Polymer macroligands passivate halide perovskite surfaces†

Abstract

Hybrid organic–inorganic hybrid perovskite (OIP) nanocrystals have gained considerable excitement due to high photoluminescence (PL) quantum yields, bandgap tunability, and narrow band emission, which are essential for photovoltaic devices, light emitting diodes (LEDs), and optical displays. While researchers have designed numerous ways to synthesize OIP nanomaterials, there is still a need to explore faster, cheaper, and scalable methods of making stable, highly performing nanomaterials for device applications. Polymers are commonly used to encapsulate OIP nanomaterials, yielding enhancements in long-term stability as well as improved PL properties. However, the exact impact of polymer chemical composition on perovskite nanocrystal growth and material properties is still unknown. Here, we reveal how polymer chemical composition directly modulates the formation of perovskite composite materials with ∼75 wt% perovskite with respect to polymer and the optical properties during a one-step, co-precipitation synthesis procedure. Specifically, a series of polymers were explored, poly(styrene) (PS), poly(4-vinylpyridine) (P4VP), poly(ethyleneimine) (PEI), poly(ethylene oxide) (PEO), poly(vinylpyrrolidone) (PVP), and poly(methyl methacrylate) (PMMA), to compare the structure and optical properties of the resulting OIP materials. Polymers with nitrogen-containing functional groups, such as amides, pyridine, and amines, are shown to preferentially bind to and passivate perovskite surfaces, acting as polymer macroligands. Nitrogen atoms in the polymer coordinate with under-coordinated lead ions on the perovskite surface, passivating surface defects and leading to an enhancement in the optical properties. Polymer macroligands also promote nanocrystal formation in a similar method as prototypical surface-active ligands used in nanocrystal syntheses. This work uncovers design rules for creating composite materials exhibiting desired nanostructures and enhanced optical properties for future OIP devices through the use of polymer macroligands.