Carrier multiplication yields ofCdSeandCdTenanocrystals by transient photoluminescence spectroscopy

Abstract

Engineering semiconductors to enhance carrier multiplication (CM) could lead to increased photovoltaic cell performance and a significant widening of the materials range suitable for future solar technologies. Semiconductor nanocrystals (NCs) have been proposed as a favorable structure for CM enhancement, and recent measurements by transient absorption have shown evidence for highly efficient CM in lead chalcogenide and $\mathrm{CdSe}$ NCs. We report here an assessment of CM yields in $\mathrm{CdSe}$ and $\mathrm{CdTe}$ NCs by a quantitative analysis of biexciton and exciton signatures in transient photoluminescence decays. Although the technique is particularly sensitive due to enhanced biexciton radiative rates relative to the exciton, $k_{BX}^{\mathrm{rad}}>2k_X^{\mathrm{rad}}$, we find no evidence for CM in $\mathrm{CdSe}$ and $\mathrm{CdTe}$ NCs up to photon energies $\hslash \omega >3E_g$, well above previously reported relative energy thresholds.