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

Abstract

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) counterparts2,3. 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 itself4,5. 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 (Voc) 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. Using a mixture of 4-fluorophenethylamine and 4-trifluoromethyl-phenylammonium to create a tailored 2D perovskite layer reduces the inhomogeneity at the top interface of all-perovskite tandem cells and results in the highest efficiency reported so far.