Illumination Intensity-Dependent Electronic Properties in Quantum Dot Sensitized Solar Cells

New results of photoelectrochemical solar cells that consist of quantum dots (QDs) deposited directly onto FTO glass identify chemical potential within the QD layer as the source for the observed photovoltage. Charge extraction and transient photovoltage measurements of this cell quantify the lifetime and density of the photogenerated electrons within the QDs layer. At open circuit voltage, the electron density approaches 1 × 1019/cm3, which corresponds to one electron per dot. The electron lifetime varies from 10 ms at low photovoltage to 0.1 ms at open circuit. These results lead to new understanding of the photoelectrochemical mechanisms in quantum dot sensitized solar cell. Under illumination, the QD sensitizer layer can charge up to levels that alter the relative energetics within the cell thus affecting both the generation and recombination mechanisms. The new insight, identifying a conceptual difference between QD and dye-sensitized solar cells, opens new paths for improvement and optimization of QD sensitized solar cell.