| We have measured the temperature-dependent photoluminescence (PL) and quantum yield (QY) of a series of alkanedithiol-treated PbS quantum dot (QD) films as a function of QD size and the length of the alkane chain. These films have PLQYs ranging 2% - 40% at 20 K, with the lowest values measured for shorter ligands and larger QD sizes. All films show PL quenching and shifting/narrowing with increased temperature characterized by exponential (Urbach) band tail behavior. The PLQY vs temperature takes a form derived from an Arrhenius-like dependence of activated charge separation. We also find temperature-dependent photoconductivity (sigma), showing an Arrhenius relationship with inverse temperature (T-0.5 at lower temperature matching variable-range hopping model and T-1 at higher temperature corresponding to near-neighbor hopping model), is inversely related with temperature-dependent PL. This indicates that temperature-dependent PL is a relevant measure of transport properties in the presence of deep trap states and reasonably high charge carrier mobilities. |
