  Hybrid lead halide perovskites with 2D stacking structures have recently
emerged as promising materials for optoelectronic applications. We report a
method for growing 2D nanosheets of hybrid lead halide perovskites (I, Br and
Cl), with tunable lateral sizes ranging from 0.05 to 8 microns, and a structure
consisting of n stacked monolayers separated by long alkylamines, tunable from
bulk down to n=1. The key to obtaining such a wide range of perovskite
properties hinged on utilizing the respective lead halide nanosheets as
precursors in a hot-injection synthesis that afforded careful control over all
process parameters. The layered, quantum confined (n small than 4) nanosheets
were comprised of major and minor fractions with differing n. Energy funneling
from low to high n (high to low energy) regions within a single sheet, mediated
by the length of the ligands between stacks, produced photoluminescent quantum
yields as high as 49 percent. These large, tunable 2D nanosheets could serve as
convenient platforms for future high efficiency optoelectronic devices.
