Researchers at Helmholtz-Zentrum Berlin (HZB) have demonstrated 25.5% efficiency for monolithic perovskite/silicon tandem solar cells using textured foil. In addition, the impact of texture position on performance and energy yield is simulated in their new work.
Tandem solar cell device schematics of the experimentally realized architecture and SEM cross section image of the top cell
The research team used a textured light management (LM) foil on the front-side of a tandem solar cell processed on a wafer with planar front-side and textured back-side. Consequently, the PCE of monolithic, 2-terminal perovskite/silicon-heterojunction tandem solar cells was improved from 23.4% to 25.5%. This approach replaced the use of textured silicon wafers, that can be utilized for light management but are typically not compatible with perovskite solution processing.
In addition, the team validated an advanced numerical model for their fabricated device and used it to optically optimize a number of device designs with textures at different interface with respect to the PCE and energy yield. These simulations predict a slightly lower optimal bandgap of the perovskite top cell in a textured device as compared to a flat one and demonstrate strong interdependency between the bandgap and the texture position in the monolithic stack.
The researchers estimate the PCE potential for the best performing both-side textured device to be 32.5% for a perovskite bandgap of 1.66 eV. Furthermore, the results show that under perpendicular illumination conditions, for optimized designs, the LM foil on top of the cell performs only slightly better than a flat antireflective coating. However, under diffuse illumination, the benefits of the LM foil are much greater.
Finally, the researchers calculated the energy yield for the different device designs, based on true weather data for three different locations throughout the year, taking direct as well as diffuse illumination fully into account. The results further confirm the benefits of front-side texture, even more for BIPV applications.
Overall, the team reported that devices built on a both-side textured silicon wafer perform best. However, it was shown int their work that devices with textured LM foils on the cell's front-side are a highly efficient experimental alternative.
