Non-contact laser polishing and reconstruction towards high-efficiency all-perovskite tandem solar cells

The performance of all-perovskite tandem solar cells is critically hindered by the defective and high-roughness surfaces of lead-tin narrow-bandgap subcells, which induce non-radiative recombination and impede carrier extraction. Herein, we report a robust and multifunctional strategy to convert the above narrow-bandgap perovskite surface into an efficient and smooth one by a picosecond ultraviolet pulsed laser polishing technology combined with surface reconstruction. The polished surface is decoded as [PbI₆]⁴⁻/[SnI₆]⁴⁻ octahedral frameworks with metastable A-site vacancies. By screening guanidinium bromide as an A-site passivator, the polished surface is reconstructed into a guanidinium-cesium-based perovskite phase, substantially enhancing carrier extraction and suppressing ion migration. The resulting single-junction lead-tin and tandem solar cells, fabricated via an antisolvent-free method, achieve efficiencies of 23.47% (certified) and 29.80%, respectively, alongside exceptional operational stability. This versatile interface engineering paradigm surmounts a pivotal barrier in the advancement of next-generation photovoltaic technologies.