In this study, we focus on the enhanced absorption and reduced recombination of quantum dot solar cells based on photoanodes which were coated by different ZnS or SiO 2 passivations using the successive ionic layer absorption and reaction methods. The quantum dot solar cells based on photoanode multilayers, which were coated with a ZnS or SiO 2 passivation, increased dramatic absorption in the visible light region as compared with other photoanodes and reduced rapid recombination proccesses in photovoltaic. As a result, the performance efficiency of TiO 2 /CdS/CdSe photoanode with SiO 2 passivation increased by 150% and 375% compared with TiO 2 /CdS/CdSe with ZnS passivation and TiO 2 /CdSe photoanode, respectively. For this reason, we note that the tandem multilayers can absorb more wavelengths in the visible light region to increase a large amount of excited electrons, which are transferred into the TiO 2 conduction band, and decrease number of electrons returned to the polysulfide electrolyte from QDs when a ZnS or SiO 2 passivation is consumed. Moreover, it is obvious that there was a far shift towards long waves in UV-Vis spectra and a sharp drop of intensity in photoluminescence spectra. In addition, the dynamic process in solar cells was carried out by electrochemical impedance spectra.

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In this work, quantum dots sensitized solar cells had been successfully prepared based on Cu 2 S counter electrode and TiO 2 /CdS/Cd 1−x Mn x Se/ZnS photoanode. The highest power conversion efficiency was 3.77%. Herein, we studied the degradation process of quantum dots sensitized solar cells by investigating the photocurrent-voltage (I-V) curves and electrochemical impedance spectroscopy. The results showed that there was a downward trend of the power conversion efficiency from 3.77% to 1.52%. This trend was proved by the increase of dynamic resistance, including: charge recombination resistance at counter electrode/electrolyte and FTO/TiO 2 interface ( R ct1 increased from 204.5 Ω to 780.1 Ω), charge transfer resistance within the TiO 2 film and at the TiO 2 /QDs/electrolyte interface ( R ct2 increased from 24.65 Ω to 466.7 Ω). The decreased efficiency and increased dynamic resistance might cause the quantum dots sensitized solar cell degradation.