic cells with evidence of phase segregation

This work presents organic photovoltaic (OPV) device study based on cupper phthalocyanine (CuPc) and fullerene (C60) bulk heterojunction (BHJ) structure. By varying blend composition, the optimized performances were obtained in 75%-CuPc containing devices with anode buffer of either CuPc or HPCzI (1,3,4,5,6,7-hexaphenyl-2-{3'-(9-ethylcarbazolyl)}isoindole). It was discovered by scanning electron microscopy that 75%-CuPc containing film possessed phase separation, which is beneficial to charge transport via percolation process. Additionally, electronic absorption measurement and hole only device study showed that, depending on the mixing ratio, the absorption and the hole transport ability were different. The blend film containing 75% CuPc had the largest integrated absorption with the most CuPc dimmer aggregate and the least C60 aggregate. Moreover, the 75% CuPc blend film also possessed the highest hole transport ability. Thus, the best performance of the 75% CuPc BHJ device is mainly attributed to its good carrier transport originating from phase segregation. The present work highlights the phase separation in CuPc:C60 mixing film with optimized ratio, as well as its corresponding electronic absorption and carrier transport properties, which are essential for OPV device performance. Hence, insights are inferred for further engineering of BHJ OPV devices based on small molecules. (C) 2012 Elsevier B.V. All rights reserved.