Correlating structure and electronic band-edge properties in organolead halide perovskites nanoparticles

Abstract

After having emerged as primary contenders in the race for highly efficient optoelectronics materials, organolead halide perovskites (OHLP) are now being investigated in the nanoscale regime as promising building blocks with unique properties. For example, unlike their bulk counterpart, quantum dots of OHLP are brightly luminescent, owing to large exciton binding energies that cannot be rationalized solely on the basis of quantum confinement. Here, we establish the direct correlation between the structure and the electronic band-edge properties of CH3NH3PbBr3 nanoparticles. Complementary structural and spectroscopic measurements probing long-range and local order reveal that lattice strain influences the nature of the valence band and modifies the subtle stereochemical activity of the Pb(2+) lone-pair. More generally, this work demonstrates that the stereochemical activity of the lone-pair at the metal site is a specific physicochemical parameter coupled to composition, size and strain, which can be employed to engineer novel functionalities in OHLP nanomaterials.

Localized holes and delocalized electrons in photoexcited inorganic perovskites: Watching each atomic actor by picosecond X-ray absorption spectroscopy

“…They are identical, and are also quite similar to the Pb L 3 spectrum reported 64 for CH 3 NH 3 PbBr 3 nanoparticles. They are overall rather featureless, which is typical of Pb L-edge spectra (Figure S10, supplementary material).…”

“…The Br K-edge spectra (Figure 1(a)) are somewhat different when recorded in total fluorescence yield (TFY) mode (see Sec. S.2), as can be seen in Figure S6 (supplementary material), but they resemble the spectrum reported for organic CH 3 NH 3 PbBr 3 perovskites 64 . Interestingly, the K-edge absorption spectrum of the Br − ions in the present samples is quite similar to that of the aqueous Br − , also recorded in PFY mode 65 .…”

Modulating Excitonic Recombination Effects through One‐Step Synthesis of Perovskite Nanoparticles for Light‐Emitting Diodes

“…This further restricts solution processing of subsequent device layers. Commonly used long‐chain organic capping/stabilizing ligands such as oleic acid and oleylamine can suppress charge injection, limit brightness, and result in high turn‐on voltage in LED devices . Thus, it is challenging to form a compact and ligand‐free film from preformed nanoparticles.…”

“…The average nanoparticle size is around 15 nm (inset of Figure a) with a lattice spacing of 0.29 nm corresponding to the (002) planes of MAPbBr 3 perovskite (Figure c). The selected‐area electron diffraction (SAED) pattern is made up of discrete spots as expected for nanocrystalline MAPbBr 3 perovskite (Figure d) . Optical absorption measurements showed an absorption onset for all films at 540 nm, corresponding to a band gap of approximately 2.30 eV, typical of MAPbBr 3 .The additional peak at 450 nm for the 20 % OABr film arises from the quasi 2 D perovskite (Figure e).…”

“…[23][24][25] This furtherr estricts solution processing of subsequent device layers.C ommonly used long-chain organic capping/stabilizingl igands such as oleic acid and oleylamine can suppress charge injection, limit brightness, and result in high turn-on voltage in LED devices. [29][30][31] Thus, it is challenging to form ac ompact and ligandfree film from preformed nanoparticles. Am ore elegant approach would be to induce the in situ/one-step formation of perovskite nanocrystals during the film formation process.…”