Decoupling the optical and electrical properties of subphthalocyanine/C70 bi-layer organic photovoltaic devices: improved photocurrent while maintaining a high open-circuit voltage and fill factor

Abstract

We demonstrate a simple method for achieving high-performance subphthalocyanine (SubPc)/C₇₀ bi-layer organic photovoltaic (OPV) devices through the changing of the C₇₀ thickness. The optical and electrical properties of the OPV devices were decoupled and could be individually manipulated to obtain a significantly increased short-circuit current density (J_SC) without reducing the open-circuit voltage and the fill factor. The thickness-independent electrical property of the C₇₀ layer was systematically studied in terms of the dark currents of the OPV devices and the carrier mobilities of the organic layers; the results indicate that the considerable difference in mobility between SubPc and C₇₀ is not detrimental, while the optical-field distribution can be optimized by tuning the C₇₀ thickness. The power conversion efficiency was improved from 2.7 to 4.2% by optimizing the C₇₀ thickness. The optical effect upon the change in the C₇₀ thickness was thoroughly investigated by calculating the optical-field profile and the power dissipation inside the OPV devices on the basis of the transfer matrix method. The calculated results suggest that the optical-field intensity is insufficient in predicting the trend in J_SC. Instead, the power dissipation involving the absorption properties of materials and the optical-field distribution of OPV devices can provide deeper insight into the optical condition and indicates the importance of optimizing the film thickness in bi-layer OPV devices.