Homogeneous crystallization of MA-free, wide-bandgap perovskite films via self-assembled monolayer capping for laminated silicon/perovskite tandem solar cells

Methylammonium (MA)-free wide-bandgap perovskite films with improved thermal/light stabilities have gained considerable attention for its application in silicon/perovskite tandem solar cells. However, compared to their MA counterparts, MA-free films often suffer from fast crystallization, resulting in uneven surface morphology, poor crystalline features, and excess PbI2 impurities. To modulate the crystallization dynamics of MA-free widebandgap Cs0.22FA0.78Pb(Br0.15I0.85)3 films, this study proposes a self-assembled monolayer (SAM)-capped crystallization strategy, wherein C42H52N6O4RuS2 (Z907) is added to the isopropanol antisolvent in the one-step solution process. The optimized Cs0.22FA0.78Pb(Br0.15I0.85)3 film has a wide bandgap of 1.68 eV with superior morphological/crystalline properties, enhanced thermal/moisture stability, and improved interfacial energylevel alignment. These favorable characteristics are attributed to the efficient coupling between the positive ion vacancies in the precursor, the -SCN and -COOH functional groups in Z907, and the superhydrophobic nonyl chains in the Z907 SAM. The semitransparent perovskite solar cells (PSCs) built with the optimized Cs0.22FA0.78Pb(Br0.15I0.85)3 films demonstrate substantially high power conversion efficiencies (PCEs) of 21.63 % @0.09 cm2 and 19.12 %@1 cm2. Furthermore, based on the high-efficiency PSCs, the corresponding twoterminal laminated silicon/perovskite tandem solar cells achieved record-high PCEs of 32.07 %@0.09 cm2 and 28.32 %@1 cm2 with negligible hysteresis and improved humidity/thermal stability.