Tuning Crystallization for Highly Efficient Perovskite Silicon Tandem Solar Cells

Perovskite solar cells have the advantages of a strong absorption edge, defect tolerance, and potential cheap production due to easy production methods such as spin coating or slot-die coating as a highly scalable production method. In the industry, double-sided textured (micro-meter sized pyramid) silicon is commonly produced to decrease reflection losses and improve light trapping. Solution-based processing methods of perovskite on top of the textured Si showed low conformality, which resulted in shunts and non-working solar cells. To overcome this issue, the hybrid route was developed, in which inorganic precursors are co-evaporated using the thermal vapor deposition technique and then organic precursors are spin-coated followed by a thermal annealing. By doing that, high conformality of perovskite thin films on top of the textured silicon is achieved. However, the resulting perovskite grain size is rather low, which can lower the bulk quality. In this work, various additives were used to increase the grain size, and their working mechanisms were studied. In addition, we study the consequences of different grain sizes at the tandem level with respect to device efficiency as well as stability. Moreover, using the thermodynamics fundamentals of crystallization, we hypothesize for the first time a common general explanation for the working mechanism of all the different additives used.