Amino-acid-directed formation of quasi-zero-dimensional perovskites for high-purity blue and red luminescence

Spectral tuning in lead halide perovskite semiconductors is generally achieved by mixing halide compositions or by quantum confinement effects. However, mixed-halide perovskites exhibit undesirable phase separation during optical and electrical excitations, leading to spectral instability. Quantum confinement in pure-halide perovskite nanocrystals circumvents this problem, but requires synthetic protocols that involve high loading of long-chain insulating ligands. Here, we report a unique formation of quantum-confined perovskite through a one-step solution-casting process. This is achieved by the implementation of a short-chain 3-ammonium propionic acid (3-APA(+)) additive in the precursor solution, which directs quantum-confined nano-domains to assemble in situ during film formation. The bidentate amino and carboxylate functional groups of 3-APA(+), at an operational three-carbon spacing, coordinate effectively to adjacent halide and cesium surface atoms, and thus stabilizes the formation of quasi-zero dimensional nano-domains within an otherwise continuous thin film (i.e. embedded quantum dots within bulk film). This process allows precise spectral tuning in both pure-bromide and pure-iodide perovskite thin films to give high-purity blue and red luminescence, respectively. The resulting electroluminescent diodes exhibit remarkable spectral stability at 468 nm and 638 nm, which could find functional applications in trichromatic electronic color displays.