Homogenizing Buried Interfacial Contact and Halide Distribution in Wide-Bandgap Perovskites for Efficient Tandem Solar Cells

Top-cell candidates for tandem photovoltaic devices are promisingly represented by wide-bandgap perovskite solar cells. Nonetheless, their efficacy has been subject to considerable constraints arising from phase separation issues, which are induced by inhomogeneous interfacial contact and uneven halide distribution, which in turn leads to intense nonradiative recombination and ultimately degrades device performance. In this work, a benzylammonium thiocyanate (BnASCN) interlayer is introduced at the buried interface of wide-bandgap perovskites to synergistically homogenize both the buried interfacial contact and the halide distribution. The results demonstrate that BnASCN can effectively suppress the aggregation of aluminum oxide (Al 2 O 3 ) nanoparticles, thus constructing a uniform buried interface; meanwhile, this material can form strong coordination interactions with halide ions in the perovskite, realizing a homogeneous halide distribution. These optimizations enhance the crystallinity of wide-bandgap perovskite films. The as-fabricated wide-bandgap device (1.68 eV) exhibits a maximum power conversion efficiency (PCE) of 22.5%. Furthermore, the stability of the wide-bandgap devices is significantly improved. Under continuous one-sun illumination in air, the BnASCN-modified single-junction device maintains 90% of its original PCE after 150 h of maximum power point tracking (MPPT), far exceeding the 50% retained by the control device. When integrated into perovskite/silicon tandem cells, the optimized devices achieve a superior PCE of 30.9%.