Photoelectrochemical Energy Storage with Organic Solar Cells

The global trend towards automatization and miniaturization of smart devices has triggered the development of reliable off-grid power sources with low economic and environmental impact. Such autonomy can be provided when a photovoltaic cell is integrated with an electrochemical storage device in one monolithic device. This work demonstrates a reliable and straightforward approach to monolithically integrate high-performance single and multijunction organic solar cells with mesoporous nitrogen doped carbon nanosphere-based supercapacitors or lithium-organic batteries in a single device with a three-electrode configuration. To assess the efficiency of these devices, a novel approach is presented that relies on the direct monitoring of both integrating parts during illuminated and dark phases and accounts for possible losses. This versatile approach is applicable for all kinds of integrated multifunctional photoconversion-storage systems. For the photosupercapacitors, the evaluation with the standard literature approach showed an outstanding performance with a peak photoelectrochemical energy conversion efficiency of 17 %. However, in our opinion this type of efficiency does not properly represent the real overall device efficiency. Based on our newly developed efficiency determination, a more modest overall cycle efficiency of 2 % is obtained. For battery-based devices, a higher output voltage is achieved, but at the cost of a lower, 0.3% cycle efficiency. In our view these values represent the real overall performance of the integrated device in a precise manner and will thus enable meaningful direct comparisons among different photoelectrochemical storage systems.