Homogenized contact in all-perovskite tandems using tailored 2D perovskite

The fabrication of scalable all-perovskite tandem solar cells is considered an attractive route to commercialize perovskite photovoltaic modules¹. However, the certified efficiency of 1-cm²-scale all-perovskite tandem solar cells lags behind their small-area (approximately 0.05-cm²) counterparts^2,3. This performance deficit originates from inhomogeneity in wide-bandgap (WBG) perovskite solar cells (PSCs) at a large scale. The inhomogeneity is known to be introduced at the bottom interface and within the perovskite bulk itself^4,5. Here we uncover another crucial source for the inhomogeneity-the top interface formed during the deposition of the electron transport layer (ETL; C₆₀). Meanwhile, the poor ETL interface is also a notable limitation of device performance. We address this issue by introducing a mixture of 4-fluorophenethylamine (F-PEA) and 4-trifluoromethyl-phenylammonium (CF3-PA) to create a tailored 2D perovskite layer (TTDL), in which F-PEA forms a 2D perovskite at the surface, reducing contact losses and inhomogeneity, and CF3-PA enhances charge extraction and transport. As a result, we demonstrate a high open-circuit voltage (V_oc) of 1.35 V and an efficiency of 20.5% in 1.77-eV WBG PSCs at a square-centimetre scale. By stacking with a narrow-bandgap (NBG) perovskite subcell, we report 1.05-cm² all-perovskite tandem cells delivering 28.5% (certified 28.2%) efficiency, the highest reported so far. Our work showcases the importance of treating the top perovskite/ETL contact for upscaling PSCs.