Perovskite Deposition on Textured Silicon: Conformal Coating over Pyramids

… more less Perovskite deposition on textured silicon is a hard step in making a tandem. Factory silicon wafers have tiny pyramids on the front, a few microns high. They bounce light back into the cell so less is lost. But a spin-coated perovskite ink does not follow those pyramids. The liquid pools in the valleys and leaves the peaks bare or very thin. Where the film is missing, the top and bottom contacts touch. That makes a shunt, a short path that leaks current, and you see a low fill factor and low voltage on the J-V curve. There are three main fixes. One is to polish the front flat. Coating is then easy, but you lose the light trapping and must add other anti-reflection steps. A second is to use smaller pyramids and a thicker ink that can cover them. A third is a hybrid two-step route. First, the lead halide is laid down by evaporation, which coats every face evenly. Then an organic salt solution is applied and turns it into perovskite. Each route trades ease of making against light lost. When you read a tandem result, check the wafer front: polished, small texture, or full texture. After this Concept you can explain why spin coating fails on textured silicon and pick a coating route for a given wafer.