Device Acts as Both Solar Cell and Battery
November 22, 2021
Photoelectric devices, which convert light energy into electricity, have a vital role in clean energy technologies. They often need to be coupled to batteries that store the captured energy, but researchers have now built a device that combines photoelectric charge generation with charge storage. The excited electrons can be retained for at least a week, until they are discharged as an electric current. The team says the device might find uses in energy generation, photodetectors, or light-based memories.
A good photoelectric device contributes a charge carrier to an electric current nearly every time it absorbs a photon; in other words, it has a high “external quantum efficiency” (EQE). The problem is that the negatively charged electron and the positively charged hole generated by a photon often recombine shortly after their creation. One way to increase the EQE of a device is to temporarily trap the charge carriers—at crystal defects, for example—before recombination can occur.
Yucheng Jiang of the Suzhou University of Science and Technology, China, and his co-workers set out to use this strategy in a device called a van der Waals heterojunction, in which two materials are held in contact by relatively weak van der Waals interactions. They used tungsten diselenide, a semiconducting material, and the transparent conductor strontium titanium oxide (STO). On the surface of the STO, the team produced a nearly two-dimensional “electron gas” (a state in which electrons move freely and independently) by employing a surface treatment. Using an electron gas as one component of such a heterojunction was new and led to the device’s novel properties.