Ergodic Light Propagation in a Half‐Cylinder Photonic Plate for Optimal Absorption in Perovskite Solar Cells

Abstract In an optical medium slab, a randomization of the interfaces will lead to an ergodic light propagation, implying a kind of light trapping that sets an upper limit for a broadband absorption enhancement factor. However, in thin film solar cells where such light trapping is most needed, it is not straightforward how the implementation of a surface randomization should be done. In addition, such randomization may also severely limit the electronic device performance. Here, a cylindrical periodic corrugation, which is named half‐cylinder photonic plate, is introduced at the light entering interface which leads to an ergodic light propagation. Advantage of such ergodicity is taken to enhance light absorption in a perovskite cell, physically separated by a planar glass substrate from such half‐cylinder photonic plate. Theoretically and experimentally it is demonstrated that the enhancement light absorption factor measured is close to the maximum possible for light trapping schemes using one interface periodic corrugations. This upper limit results from the ergodic light propagation that is achieved with a half‐cylinder photonic plate made from an optical transparent material with a low refractive index that minimizes light rejection by reflectivity.