Researchers from Helmholtz-Zentrum Berlin (HZB) and Potsdam University have reported perovskite–silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. Textured tandem devices have been presented before, aiming at improved optical performance, but optimizing film growth on surface-textured wafers has thus far remained challenging.
The research team showed a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enabled a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage was improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. The optically advanced rear reflector with a dielectric buffer layer resulted in reduced parasitic absorption at near-infrared wavelengths. As a result, the team achieved a certified power conversion efficiency of 29.80%.
"Our competences complement each other very well," says Prof. Dr. Christiane Becker, who developed the cell with the team led by Dr. Bernd Stannowski and Prof. Dr. Steve Albrecht. Becker's team introduced a nano-optical structure into the tandem cell: a gently corrugated nanotexture on the silicon surface.
"Most surprising, this texture brings several advantages at once: it reduces reflection losses and ensures a more regular perovskite film formation," says Becker. In addition, a dielectric buffer layer on the back of the silicon reduces parasitic absorption at near-infrared wavelengths.
The researchers concluded that customized nanotextures can help to improve perovskite semiconductor materials on diverse levels. These results are not only valuable for tandem solar cells made of perovskite and silicon, but also for perovskite-based light-emitting diodes (LEDs).