High Activity Phosphine-Free Selenium Precursor Solution for Semiconductor Nanocrystal Growth

A phosphine-free selenium nanocrystal precursor solution has been synthesized by heating elemental selenium powder in 1-octadecene (ODE). This mixture was characterized by UV−vis absorption, photoluminescence excitation (PLE), nuclear magnetic resonance (NMR), Se X-ray absorption spectroscopy (Se-XAS), electron impact mass spectrometry (EIMS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES) to establish identifiable spectroscopic and chemical signatures that can be correlated to the chemical efficacy of the precursor for the growth of metal selenide nanocrystals. Highly temperature dependent rates of selenium dissolution and deactivation of the resultant precursor are demonstrated and optimal preparation times for the most reactive precursor are determined. Distinctive features in the PLE spectrum provide a rapid estimate of the reactivity of the as-prepared Se-ODE precursor. NMR and XAS data strongly indicate both Se−Se and Se−C bonding are present in the precursor solution, suggesting that simple selenium dissolution. This is also confirmed by (EI) mass spectra where (ODE+2Se) and (2ODE+2Se) were only found in the most active Se-ODE solutions. Se-ODE is not only chemically more benign than the traditionally employed trioctylphosphine selenide (TOPSe), but it is also demonstrated that optimized Se-ODE has nearly twice the reactivity of TOPSe for Se deposition onto CdSe core particles at 220 °C.