Buried Interface Modulation Using Self‐Assembled Monolayer and Ionic Liquid Hybrids for High‐Performance Perovskite and Perovskite/CuInGaSe2 Tandem Photovoltaics

Effective modifications for the buried interface between self-assembled monolayers (SAMs) and perovskites are vital for the development of efficient, stable inverted perovskite solar cells (PSCs) and their tandem photovoltaics. Herein, an ionic-liquid-SAM hybrid strategy is developed to synergistically optimize the uniformity of SAMs and the crystallization of perovskites above. Specifically, an ionic liquid of 1-butyl-3-methyl-1H-imidazol-3-iumbis((trifluoromethyl)sulfonyl)amide (BMIMTFSI) is incorporated into the SAM solution, enabling reduced surface roughness, improved wettability, and a more evenly distributed surface potential of the SAM film. Leveraging this optimized substrate, a favorable growth of high-quality perovskite crystals is achieved. Furthermore, the introduced functional ions readily bond with the perovskites, effectively passivating undesirable cation or halide vacancies of the perovskite near the buried interface. Remarkably, high power conversion efficiencies (PCEs) of 25.68% and 22.53% are obtained for normal-bandgap (≈1.55 eV) and wide-bandgap (WBG) (≈1.66 eV) PSCs along with improved operational stability. Additionally, a champion PCE of 19.50% is achieved for semitransparent WBG PSCs, further delivering an impressive PCE of 28.34% for integrated four-terminal tandem photovoltaics when combined with CuInGaSe₂ solar cells.