Color Patterning of Luminescent Perovskites via Light-Mediated Halide Exchange with Haloalkanes.

Lead halide perovskite possesses a semiconductor bandgap that is readily tunable by a variation in its halide composition. Here, a photo-activated halide exchange process between perovskite nanocrystals and molecular haloalkanes is reported, which enables the perovskite luminescence to be controllably shifted across the entire visible spectrum. Mechanistic investigations reveal a mutual exchange of halogens between the perovskite crystal surface and a chemisorbed haloalkane, yielding nanocrystals and haloalkanes with mixed halide contents. Exchange kinetics studies involving primary, secondary, and tertiary haloalkanes show that the rate of reaction is governed by the activation barrier in the breakage of the covalent carbon-halogen (CX) bond, which is a function of the CX bond energy and carbon radical stability. Employing this halide exchange approach, a micrometer-scale trichromatic patterning of perovskites is demonstrated using a light-source-integrated inkjet printer and tertiary haloalkanes as color-conversion inks. The haloalkanes volatilize after halide exchange and leave no residues, thereby offering significant processing advantage over conventional salt-based exchange techniques. Beyond the possible applications in new-generation micro-LED and electroluminescent quantum dot displays, this work exemplifies the rich surface and photochemistry of perovskite nanocrystals, and could lead to further opportunities in perovskite-based photocatalysis and photochemical sensing.