Rough versus planar interfaces: How to maximize the short circuit current of perovskite single and tandem solar cells

Abstract

The short circuit current of perovskite/silicon tandem solar cells has to be increased to realize solar cells with energy conversion efficiencies exceeding the records of single junction solar cells. Photon management allows for increasing the short-circuit current and energy conversion efficiency of perovskite single junction and perovskite/silicon tandem solar cells due to improved light incoupling and/or light trapping. In this study, an electrically flat but optically rough solar cell design is investigated, which combines the benefit of reaching high short-circuit currents, while maintaining the integrity of perovskite films processed on planar substrates or surfaces. Consequently, the perovskite films exhibit electrical properties comparable to planar perovskite solar cells, which allows for achieving solar cells with high open circuit voltage and fill factors. Electrically flat but optically rough perovskite solar cell structures can be successfully implemented because the perovskite material system and the contact materials of the solar cells exhibit comparable refractive indices. This sets the perovskite material system with its low refractive index apart from other high refractive index materials like silicon or germanium. Hence the proposed design of an electrically flat but optically rough solar cell cannot be applied to silicon or germanium solar cells. The design of perovskite single junction solar cells is discussed, and electrically flat but optically rough solar cells are compared to electrically and optically rough solar cells. The design of perovskite/silicon tandem solar cells is investigated by using a hybrid approach, which combines Finite Difference Time Domain optical simulations of perovskite top and experimentally measured crystalline bottom solar cells. Detailed guidelines are provided on how to achieve high short-circuit currents.