228 Hydrothermal growth of TiO 2 nanorods on the nanocrystalline TiO2 layer and their application in ZnS and SiO2 passivated photoanode of CdS sensitized solar cells.

In this research TiO2 nanorods were grown on the surface of TiO2 nanocrystalline layers and applied in the ZnS and SiO2 passivated photoanode of CdS sensitized solar cells. In the st first part of experiments, TiO2 nanoparticles were prepared by hydrothermal methods in an acidic medium using titanium tetraisopropoxide (TTIP) as the Ti precursor. Then, a layer of theses nanoparticles was deposited on FTO glass substrates with 6-μm thickness. This layer was called as H1 and was sensitized with CdS quantum dots through the successive ionic layer adsorption and reaction (SILAR) process. For improving the photovoltaic performance of quantum dot sensitized solar cells (QDSCs), the photoelectrodes were coated with four cycles of ZnS by immersing in 0.1 M, Zn(OAc)2 and 0.1 M, Na2S aqueous solutions for two successive 1 min. Then they were coated with SiO2 layer by soaking the electrodes in 0.01 M tetraethyl orthosilicate ethanol solution for 1 h followed by rinsing with ethanol and drying in air [1]. The two ZnS and SiO2 nanocrystalls layers were also deposited as the electron blocking components to decrease the unwanted e-h recombinations. The results show that the QDSC with a photoanode sensitized through 4 cycles of CdS deposition and passivated with ZnS/SiO2 layers represents the Jsc of 7.18 mA/Cm2, Voc of 634 mV and energy conversion efficiency of 2.21% (Fig.1a). This efficiency was increased about 78.2% compared to that of the reference cell with H1/CdS/ZnS Photoelectrode. In the second part of experiments, TiO2 nanorods were grown on H1 layer by hydrothermal method with titanium tetra-butyl titanate as the Ti precursor. This bi-layer was named as the H1/INRs and was analyzed for the surface morphology. Fig. 2(a, b) demonstrate the top view and cross-sectional SEM images the H1/INRs layer. According to the images the inclined TiO2 nanorods were grown on the surface of TiO2 NCs layer. The diameter and length of the NRs were about 75 nm and 2 μm. respectively. The thickness of TiO2 NRs layer was also measured about 1.9 μm. The photoelectrodes were similarly sensitized with CdS NCs using 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 229 SILAR method. The ZnS and SiO2 blocking layers were also over-deposited on the photoanodes surface for better photovoltaic performance. The results demonstrated that the QDSC with a photoelectrode sensitized through 4 cycles of CdS deposition and passivated with 4 cycles of the ZnS formation represents a Jsc of 11.25 mA/cm2, Voc of 586 mV and energy conversion efficiency of 3.04% (Fig 3). This efficiency was improved about 13.43% compared to that of the reference cell with H1/INR/CdS/ZnS` photoelectrode.