Determination of limiting factors of photovoltaic efficiency in quantum dot sensitized solar cells: Correlation between cell performance and structural properties

Semiconductor quantum dots (QDs) are important candidates as light absorbing materials in low cost and high efficiency sensitized solar cells (SCs). We present a combination of structural, chemical, electrical, and optical characterization that provides insight to the photovoltaic efficiencies of devices formed by TiO2 electron conducting oxide network sensitized with CdSe. In devices using colloidal QDs the collection efficiency under short circuit conditions (CESCs) for photoinjected electrons is rather high (∼90%) but the photovoltaic performance is limited by the low loading of QDs into the mesoporous TiO2 structure. On the other hand, chemical bath deposited (CBD) QDSCs exhibit a remarkably high optical density, but only slightly higher short circuit current and efficiency. It is observed that CESC is ∼50% due to the high recombination rates of the closed packed QDs structure. Our results indicate routes for improvement of QDSCs performance by the increase in colloidal QDs loading and the reduction in recombination in QDs grown in situ.