Nonequilibrium Carrier Transport in Quantum Dot Heterostructures

Abstract

Understanding carrier dynamics and transport in quantum dot based heterostructures is crucial for unlocking their full potential for optoelectronic applications. Here we report the direct visualization of carrier propagation in PbS CQD solids and quantum-dot-in-perovskite heterostructures using femtosecond transient absorption microscopy. We reveal three distinct transport regimes: an initial superdiffusive transport persisting over hundreds of femtoseconds, an Auger-assisted subdiffusive transport before thermal equilibrium is achieved, and a final hopping regime. We demonstrate that the superdiffusive transport lengths correlate strongly with the degree of energetic disorder and carrier delocalization. By tailoring the perovskite content in heterostructures, we obtained a superdiffusive transport length exceeding 90 nm at room temperature and an equivalent diffusivity of up to 106 cm 2 s −1 , which is 4 orders of magnitude higher than the steady-state values. These findings introduce promising strategies to harness nonequilibrium transport phenomena for more efficient optoelectronic devices.

Passivating {100} Facets of PbS Colloidal Quantum Dots via Perovskite Bridges for Sensitive and Stable Infrared Photodiodes

“…A pump laser of 10 µW was used to minimize Auger recombination. [ 25 ] We used the biexponential function to fit decay trace and obtained two time constants. The shorter component (≈100 ps) is related to the process of exciton dissociation into free carriers.…”

“…[ 14–16 ] However, the wider‐bandgap perovskite matrix also inevitably impedes the carrier transport between the PbS CQDs, particularly when the matrix is thick. [ 25 ]…”

Assembly, Properties, and Application of Ordered Group II–VI and IV–VI Colloidal Semiconductor Nanoparticle Films

“…These microscopic measurements deliver both temporal and spatial information on exciton migration on sub-ns timescales and sub-micrometer lengthscales. [225,232,233] Exciton diffusion in a photoexcited PbS QD film can be divided in two The HOMO and LUMO of single QDs have a small contribution from {100} facets but no contributions from {110} and {111} facets, so there is a much stronger wave function overlap between QDs connected via {100} facets such as in a,b) a square configuration. In the c,d) hexagonal or e,f) rhombic configurations, the CBM wave functions only efficiently couple with second-nearest neighbors, reducing electron mobilities.…”

“…These microscopic measurements deliver both temporal and spatial information on exciton migration on sub‐ns timescales and sub‐micrometer lengthscales. [ 225,232,233 ] Exciton diffusion in a photoexcited PbS QD film can be divided in two different time regimes. [ 231 ] The “slow” (>500 fs) regime follows the trend expected from hopping, i.e., increasing diffusivity with decreasing interparticle distance, and diffusivities in the order of 1 cm 2 s −1 were recorded.…”

Efficient Hot Electron Transfer and Extended Separation of Charge Carriers at the 1P Hot State in Sb2Se3/CdSe p–n Heterojunction

“…On comparing the TA spectrum of Sb 2 Se 3 /CdSe with that of CdSe, we observed some interesting spectral differences. The TA spectra of CdSe show three distinct features: two photobleaching signals with maxima at 563 and 470 nm, attributed to band edge (1S) and hot state (1P) excitonic bleaches as discussed in the steady-state absorption spectra, and a positive absorption signal in the red region after 563 nm bleach ascribed to a stark induced biexciton effect. − The detailed experimental discussion is provided in the Supporting Information (Figure S9). To follow the charge carrier dynamics, carrier cooling, charge transfer, and recombination dynamics, we have carried out the temporal analysis of pure CdSe QDs, Sb 2 Se 3 QDs, as well as Sb 2 Se 3 /CdSe heterostructure systems at different wavelengths.…”