Improving interface quality for 1-cm 2 all-perovskite tandem solar cells

All-perovskite tandem solar cells provide high power conversion efficiency at a low cost 1 – 4 . Rapid efficiency improvement in small-area (<0.1 cm 2 ) tandem solar cells has been primarily driven by advances in low-bandgap (approximately 1.25 eV) perovskite bottom subcells 5 – 7 . However, unsolved issues remain for wide-bandgap (> 1.75 eV) perovskite top subcells 8 , which at present have large voltage and fill factor losses, particularly for large-area (>1 cm 2 ) tandem solar cells. Here we develop a self-assembled monolayer of (4-(7 H -dibenzo[ c,g ]carbazol-7-yl)butyl)phosphonic acid as a hole-selective layer for wide-bandgap perovskite solar cells, which facilitates subsequent growth of high-quality wide-bandgap perovskite over a large area with suppressed interfacial non-radiative recombination, enabling efficient hole extraction. By integrating (4-(7 H -dibenzo[ c,g ]carbazol-7-yl)butyl)phosphonic acid in devices, we demonstrate a high open-circuit voltage ( V OC ) of 1.31 V in a 1.77-eV perovskite solar cell, corresponding to a very low V OC deficit of 0.46 V (with respect to the bandgap). With these wide-bandgap perovskite subcells, we report 27.0% (26.4% certified stabilized) monolithic all-perovskite tandem solar cells with an aperture area of 1.044 cm 2 . The certified tandem cell shows an outstanding combination of a high V OC of 2.12 V and a fill factor of 82.6%. Our demonstration of the large-area tandem solar cells with high certified efficiency is a key step towards scaling up all-perovskite tandem photovoltaic technology.