Quasi-Epitaxial Metal-Halide Perovskite Ligand Shells on PbS Nanocrystals
Sprache des Titels:
Epitaxial growth techniques enable nearly defect free heterostructures with coherent interfaces, which are of utmost importance for high performance electronic devices. While high vacuum technology based growth techniques are state-of-the art, here we pursue a purely solution processed approach to obtain nanocrystals with eptaxially coherent and quasi-lattice matched inorganic ligand shells. Octahedral metal-halide clusters, respectively 0-dimensional perovskites, were employed as ligands to match the coordination geometry of the PbS cubic rock-salt lattice. Different clusters, (CH3NH3+)(6-x)[M(x+)Hal6](6-x)- (Mx+=Pb(II), Bi(III), Mn(II), In(III), Hal=Cl, I), were attached to the nanocrystal surfaces via a scalable phase transfer procedure. The ligand attachment and coherence of the formed PbS/ligand core/shell interface was confirmed by combining the results from transmission electron microscopy, small angle x-ray scattering, nuclear magnetic resonance spectroscopy and powder x-ray diffraction. The lattice mismatch between ligand shell and nanocrystal core plays a key role in performance. In photoconducting devices the best performance (detectivity of 2x10^11 cm Hz 1/2/W with > 110 kHz bandwidth) was obtained with (CH3NH3)3BiI6 ligands, providing the smallest relative lattice mismatch of ~ -1%. PbS nanocrystals with such ligands exhibited in millimeter sized bulk samples in the form of pressed pellets a relatively high carrier mobility for nanocrystal solids of ~ 1.3 cm^2/Vs, a carrier lifetime of ~70 ?s, and a low residual carrier concentration of 2.6*10^13 cm^-3. Thus by selection of ligands with appropriate geometry and bond lengths optimized quasi-epitaxial ligand shells were formed on nanocrystals, which are beneficial for applications in optoelectronics.