Quantum dot sensitized solar cells (QDSSCs) are considered to be a simple analogue of dye sensitized solar cells (DSSCs). The only apparent difference involves the replacement of the organometallic or organic dyes with QD sensitizers such as CdS, CdSe, PbS, PbSe and InP. Otherwise, the basic cell mechanisms – including charge separation by the sensitizer, charge transport in both the mesoporous electrode and the electrolyte, and the recombination paths – seem to be similar to those of DSSCs. The replacement of dye sensitizers by QDs is motivated by their absorption coefficient, which is higher than in most dyes, and the doping capabilities and size confinement that allow energetic alignment and tailoring of the effective absorption spectrum. Moreover, the use of QDs opens new possibilities for third generation solar cell configurations such as multiple electron generation (MEG) and hot electron injection. Consequently, in the last three years we note a significant increase in the conversion efficiencies of QDSSCs towards the standard values of the DSSC analogue.

Recently we reported on unpredicted electron injection from CdSe-QD to nanoporous ZrO2 electrodes. A study of quantum-rod sensitized solar cells revealed dipole formation along the rods and a consequent improvement in performance. A systematic optimization of the QD layer thickness suggested new design rules for QDSSCs. Work on pure QD based photoelectrochemical, tandem solar cells, in which a QD layer is deposited directly on FTO glass, enabled direct photoelectrochemical study of the QDs without the interference of the mesoporous TiO2 electrode. We showed that a solar cell based solely on QDs can generate photovoltaic activity when immersed in a polysulfide electrolyte. Advanced characterization, utilizing charge extraction and open circuit voltage (Voc) decay techniques, quantified the charge accumulated in the QD layer and the rate at which it recombines with the surrounding electrolyte. Consequently, this set of results provide new insight to a fundamental difference between DSSC and QDSSC, which is critical for further improvement of QD sensitized solar cells.

Based on the unique operating mechanism of QDSSCs, we developed new materials and methods to improve their performance. We will report on new wide bandgap electrodes, recombination blocking layers and photo induced energetic alignment within the cell.