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 (PbBr2)) 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 PbI2 residues in comparison with MABr- and PbBr2-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.