Optimizing Solid-State Ligand Exchange for Colloidal Quantum Dot Optoelectronics: How Much Is Enough?

Abstract

Progress in chalcogenide and perovskite CQD optoelectronics has relied to a significant extent on solid-state ligand exchanges (SSEs): the replacement of initial insulating ligands with shorter conducting linkers on CQD surfaces. Herein we develop a mechanistic model of SSE employing 3-mercapto­propionic acid (MPA) and 1,2-ethanedithiol (EDT) as the linkers. The model suggests that optimal linker concentrations lead to efficient exchange, resulting in ca. 200–300 exchanged ligands per CQD, a 50% thickness reduction of the initial film, decreased interdot spacing, a 15 nm red-shift in the excitonic absorption peak, and a 10× reduction in carrier lifetime. It is the combined effect of these physicochemical changes that has traditionally made 1% MPA and 10–2% EDT (v:v) the concentrations of choice for efficient CQD optoelectronics.

Recent Advances in Ligand Design and Engineering in Lead Halide Perovskite Nanocrystals

“…LHP NC Film Treatments: Solid-state ligand exchange is an alternative strategy to adjust the ligand shell composition of the LHP NCs in films. [412,414,415] This type of ligand exchange is especially promising for LHP NCs which, due to the labile nature of the native OA and OAm ligands, could be affected by solubility and stability issues in a traditional solution-phase ligand exchange strategy. [412] In a solid-state ligand exchange, the new ligand is dispersed in an antisolvent, which is then dropped onto the surface of a NC film (Figure 12H).…”

“…[412] In a solid-state ligand exchange, the new ligand is dispersed in an antisolvent, which is then dropped onto the surface of a NC film (Figure 12H). [412,414,415] However, due to the sensitivity of LHP NCs to nonpolar solvents, careful solvent choice is required to accomplish the ligand exchange process. [412] In one example of a solid-state ligand exchange performed on a LHP NC film, short chain ligands such as benzoic acid and 4-phenylbutylamine in a mixture of octane and benzene were used to replace native OA and OAm ligands (Figure 12H).…”

Low‐Threshold, Highly Stable Colloidal Quantum Dot Short‐Wave Infrared Laser enabled by Suppression of Trap‐Assisted Auger Recombination

“…For instance, in 5.6 nm QDs, the ASE spectra of PbS/ZnO blend samples having 15%, 20%, and 25% ZnO loading is correspondingly blue-shifted by ≈17, 24, 30 nm with respect to their bare-PbS counterpart (light-orange colored spectra in Figure 3c, A similar blue-shift is observed in the absorption spectra (See Figure S9 in the Supporting Information). We ascribe the blue-shifting of ASE and absorption spectra due to increasing inter-dot spacing of PbS-emitter CQDs, [28,29] Figure 3d provides a summary of the measured ASE in different sizes of PbS-emitter QDs as a function of ZnO content. As shown in Figure 3d, in all sizes of QDs, the ASE thresholds are clearly reduced by increasing the amount of ZnO loading in binary blend.…”

“…For instance, in 5.6 nm QDs, the ASE spectra of PbS/ZnO blend samples having 15%, 20% and 25% ZnO loading is correspondingly blue-shifted by ~17, 24, 30 nm with respect to their bare-PbS counterpart (light-orange coloured spectra in Figure 3c, A similar blue-shift is observed in the absorption spectra (See Supplementary Figure S9). We ascribe the blueshifting of ASE and absorption spectra due to increasing inter-dot spacing of PbS-emitter CQDs [28,29] , Figure 3d Finally, we combined the PbS/ZnO binary blend with 30% ZnO loading (our best performing ASE sample) with a second-order distributed feedback (DFB) resonator which provides strong in-plane feedback and lasing emission normal to the surface. Figure 4a illustrates the schematic of the DFB laser, where the film is pumped by a stripe excitation at normal incidence while the lasing emission is emitted from the surface of the device.…”

Colloidal Quantum Dot Photovoltaics Using Ultrathin, Solution-Processed Bilayer In2O3/ZnO Electron Transport Layers with Improved Stability

“…350 nm . Finally, 2-ethanedithiol (EDT) ligand capped PbS CQDs were used to form the HTL via a solid-state ligand-exchange-enabled layer-by-layer (LbL) process …”