Search

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 (JSC) 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 JSC. 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.

Transparent organic upconversion devices are shown in a night-vision demonstration of a real object under near-infrared (NIR) illumination in the dark. An extraordinarily high current gain - reflecting the on-off switching effect - greater than 15 000 at a driving voltage of 3 V is demonstrated, indicating the high sensitivity to NIR light and potential of using the proposed upconverter in practical applications. A maximum luminance exceeding 1500 cd m(-2) at 7 V is achieved. Unlike previous studies, where 2D aperture projection is reported, the current study shows 3D images of real objects under NIR illumination in the dark.