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To achieve high power conversion efficiency in perovskite/silicon tandem solar cells, it is necessary to develop a promising wide-bandgap perovskite absorber and processing techniques in relevance. To date, the performance of devices based on wide-bandgap perovskite is still limited mainly by carrier recombination at their electron extraction interface. Here, we demonstrate assembling a binary two-dimensional perovskite by both alternating-cation-interlayer phase and Ruddlesden−Popper phase to passivate perovskite/C60 interface. The binary two-dimensional strategy takes effects not only at the interface but also in the bulk, which enables efficient charge transport in a wide-bandgap perovskite solar cell with a stabilized efficiency of 20.79% (1 cm2). Based on this absorber, a monolithic perovskite/silicon tandem solar cell is fabricated with a steady-state efficiency of 30.65% assessed by a third party. Moreover, the tandem devices retain 96% of their initial efficiency after 527 h of operation under full spectral continuous illumination, and 98% after 1000 h of damp-heat testing (85 °C with 85% relative humidity). The performance of wide bandgap perovskite solar cells is limited by the carrier recombination at their electron extraction interface. Here, the authors assemble binary 2D perovskites for efficient charge transport and realizing stable perovskite/silicon tandems with device efficiency over 30%. [ABSTRACT FROM AUTHOR]

Spontaneous polarization plays a crucial role in manifesting unprecedented properties in polar materials, yet its mechanism remains relatively unexplored. We lack certainty regarding how asymmetric groups distort to generate spontaneous polarization, and the understanding of how spontaneous polarization changes with temperature is incomplete. In this study, we have grown a high-quality crystal of metal borate halides, specifically Mn3B7O13Cl, as a proof of principle for spontaneous polarization in polar materials. Our results for Mn3B7O13Cl indicate that approximately 80% of spontaneous polarization originates from [MnCl2O4], and the magnitude of spontaneous polarization associated with [MnCl2O4] remains nearly constant with temperature. Meanwhile, the temperature-dependent variation in spontaneous polarization is entirely governed by the [BO4–BO3] groups. These findings provide insight into the mechanism of spontaneous polarization in polar materials, particularly metal borate halides, and offer a new pathway for inducing properties related to spontaneous polarization in this class of materials. [ABSTRACT FROM AUTHOR]