Soft nanocomposites of lead bromide perovskite and polyurethane prepared via coordination chemistry for highly flexible, stable, and quaternary metal alloy-printed light emitting diodes

Abstract

The impressive luminescence properties, tunable bandgap, and cost-effective solution processing of methylammonium lead bromide (MAPbBr₃) make it a promising green-light emitter for next-generation displays. However, the commercialization of flexible light-emitting diodes (LEDs) based on MAPbBr₃ is hindered by the difficulties of (i) achieving precise morphological control and creating highly flexible pinhole-free MAPbBr₃ films, (ii) finding flexible cathode materials with low work functions suitable for effective electron injection at interfaces, and (iii) enhancing environmental and operational stability. To address these challenges, we herein designed solution-processed flexible perovskite LEDs incorporating polyurethane (PU) and an In–Ga–Zn–Sn liquid alloy (IGZS). The PU matrix rendered MAPbBr₃ films mechanically flexible and substantially reduced the amount of defects by coordinating Pb²⁺ ions through amide/carbonyl groups during crystallization. The use of printed IGZS cathodes, which had a lower work function (3.48 eV) than conventional solution-processed cathodes (>4 eV), reduced the energy gap at MAPbBr₃-electron injection layer-cathode interfaces and thus favored electron injection. The best-performing MAPbBr₃-PU device achieved a maximum luminance (2362.3 Cd m⁻²), current efficiency (8.79 Cd A⁻¹), and external quantum efficiency (1.93%) more than four times those of the pristine MAPbBr₃ device and exhibited high flexibility and durability, retaining over 87% of the above values after 1000 bending cycles at a radius of 7 mm. Moreover, the hydrophobic PU matrix effectively suppressed the infiltration of moisture and thus allowed for the excellent retention of normalized electroluminescence intensity (84.2% after 30 min) during the device operation.