Absorbing Visible Light Materials of Subphthalocyanine and C₇₀for Efficient Planar-Mixed Organic Photovoltaic Devices

Abstract

The authors report on a highly efficient small-molecule organic photovoltaic device employing a planar-mixed heterojunction structure with subphthalocyanine (SubPc) as the donor and C70 as the acceptor. By changing the mixing ratio of SubPc and C70, the power conversion efficiency can be significantly improved from 1.8% to 6.0% under air mass 1.5 G solar illumination. From the internal quantum efficiency measurement, the highest carrier extraction is observed when an optimized weight ratio for SubPc to C70 of 1:7 is used. Besides, atomic force microscopy images demonstrate that a good phase separation of the blend layer is realized under such an optimized mixing ratio. This phenomenon may contribute to the improved fill factor and hence the bulk resistance. As a result, the JSC of our device is significantly enhanced to 13.0 mA/cm2, which is almost twice the conventional value for planar heterojunction SubPc devices.