| Quantum dot-sensitized solar cells is one of the third generation solar cells. Benefited from the adjustable spectral response, high extinction coefficient and high theoretical conversion limit, Quantum dot-sensitized solar cells has become an important and promising research direction of the solar cells. Although, the conversion efficiency of quantum dot-sensitized solar cells is still far behind from those of conventional solar cells so far. Based on this situation, we have managed to make improvement of the quantum dot-sensitized solar cells from following aspects:increasing quantum dots loading on photoanode, optimizing quantum dots composition and fabrication of high catalytic counter electrodes.First of all, based on the fact that the adsorption of as-prepared quantum-dots to the TiO2 photoanode is quite low, we have dipped into the adsorption mechanism of aqueous quantum-dots on TiO2 photoanode and proposed a new theory of adsorbing quantum-dots under strong alkali conditions. Practically, we have successfully improved the actual CdTe quantum dots loading amount as well as the CdTe quantum dots surface modifications through this strong alkali adsorption theory. This theory can be simply explained from the contributions of Na+and OH- respectively. On one hand, Na+mainly suppress electrostatic repulsion between quantum dots and TiO2 to improve the chances of quantum dots adsorption. OH-,on the other hand,maintain surface modifications of the quantum dots during the adsorption process In the meantime, strong alkali conditions will induce a thin Cd(OH)2 formation on CdTe quantum-dot surface to improved photo stability of quantum-dots. In all, The overall efficiency of CdTe a sensitized cells is increased by nearly 40 percent of which is more than 2% at AM1.5 conditionsMeanwhile, in order to solve Pt cathode poisoning problem when catalyzing polusulfide electrolyte, metal selenide have been altered to replace Pt cathode. In the 3rd chapter, we have raised a new facile route to fabricate Cu2-xSe cathode based on rough copper substrate. After optimizing the catalysis behavior of Cu2-xSe from HCl concentration, reaction temperature and time, the final catalytic resistance of the Cu2-xSe achieved can be as low as about 0.85Q/cm2 from simply immersing etched copper into NaHSe-NaOH solution for certain period of time. When coupled to CdSeS sensitized solar cells as counter electrode, the overall conversion efficiency of the cell can be 3.7%.For cuprous selenide can better catalyze polysulfide electrolyte than Pt, we have managed to develope a novel red-selenium induced formation of CuxSe on conductive glass substrate. In this route, neither additional vaccum nor backup structure is needed to fabricate CuxSe counter electrode with relatively high specific area and a desired depth. And the fimal catalytic resistance can be minimized to 0.79Ω/cm2. Coupled with this counter electrode, the reduction of output photocurrent is less than 5% even after 1 hour under consecutive 1 sun expose.We then switched the investigation to alloyed quantum-dots CdSexTe1-x instead of CdTe quantum dots. By controlling the ratio of Se:Te and other factors in quantum-dot nuclei and growth, we can get CdSexTe1-x quantum-dots with good qualities as sensitizers for solar cell assembly. The cell photochemical and Ⅰ-Ⅴ measurement shows that when the ratio of Se:Te is set at 0.4, the overall efficiency is the highest,2.47%, an 90% and 70% increase from those of CdSe and CdTe sensitized solar cells respectively. Furthermore, we have also ehanced the fill factors of solar cells through providing better surface-modified quantum-dot and achieved a relatively high fill factor of 0.72. Although the actual short-circuit current dropped slightly, the much higher fill factor leads to an overall conversion efficiency of 3.02% using aqueous polysulfide electrolyte. |
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