A photoelectric system that converts light into charge and then stores the charge like a battery – a first for a single device – has been developed by researchers in China and Singapore. Made from layers of a 2D semiconductor and a transparent conductor held together by weak van der Waals interactions, the new device converts 93.8% of incident photons into electric current – far higher than the 50% typical for so-called “high performance” photoelectric devices – and can store charge for up to a week, making it suitable for applications in energy generation, photodetectors or light-based memory.
Van der Waals (vdW) heterojunctions like the one used here are a common feature in devices such as photovoltaic cells and photodetectors. Often made from p-n junctions, they work by absorbing photons that then create electron-hole pairs. The next step is to separate the electrons from the holes, which is usually done by applying a voltage. The problem is that these charge carriers rapidly recombine, shortening their lifetime and therefore limiting the device’s external quantum efficiency (EQE).