Size and composition dependent multiple exciton generation efficiency in PbS, PbSe, and PbS(x)Se(1-x) alloyed quantum dots.

Using ultrafast transient absorption and time-resolved photoluminescence spectroscopies, we studied multiple exciton generation (MEG) in quantum dots (QDs) consisting of either PbSe, PbS, or a PbSxSe1-x alloy for various QD diameters with corresponding bandgaps (Eg) ranging from 0.6 to 1 eV. For each QD sample, we determine the MEG efficiency, ηMEG, defined in terms of the electron-hole pair creation energy (εeh) such that ηMEG = Eg/εeh.

Comparison of carrier multiplication yields in PbS and PbSe nanocrystals: the role of competing energy-loss processes.

Infrared band gap semiconductor nanocrystals are promising materials for exploring generation III photovoltaic concepts that rely on carrier multiplication or multiple exciton generation, the process in which a single high-energy photon generates more than one electron-hole pair. In this work, we present measurements of carrier multiplication yields and biexciton lifetimes for a large selection of PbS nanocrystals and compare these results to the well-studied PbSe nanocrystals. The similar bulk properties of PbS and PbSe make this an important comparison for discerning the pertinent properties that determine efficient carrier multiplication.

Anomalous independence of multiple exciton generation on different group IV-VI quantum dot architectures.

Multiple exciton generation (MEG) in PbSe quantum dots (QDs), PbSe(x)S(1-x) alloy QDs, PbSe/PbS core/shell QDs, and PbSe/PbSe(y)S(1-y) core/alloy-shell QDs was studied with time-resolved optical pump and probe spectroscopy. The optical absorption exhibits a red-shift upon the introduction of a shell around a PbSe core, which increases with the thickness of the shell. According to electronic structure calculations this can be attributed to charge delocalization into the shell.

Comparing multiple exciton generation in quantum dots to impact ionization in bulk semiconductors: implications for enhancement of solar energy conversion.

Multiple exciton generation (MEG) in quantum dots (QDs) and impact ionization (II) in bulk semiconductors are processes that describe producing more than one electron-hole pair per absorbed photon. We derive expressions for the proper way to compare MEG in QDs with II in bulk semiconductors and argue that there are important differences in the photophysics between bulk semiconductors and QDs. Our analysis demonstrates that the fundamental unit of energy required to produce each electron-hole pair in a given QD is the band gap energy.

Characterization of the unimolecular water elimination reaction from 1-propanol, 3,3,3-propan-1-ol-d3, 3,3,3-trifluoropropan-1-ol, and 3-chloropropan-1-ol.

The unimolecular reactions of 1-propanol, 3,3,3-propan-1-ol-d3, 3,3,3-trifluoropropan-1-ol, and 3-chloropropan-1-ol have been studied by the chemical activation technique. The recombination of CH3, CD3, CF3, and CH2Cl radicals with CH2CH2OH radicals at room temperature was used to generate vibrationally excited CH3CH2CH2OH, CD3CH2CH2OH, CF3CH2CH2OH, and CH2ClCH2CH2OH molecules. The principal unimolecular reaction for propanol and propanol-d3 with 90 kcal mol(-1) of vibrational energy is 1,2-H2O elimination with rate constants of 3.

Variations in the quantum efficiency of multiple exciton generation for a series of chemically treated PbSe nanocrystal films.

We study multiple exciton generation (MEG) in two series of chemically treated PbSe nanocrystal (NC) films. We find that the average number of excitons produced per absorbed photon varies between 1.0 and 2.