Decoupling Electron and Hole Injection Dynamics in Colloidal Nanocrystals via Potentiostatic Polarization Spectroelectrochemistry.

The outstanding optoelectronic potential of colloidal nanocrystals has driven intensive study of their charge carrier behavior. However, conventional spectroelectrochemistry (SEC) may yield results that deviate from practical device operation because it typically relies on gradual potential scans. Here, we investigate mixed-phase and pure wurtzite CdSe/CdS core/shell nanocrystals using potentiostatic polarization SEC. Mixed-phase nanocrystals exhibit spectral recovery under both biases, originating from self-elimination of excess electrons (negative bias) and photo-assisted elimination of trap states, whose rapid charging/discharging induces local electric field fluctuations that cause asymmetric spectral broadening (positive bias). In contrast, pure wurtzite nanocrystals allow additional hole injection, causing a reversible spectral blueshift. Under negative bias, they exhibit slow photoluminescence quenching and redshift from gradual electron injection. These differences stem from the lack of conduction band intermediate levels and a valence band barrier due to zinc blende stacking faults, suggesting microstructural engineering may enable balanced carrier injection.