Electronic and surface properties of PbS nanoparticles exhibiting efficient multiple exciton generationElectronic supplementary information (ESI) available: Comparison of transients recorded with stirring rates of 0, 500 and 1000 rpm, valence band spectra of 'aged' and 'fresh' PbS nanoparticles, absorption spectra of olive-oil-capped PbS nanoparticles. See DOI: 10.1039/c1cp22330e

Ultrafast transient absorption measurements have been used to study multiple exciton generation in solutions of PbS nanoparticles vigorously stirred to avoid the effects of photocharging. The threshold and slope efficiency of multiple exciton generation are found to be 2.5 ± 0.2 × E g and 0.34 ± 0.08, respectively. Photoemission measurements as a function of nanoparticle size and ageing show that the position of the valence band maximum is pinned by surface effects, and that a thick layer of surface oxide is rapidly formed at the nanoparticle surfaces on exposure to air. Ultrafast transient absorption and photoemission measurements have been used to study multiple exciton generation and measure the electronic and surface properties of PbS nanoparticles.