Invited Paper EH-ThM1
Improving the Photoconversion Efficiency of Quantum Dots Sensitized TiO2 Solar Cells Prepared by SILAR and Electrophoresis Method

Thursday, December 11, 2014, 8:00 am, Room Lehua

One of the most studied hybrid-type nanostructured solar cells is the Gratzel or dye sensitized solar cell (DSSC). DSSCs typically consist of TiO₂ NCs acting as a highly porous, wide bandgap semiconductor for electron collection, and dye molecules adsorbed onto the TiO₂ NCs surface acting as sensitizers to harvest solar light. An alternative to DSSC is the utilization of quantum dots (QDs), e.g., CdSe, CdTe, CdS, PbS, PbSe, Bi2S3, and InP, as sensitizers to replace the expensive ruthenium dyes. QDs have large extinction coefficients in the visible region and, after bandgap excitation, undergo charge separation, injecting electrons to the conduction band of the metal oxide

The quantum dots (QD) has been recently drawing great attention as a material for solar energy conversion. The quantum dots sensitized titanium dioxide (TiO₂) was synthesized by different chemical methods such as successive ionic layer adsorption and reaction (SILAR), and electrophoresis (EP). Titanium dioxide (TiO2) films consisting of a 150 nm compact layer, a 6 µm layer made of 40 nm TiO₂ nanoparticles (NPs) and a 7 µm scattering layer made of 400 nm TiO₂ NPs, were composited with several QDs such as CdS, PbS, ZnS, and Bi₂S₃ by SILAR and EP. Multisensitized configurations as PbS/CdS/ZnS and CdS/Bi₂S₃/Zns were analyzed obtaining a photoconversion efficiencies of 3.75% and 2.52% respectively. These efficiencies are due to high photocurrents (14.3 and 10.2 Ma/cm², respectively) obtained by the correct combination of near infrared and visible light photoabsorption. Photoconversion efficiency was increased to 5% by combining both sensitizers method in the appropriate way. It also was studied the effect of depositing Gold Nanoparticles (Au NPs) by electophoresis in CdS SILAR sensitized solar cells, results show that Au NPs slightly reduces the photocurrent (from 8.7 to 7.4 Ma) by reducing the photoabsoption of the CdS QDs, but at the same time strongly increases the FF (from 51 to 58%) and Voc (from 510 to 560 Mv). Electrochemical measurements suggest that Au NPs help to prevent recombination processes in the solar cell. In this paper, a detailed analysis of charge transport on both configurations is presented; taking advantage of impedance spectroscopy (IES) a detailed analysis of each interface is also presented.