Enhancement of Efficiency in Quantum Dot Sensitized Solar Cells Based on CdS/CdSe/CdSeTe Heterostructure by Improving the Light Absorption in the VIS-NIR Region

In this work, we demonstrate an enhancement of photocurrent in QDSSCs based on CdS (QDs)/CdSe Quantum rods (QRs)/CdSeTe (QDs) heterostructure due to the increased photon harvesting in the VIS-NIR region. The photo-conversion efficiency increased from 2.7% up to 6.5% when CdSe QRs and CdSeTe QDs were added in the reference cell: TiO2/CdS/ZnS and the devices reached a maximum photocurrent of 21.5 mA cm−2. This outstanding performance was caused by a broadening of the light absorption in the VIS and NIR regions, this in turn, was produced by the presence of CdSe QRs and CdSeTe QDs in the cells. The use of additional SiO2 layer in the solar cell that contained CdSe QRs and CdSeTe QDs allowed us to improve the efficiency of the cells even more (up to 7.4%), since it decreased the recombination rate produced by defects and interfaces in the QDs. Moreover, the effect on the solar cells performance was studied as the size of the CdSeTe QDs introduced into them increases and found that both, the values of photocurrent and efficiency are enhanced as the size of the CdSeTe increases. We associated this improvement of performance to the increase of light absorption in the NIR region as the size of the CdSeTe QDs increases. Hence, our results suggest that the strategy of adding CdSeTe QDs with different sizes together with CdSe QRs is promising to enhance the efficiency of QDSSCs.