Guilty as Charged: The Role of Undercoordinated Indium in Electron-Charged Indium Phosphide Quantum Dots

Abstract

Quantum dots (QDs) are known for their size-dependent optical properties, narrow emission bands, and high photoluminescence quantum yield (PLQY), which make them interesting candidates for optoelectronic applications. In particular, InP QDs are receiving a lot of attention since they are less toxic than other QD materials and are hence suitable for consumer applications. Most of these applications, such as LEDs, photovoltaics, and lasing, involve charging QDs with electrons and/or holes. However, charging of QDs is not easy nor innocent, and the effect of charging on the composition and properties of InP QDs is not yet well understood. This work provides theoretical insight into electron charging of the InP core and InP/ZnSe QDs. Density functional theory calculations are used to show that charging of InP-based QDs with electrons leads to the formation of trap states if the QD contains In atoms that are undercoordinated and thus have less than four bonds to neighboring atoms. InP coreonly QDs have such atoms at the surface, which are responsible for the formation of trap states upon charging with electrons. We show that InP/ZnSe core−shell models with all In atoms fully coordinated can be charged with electrons without the formation of trap states. These results show that undercoordinated In atoms should be avoided at all times for QDs to be stably charged with electrons.

Solvation Shifts the Band-Edge Position of Colloidal Quantum Dots by Nearly 1 eV

“…Our computational model is composed of a PbS cQD with Pb 140 S 85 Cl 110 stoichiometry corresponding to a diameter of 3.4 nm, and one layer of explicit solvent molecules (Figure A). This nonstochiometric model was used to resemble the experimental composition of PbS cQDs, with excess of Pb atoms passivated by Cl ligands required to keep charge balance and used for computational simplicity, and is the same as the model used in ref , with chloride ligands instead of the iodide ligands used in that work.…”

Surface Passivation toward Multiple Inherent Dangling Bonds in Indium Phosphide Quantum Dots

“…17 However, little attention has been paid to the surface In−DBs and remains inadequately explored. 18 Previous theoretical calculations also reveal that the surface undercoordinated In atoms of InP QDs can lead to the formation of trap states when additional electrons are introduced. 18 Here, we present a facile one-step surface peeling and passivation treatment toward both In and P−DBs for aminophosphide source-based InP QDs via introducing inorganic pseudohalogen ammonium salt.…”

“…18 Previous theoretical calculations also reveal that the surface undercoordinated In atoms of InP QDs can lead to the formation of trap states when additional electrons are introduced. 18 Here, we present a facile one-step surface peeling and passivation treatment toward both In and P−DBs for aminophosphide source-based InP QDs via introducing inorganic pseudohalogen ammonium salt. First, focusing on the In−DBs, the ammonium cations from the ammonium hexafluorophosphate (NH 4 PF 6 ) decomposition can eliminate the surface In−DBs by forming P−NH 4 bonds.…”

“…Considering the corrosivity and exposure hazards of HF, several moderate alternative etchants, such as NH 4 F, NH 4 HF 2 , and ionic liquid 1-hexyl-3-methyl-imidazolium tetrafluoroborate (hmim BF 4 ), have been also examined efficiently as etching agents to eliminate the surface phosphorus vacancies. ,− Fluoride ions have been proved to improve the PLQYs by either filling phosphorus vacancy sites on the surface of InP QDs or etching away the P–DBs and PO x oxidation layer . However, little attention has been paid to the surface In–DBs and remains inadequately explored . Previous theoretical calculations also reveal that the surface undercoordinated In atoms of InP QDs can lead to the formation of trap states when additional electrons are introduced …”

“…However, little attention has been paid to the surface In–DBs and remains inadequately explored . Previous theoretical calculations also reveal that the surface undercoordinated In atoms of InP QDs can lead to the formation of trap states when additional electrons are introduced …”