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 TiO2 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 TiO2 conduction band at tower photon energies compared to QDs with adsorbed molecular dipotes which are pointing away from the QD surface (b). In US QD sensitized solar cells this leads to a dipole dependent shift of the photovoltage onset and the photocurrent.