Passivation of Electron Trap States in InP Quantum Dots with Benzoic Acid Ligands

Abstract

Low toxicity indium phosphide (InP) quantum dots represent an attractive alternative to heavy-metal-based quantum dots (QDs) in numerous applications including lighting, displays, and photosensitization. However, low photoluminescence quantum yields (PLQYs) resulting from a high density of surface trap states ultimately limit the applications of as-synthesized InP QDs in commercial products. Postsynthetic treatment with Z-type ligands (two-electron acceptors) is often used to passivate the surface traps of the InP QDs, while approaches using X-type ligands (oneelectron donors) are less prevalent due to the lack of understanding of how the X-type ligands function to passivate the surface traps. In this study, we report a postsynthetic surface passivation utilizing benzoic acid (BZA) as an X-type surface ligand. To understand how BZA impacts their electronic structure, we conducted spectroscopic studies on InP QDs with various surface modifications, including in situ fluorination and postsynthetic BZA treatment. A comparison of a variety of time-resolved spectroscopic techniques reveals that BZA can selectively remove electron trap states in InP QDs by passivating unsaturated indium atoms at the QD surface. When the BZA treatment is used in combination with a well-established fluoride treatment, the PLQYs of these unshelled InP QDs exceeds 20%. This research advances our understanding of the function of X-type ligands at the InP QD surface and their role in the passivation of unsaturated indium atoms to reduce electron trap states.

Engineering Long-Lived Blue Photoluminescence from InP Quantum Dots Using Isomers of Naphthoic Acid

“…All these absorption features symmetrically recover during the 6 ns time window of this experiment and this difference spectrum persists into the 100 ns timescale as observed using conventional laser flash photolysis, consistent with the average lifetimes determined by TRPL. 33,36 In the surface-anchored 1and 2-NA InP QD samples, significantly accelerated recovery of the InP GSB was observed, occurring within 2 ns in both instances, concomitant with the growth of the characteristic 1and 2-NA T 1 → T n absorptions near 430 nm, overlapping with the InP-based isosbestic point at 438 nm (Figure 3b,c). 37,38 As a result, the molecular triplet formation kinetics were monitored at 438 nm and fitted using a stretched exponential function as described in the Supporting Information.…”

“…In these materials, the transient PL spectrum measured at 77 K yielded quantitatively similar results to the pristine InP sample, namely, a peak centered at 549 nm measured at a 10 μs time delay, as shown in Figure 4a. Because BZA is known to selectively passivate the surface electron trap states in InP QDs, 33 the broad peak at 549 nm universally measured in all samples shown in Figure 4a is therefore assigned to the hole trap state PL in these materials. 33,39 Figure 4b presents the normalized transient PL spectra recorded for the InP/1-NA QDs at a 500 ns delay time, compared to the spectrum measured at 100 ns along with the static 77 K PL spectrum of molecular 1-NA in toluene.…”

“…Because BZA is known to selectively passivate the surface electron trap states in InP QDs, 33 the broad peak at 549 nm universally measured in all samples shown in Figure 4a is therefore assigned to the hole trap state PL in these materials. 33,39 Figure 4b presents the normalized transient PL spectra recorded for the InP/1-NA QDs at a 500 ns delay time, compared to the spectrum measured at 100 ns along with the static 77 K PL spectrum of molecular 1-NA in toluene. Two unique emission features are revealed in the 500 ns spectrum having peaks at 503 nm and 584 nm, which coincide with the peaks of the 77 K phosphorescence spectrum of the 1-NA chromophore.…”

Synergistic Effect of Halogen Ions and Shelling Temperature on Anion Exchange Induced Interfacial Restructuring for Highly Efficient Blue Emissive InP/ZnS Quantum Dots

“…[15][16][17][18] To date, considerable research has focused on growth kinetics and synthetic strategies of InP QDs. [19][20][21][22][23][24][25] Apart from the common method where indium acetate and tris(trimethylsilyl)phosphine ((TMS) 3 P) are utilized, indium halide is widely employed in the preparation of InP/ ZnS QDs combining with zinc halide and amino phosphine recently owing to its low cost and safety. As has been reported, halide plays a critical role in its nucleation and surface chemistry.…”

Aminophosphine-derived, high-quality red-emissive InP quantum dots by the use of an unconventional in halide

“…In an effort to examine the possible origin affecting PL QY, X-ray photoelectron spectroscopic (XPS) analysis was carried out on InBr 3 - and InCl 3 -based red emissive InP cores. The presence of chloride adsorbed on the core surface, possibly serving as an X-type ligand on the undercoordinated surface In atom as an electron trap site, 24–26 is evident from both samples, as shown in high-resolution scans of Cl 2p photoelectron peaks (Fig. 3a).…”