Multifunctional Buffer Layer Engineering for Efficient and Stable Wide‐Bandgap Perovskite and Perovskite/Silicon Tandem Solar Cells

Abstract Inverted perovskite solar cells (PSCs) are preferred for tandem applications due to their superior compatibility with diverse bottom solar cells. However, the solution processing and low formation energy of perovskites inevitably lead to numerous defects at both the bulk and interfaces. We report a facile and effective strategy for precisely modulating the perovskite by incorporating AlO x deposited by atomic layer deposition (ALD) on the top interface. We find that Al 3+ can not only infiltrate the bulk phase and interact with halide ions to suppress ion migration and phase separation but also regulate the arrangement of energy levels and passivate defects on the perovskite surface and grain boundaries. Additionally, ALD‐AlO x exhibits an encapsulation effect through a dense interlayer. Consequently, the ALD‐AlO x treatment can significantly improve the power conversion efficiency (PCE) to 21.80 % for 1.66 electron volt (eV) PSCs. A monolithic perovskite‐silicon TSCs using AlO x ‐modified perovskite achieved a PCE of 28.5 % with excellent photothermal stability. More importantly, the resulting 1.55 eV PSC and module achieved a PCE of 25.08 % (0.04 cm 2 ) and 21.01 % (aperture area of 15.5 cm 2 ), respectively. Our study provides an effective way to efficient and stable wide‐band gap perovskite for perovskite‐silicon TSCs and paves the way for large‐area inverted PSCs.