Manipulating Wide-Band-Gap Perovskite Compositions via Br Sources for Highly Efficient Perovskite/Silicon Tandem Solar Cells

The integration of perovskites with silicon for constructing tandem solar cells (TSCs) signifies a promising route in photovoltaic technology. To optimize the compatibility with silicon bottom cells, the perovskite absorbing layer necessitates an appropriate band gap of 1.68 eV. However, fabricating a wide-band-gap perovskite layer with conformal deposition on textured silicon bottom cells presents a significant challenge. Here, we investigate three different common bromide sources (formamidinium bromide (FABr), methylammonium bromide (MABr), and lead bromide (PbBr 2 )) to manipulate the band gaps of the resultant perovskite films, as fabricated by the vapor–solution hybrid method. Results show that incorporation of FABr facilitates the crystallization of wide-band-gap perovskite films with larger grain sizes and reduced PbI 2 residues in comparison with MABr- and PbBr 2 -based counterparts. The perovskite film fabricated with the FABr source also exhibits the best energy-level alignment and the lowest defect density among the three precursor types, thus promoting an effective carrier transport and extraction at the device interfaces. As a result, the top power conversion efficiency of the target perovskite/silicon TSCs reaches 28.69% with an open-circuit voltage of 1.85 V and a fill factor of 79.13%. Our work reveals the fundamental differences in applying different Br – sources and offers a practical guideline for achieving highly efficient perovskite/silicon TSCs.