2D-3D heterostructure enables scalable coating of efficient low-bandgap Sn-Pb mixed perovskite solar cells

Low-bandgap photovoltaic absorbers based on mixed tin-lead (Sn-Pb) halide perovskites offer promising opportunities to fabricate efficient multi-junction solar cells. However, the current Sn-Pb mixed perovskite solar cells (PSCs) were mainly prepared using lab-scale spin-coating, greatly hindering their application for large-area device fabrication. Here, we report a simple and robust methodology for scalable deposition of dense and uniform Sn-Pb mixed perovskite films by one-step blade coating. High quality perovskite films with different Sn-Pb ratios are readily prepared by vacuuming the freshly coated precursor films followed by an anneal process. Solar cells based on these bladed Sn-Pb mixed perovskite absorbers showed decent photovoltaic behaviors. Further enhancement of device performance was realized via surface defects passivation using phenethy-lammonium bromide (PEABr). It was found that the formation of a thin layer of 2D Ruddlesden-Popper perovskite on top of 3D bulk perovskite significantly suppressed charge recombination. As a consequence, the open-circuit voltage (V-OC) of the solar cells (E-g = 1.35 eV) was dramatically lifted from 0.71 V to 0.78 V, yielding high efficiencies of over 15%. Moreover, notable improvement in shelf and moisture stability was observed due to the protection barrier of the 2D perovskite capping layer.