The impact of blocking layer permittivity on the electron transfer rate in quantum dot sensitized solar cells

This paper models and simulates the impact of changes in the blocking layer permittivity on the electron transfer rate (k
_ET
) from three quantum dots (QDs) of CdSe, CdS, CdTe to three metal oxides (MO) of TiO2, ZnO, SnO2 in porous-structured QDSSCs (Quantum Dot Sensitized Solar Cells) for different QD diameters and by the use of Marcus theory. Blocking layer is considered to be placed on top of QD and MO. The effective QD-blocking layer permittivity approximation is used to apply and incorporate the impacts of blocking layer to Marcus equation; changes in this equation, which is modified with respect to a new equivalent permittivity, are visible in the free energy of the system. The results show that trend of changes in k
_ET
with respect to QD diameters alters after crossing a particular permittivity threshold. For example, in TiO2-CdS and ZnO-CdS combinations, for permittivities less than 7.5, k
_ET
increases with the increase of QD diameter, but for permittivities greater than 7.5, as QD diameter increases, k
_ET
decreases. These results can be used for better interpretation of experimental observations and also in the design and selection of MO-QD combinations including the blocking layer in QDSSCs.