研究目的
To develop a method to extract a distinct carrier multiplication (CM) rate constant from experimental data of the relaxation time of hot charge carriers and the quantum yield (QY) of electron-hole pairs, and to apply this method to PbSe quantum dots.
研究成果
A method to determine the CM rate constant from experimental data of relaxation time and QY is presented and applied to PbSe quantum dots, yielding k_CM = (0.91 ± 0.05)ΔE^(1.5±0.2) ps?1. A simplified method provides an order-of-magnitude estimate of the CM rate constant just above the onset using only QY data. This approach is generally applicable for analyzing CM efficiency in various materials.
研究不足
The method is valid only for carrier excess energies up to twice the band gap, limiting it to single CM events. It neglects multiple CM events at higher energies, which can lead to inaccuracies. The electronic structure approximation and assumptions about energy division between electron and hole may not hold for all materials. The simplified method underestimates the CM rate constant compared to the full model.
1：Experimental Design and Method Selection:
The methodology involves deriving a model to extract an energy-dependent CM rate constant from experimental measurements of relaxation time and QY. It uses an electronic structure approximation with equidistant energy levels and assumes cooling governed by phonon emission. The model is fitted to experimental data using power law dependencies for rate constants.
2：Sample Selection and Data Sources:
Experimental data for relaxation time and QY are taken from previous works on 3.9 nm PbSe quantum dots with a band gap of 0.95 eV.
3：9 nm PbSe quantum dots with a band gap of 95 eV.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Not specified in the paper.
4：Experimental Procedures and Operational Workflow:
The method involves rescaling photoexcitation energy to electron excess energy, fitting equations to experimental data, and performing global fits to determine rate constants. A simplified method uses estimated energy loss rates when relaxation time data is unavailable.
5：Data Analysis Methods:
Fitting is done using custom code (provided in Supporting Information) to equations derived from the model, with parameters α and β for power law dependencies. Statistical techniques include global fitting to reduce uncertainties.
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