Vacuum-driven precrystallization enables efficient all-perovskite tandem solar cells

The power conversion efficiency of all-perovskite tandem solar cells (TSCs) suffers from inferior film quality and the susceptible fabrication processes of lead-tin narrow band-gap (Pb-Sn NBG) perovskite subcells. Herein, we developed a robust vacuum-driven precrystallization (VDP) strategy for high-quality Pb-Sn NBG perovskite films. Compared with traditional anti-solvent methods, the present precrystallization step could significantly retard the perovskite crystallization process by mild vacuum pumping. The above evolution process was quantitatively studied for the perovskite intermediate phase (PIP). The slow solvent extraction of the VDP strategy promotes a low surface energy of (100) plane-oriented precrystallization and provides sufficient time for grain ripening. The obtained Pb-Sn perovskite presented overall texture homogeneity and high crystallinity. The resulting all-perovskite TSCs yielded a top certified efficiency of 28.87% (28.09%) under reverse (forward) scan. Our VDP strategy promises efficient perovskite TSCs and contributes a key step toward robust and scalable photovoltaic technology.