All-perovskite tandem solar cells (TSCs) promise high power conversion efficiency at a low cost1-4. Rapid efficiency improvement in small-area (<0.1 cm2) TSCs has been primarily driven by advances in low-bandgap (~1.25 eV) perovskite bottom subcells5-7. However, unsolved issues remain for wide-bandgap (WBG, >1.75 eV) perovskite top subcells8, which currently suffer from large voltage and fill factor (FF) losses, particularly for large-area (>1 cm2) TSCs. Here we develop a novel self-assembled monolayer (4-(7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (4PADCB) as a hole selective layer for WBG perovskite solar cells (PSCs), which facilitates subsequent growth of high-quality WBG perovskite over a large area with suppressed interfacial non-radiative recombination, enabling efficient hole extraction. Integrating 4PADCB in devices, we demonstrate a high open-circuit voltage (VOC) of 1.31 V in a 1.77-eV PSC, corresponding to a record low VOC-deficit of 0.46 V (with respect to the bandgap). With these WBG perovskite subcells, we report 27.0% (26.4% certified stabilized) monolithic all-perovskite TSCs with an aperture area of 1.044 cm2. The certified tandem cell shows an outstanding combination of a high VOC of 2.12 V and a FF of 82.6%. Our demonstration of the large-area TSCs with certified record efficiency is a key step toward upscaling all-perovskite tandem photovoltaic technology.
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