Could dye-sensitised solar cells work in the dark?

Chinese researchers believe they’ve gotten a step closer to producing all-weather photovoltaics by integrating phosphors into solar cells

Solar power is playing an ever-greater role in our energy landscape, and its efficiency continues to improve. However, to date, photovoltaic systems can still only produce power when the sun is in the sky. But a group of materials scientists in China say that they’ve found a way to help dye-sensitised solar cells work after dusk.

All photovoltaic devices are based light absorption followed by charge separation. In most commercial devices, solid-state silicon manages both of these tasks, but in dye-sensitised solar cells (DSSCs), sometimes called Grätzel cells, the two tasks are separated. In their thin film structure, light is absorbed by a sensitizer electrolyte (a dye), with charge separation then occurring at the interface between the dye and a solid, mesoporous oxide layer. Into this structure, Qunwei Tang and his colleagues at the Ocean University of China propose adding long persistence phosphors, in order to utilise unabsorbed light in the cell.

Writing in Nano Energy [DOI: 10.1016/j.nanoen.2017.01.047], they report on the integration of purple, blue, cyan, green, red and white-emitting phosphors into dye-sensitised solar cells with TiO2 photoanodes. The idea is that the phosphors act as storage materials within the cell – when illuminated by sunlight, they harvest energy from ultraviolet light, and then, once the light source is removed, they release persistent visible fluorescence at a different wavelength that can then be absorbed by the dye.

And it appeared to work largely as predicted. The authors showed that when illuminated by a solar simulator, the standard DSSC displayed a cell efficiency of 8.08%, while the cell with a green phosphor reached 10.08%. In dark conditions, the voltage output of the standard cell rapidly dropped to zero. But the phosphor-enhanced cells continued to produce small voltages in the absence of light. Though all displayed a significant reduction in the first five minutes of darkness, five of them persisted, with the cyan cell producing 0.284 Voc one hour after the light source had been switched off.

While still very much at the lab scale, this result poses further questions of current DSSC design. The same group recently reported on their development of a flexible cell that can be triggered by both rain and sun. Combined with this latest paper, they seem to be getting closer to their goal of making a truly all-weather photovoltaic.

This story originally appeared here:

Original research paper: Q. Tang, J. Wang, B. He, P. Yang, “Can dye-sensitized solar cells generate electricity in the dark?” Nano Energy, Vol 33 (2017) 266–271. DOI: 10.1016/j.nanoen.2017.01.047
OpenGraph description (100 chars): Solar panels that generate electricity after sunset may be a step closer