| Sensitized solar cells have attracted much attention due to low cost, ease of preparation and high theory photoelectric conversion efficiency. The major styles of sensitized solar cells are dye-sensitized solar cells (DSSC) and quantum dots sensitized solar cells (QDSSC). However, the poor transport rate of photoelectrons, low light harvesting efficiency and inferior adsorption of dye and quantum dots limit the development of sensitized solar cells. This project focuses on the modification of the photoanode. The major work includes preparation of branched TiO2 nanostructure, modification branched TiO2 nanostructure with various content of Ag nanoparticles (NPs), introduction of cap layer to build double layer structure. All of these photoanodes are sensitized, sealed and then measured for further investigation of the mechanism. The corresponding experimental results are summarized as follows:(1) The synthesis of branched TiO2 nanorods (BTNR) involves hydrothermal growth of rutile TiO2 nanorods (TNR) on FTO substrate and following by immersing the TiO2 nanorods into TiO2 solution to form rutile branches. It comes to a conclusion that the power conversion efficiency (PCE) of BTNR/N719 cell is 133% higher than that of TNR/N719 cell, the PCE of BTNR/CdS cell is 66.7% higher than that of TNR/CdS cell, the PCE of BTNR/CdS/N719 cell is 177% higher than that of TNR/CdS/N719 cell. All of these results demonstrate that BTNR photoanode presents superior properties to TNR photoanode.(2) Ag NPs modified BTNR photoanode (BTNR/Ag) in a gradient is synthesized by photoreduction method. By controlling the concentration of AgNO3 solution, BTNR/Ag photoanodes with different Ag content are dye-sensitized for further investigation of photovoltaic properties. It is discovered that the highest photovoltaic performance is obtained in BTNR/Ag3 photoanode, the corresponding PCE achieves 2.9%, which is 43.6% higher than BTNR photoanode (1.96%). It is suggested the superior photovoltaic performance of BTNR/Ag3 photoanode is mainly due to the enhanced light harvesting efficiency and charge carrier recombination which is highly dependent on the content of Ag NPs in the films:(1) the plasmon-enhanced light absorption caused by small-scale Ag NPs close to the FTO substrate, (2) the improved scattering ability of photoanode arosed from large-scale Ag NPs near the top, (3) the dye molecules increase with the increased surface area caused by the introduction of Ag NPs, (4) lower recombination due to the schottky barrier between Ag and BTNR. However, as the content of Ag surpass the optimum value, such as BTNR/Ag4 (2.03%), the photovoltaic performance turns inferior due to more recombination of carriers.(3) TiO2 hollow spheres (THS) and CdS hollow spheres (CHS) are synthesized by hard template method and used as cap layer on TiO2 nanoparticles (TP) to form double layer structure of TP/THS and TP/CHS photoanode in QDSSC. Our group explores the role of CHS cap layer in the TP/CHS photoanode and its effect to the photovoltaic performance of TP/CHS/CdS cell by comparing with the pure TP/CdS cell and TP/THS/CdS cell. The result shows that the Jsc of TP/CHS/CdS cell is 8.21 mA·cm-2, which is much higher than 4.52 mA·cm-2 of TP/CdS cell and a little more than 7.61 mA·cm-2 of TP/THS/CdS cell. The PCE of TP/CHS/CdS cell is 2.28%, higher than that of TP/THS/CdS cell (2.04%) and TP/CdS cell (1.16%). For TP/THS photoanode, the improvement in PCE is mainly due to the enhanced scattering property. For TP/CHS photoanode, the major reason can be ascribed to:(1) enhanced scattering ability; (2) improved light absorbance by CdS; (3) fast transport rate of electrons and low recombination rate. Therefore, the TP/CHS photoanode exhibit superior photovoltaic performance to TP/THS photoanode. |
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