Research On The CdS Quantum Dot Sensitized Solar Cells With SnO₂Photoanode

The development and utilization of solar energy to solve the energy crisis andthe development of low carbon economy are very important and significant. A newgeneration of solar cell—quantum dots sensitized solar cell (QDSSC) attracts muchattention owing to its high theoretical conversion efficiency and low production costs.However, the photovoltaic conversion efficiency of QDSSCs is still far lower thanconventional solar cells.It is reported that the mobility of electron in SnO2is orders of magnitude higherthan that in TiO2, further more, SnO2minimize the charge recombination underultraviolet-visible irradiation due to its larger band gap and hence has better long termstability. In this paper, the condition synthesis of SnO2with different morphologieswas investigated. The photovoltaic properties of Mn doped and undoped CdSquantum dots sensitized solar cells with prepared SnO2as photoanode were studied.experiment contents and results are listed as follows:(1) CdS quantum dots (QDs) sensitized solar cells with SnO2microspheresbased photoelectrodes are prepared. It is found that photovoltaic performance of theSnO2microspheres based photoelectrode can be obviously enhanced after TiCl4treatment. The reason is owing to the increased roughness of the film, which results inthe increased loading amounts of CdS QDs and finally improving light absorption.The electrochemical impedance spectroscopy analysis shows that the cell containingSnO2microspheres based photoelectrode with TiCl4treatment can efficiently suppressdark reaction by the increased recombination resistance. Moreover, it is found that theSnO2microspheres based photoelectrode with TiCl4treatment can increase theelectron diffusion lifetime in the cell. So after TiCl4treatment, power conversionefficiency of the cell can be increased from original1.25%to2.03%, with62.4%enhancement.(2) Mn-doped CdS quantum dot sensitized solar cells based on SnO2microspherephotoelectrodes are prepared with successive ionic layer adsorption and reaction method. It is found that with Mn-doped CdS quantum dot sensitizers, the photovoltaicperformance of the cells based on SnO2microsphere photoelectrodes can beobviously enhanced. The reasons are owing to the improved light absorption and theexpanded light absorption edge by doping Mn in CdS quantum dots. Theelectrochemical impedance spectroscopy analysis found that the cells with Mn-dopedCdS quantum dot sensitized SnO2microsphere photoelectrodes can efficientlysuppress dark reaction, owing to the increased related resistance. Moreover, it is alsofound that the Mn-doped CdS quantum dot sensitized SnO2microspherephotoelectrode can increase the electron diffusion lifetime in the cell. The powerconversion efficiency of the cell with4wt%Mn-doped CdS quantum dot sensitizerscan attain to2.80%, with53%enhancement compared with that of the CdS quantumdot sensitized cell (1.83%).(3)SnO2polyporous nanostructures particles as photoelectrodes weresuccessfully prepared by a simple and hydrothermal process with stannous chlorideas reaction precursors and without surfactant. The particles were characterized bymeans of field emission scanning electron microscopy (FESEM), field emissiontransmission electron microscopy (FETEM) and X-ray diffraction (XRD)respectively. The influence of different hydrothermal time on QDSSC photovoltaicperformance, IPCE, EIS, and UV-vis were presented. The results show that usingSnO2powder with24h hydrothermal duration in the photoanode, the powerconversion efficiency of QDSSC can attain to the highest value about2.42%.(4) Two kinds of hierarchical SnO2particles as nano-flower-like SnO2particles(NF-SnO2) and mesoporous-sphere-like SnO2particles (MS-SnO2) have beensynthesized and used in CdS quantum dots (QDs) sensitized solar cells (QDSSC).TEM images show that NF-SnO2particles compose well interconnected nanoplatesand MS-SnO2particles are consisted with large numbers of SnO2nanoparticlesabout7nm. Owing to the larger Brunauer-Emmett-Teller surface area of NF-SnO2particles, NF-SnO2photoelectrode can load higher amounts of CdS QDs and showsenhanced light absorbance, resulting in higher incident photon-to-current conversionefficiency compared with that of MS-SnO2photoelectrode. The electrochemicalimpedance spectroscopy analysis results show that the QDSSC with NF-SnO2 photoelectrode has a higher charge recombination resistance and a longer electronlifetime, so its photovoltaic performance is better than that of the QDSSC withMS-SnO2photoelectrode. The QDSSC with NF-SnO2photoelectrode can attain3%power conversion efficiency, which is higher than that of the cell with MS-SnO2photoelectrode (1.99%).