German researchers achieve 25.5% efficiency for perovskite tandem solar cells

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Researchers from Berlin’s Helmholtz Zentrum (HBZ) Research Institute have developed a perovskite-silicon tandem solar cell with an efficiency of 25.5%.

According to the research team, a silicon layer was etched on the back-side of the cell, while the perovskite layer was applied by spincoating onto the smooth front-side of the silicon. By applying a a polymer light management (LM) foil to the front-side of the device, the scientists were able to create a high-quality perovskite film on a flat surface, while still benefiting from the front-side texture.

“In this way, we succeeded in considerably improving the efficiency of a monolithic perovskite-silicon heterojunction tandem cell from 23.4 % to 25.5 %,” said the research coordinator Marko Jošt.

The German researchers have also conducted calculations on how different device designs with textures at various interfaces affect efficiency, by relying on a numerical model for complex 3D features and their interaction with light. “Based on these complex simulations and empirical data, we believe that an efficiency of 32.5 % can realistically be achieved – if we succeed to  incorporate high quality perovskites with a band gap of 1.66 eV,” Jošt continued.

Simulations realized at HZB laboratories also showed that the LM foil used on the front-side of the solar cell is particularly advantageous under diffuse light irradiation, and not only under perpendicularly incident light.