Energy Level Alignment in CdS Quantum Dot Sensitized Solar Cells Using Molecular Dipoles

The energy levels of CdS quantum dots (QDs) can be shifted in a systematic fashion with respect to the TiO(2) bands using molecular dipoles. Dipole moments pointing toward the QD surface shift the energy levels toward the vacuum level (a), thus enabling electron injection from excited QD states into the TiO(2) conduction band at lower photon energies compared to QDs with adsorbed molecular dipoles which are pointing away from the QD surface (b). In CdS QD sensitized solar cells this leads to a dipole dependent shift of the photovoltage onset and the photocurrent.