Influence Of Ⅱ-Ⅵ Quantum Dots And The Morphologies Of Photoanodes On The Photovoltaic Performence Of Quantum Dot Sensitized Solar Cell

Due to the global environment pollution and impending exhaustion of fossil fuels, thedevelopment of solar cell industry is faster. Although silicon solar cells with high performancehave shared over ninety percent of the solar cell market, additional subsidies from nationalgovernment are still needed for large-area utilization due to the high cost. Moreover, thetraditional silicon solar cell industries in China are experiencing "double reverse" tradesanctions, which makes them more difficulty to survive. A possible way to solve thecontradiction between their performance and cost is to develop novel solar cells usingnanomaterials and nanotechnology with new characteristics, which is different from thetraditional bulk or thin film cells. Inorganic oxides are usually green and abundantsemiconductors and can be used to fabricate solar cells with low cost.In this thesis, the quantum dot sensitized solar cell （QDSSC） was slected as the researchobject. Titanium dioxide （TiO₂） mesoporous thin films and zinc oxide （ZnO） nanowires arrayswere adopted as photoanodes to study the influence of morphology on the electrical transportproperties of photo-carriers. Ⅱ-Ⅵ compound quantum dots were used as light absorbers tostudy the influence of bandgap effect caused by QD composition on the generation andinjection of photo-carriers. The main research contents and results are as follows.1. TiO₂mesoporous thin film photoanodes were fabricated by screen-printing technology.The prefered properties of photoanodes like no delamination, high transparent andmanageable uniform thickness were obtained by optimizing the screen-printing conditions,which is the first step for assembling QDSSC.2. CdTe and ternary alloyed HgCdTe quantum dots coated with thioglycolic acid weresynthesized by using aqueous phase method and their application as light absorber forQDSSC was dmonstrated. The absorption and photoluminescence properties of CdTequantum dots doped with Hg were studied and the doping mechanism was explained. Inaddition, CdTe sensitized TiO₂mesoporous film solar cell show low efficiency due to smallQD absorption. Another reson is the TAG coating of CdTe QDs results in inefficient carrierinjection from QDs to photoanode. 3. Conformal and uniform CdS/CdSe quantum dots were prepared on the surface of TiO₂mesoporous films by a series of successive ionic layer adsorption and reaction （SILAR）processes. The numbers of SILAR cycles has important influences on the absorption propertyof photo-anode and the corresponding photovoltaic performance of solar cells. In addition,due to the low electron mobility of polycrystalline TiO₂mesoporous films, it is an effectiveway to further improve the power conversion efficiency of solar cell by choosing thephoto-anode with high electron mobility.4. Conformal ZnO/CdS and ZnO/CdS_xSe_1-xcore/shell nanocables were grown by ionexchange reaction method. Due to the partial conversion of CdS to CdSe, the spectralresponse range of photo-anode were extended, which improved the power conversionefficiency of solar cell. But the power conversion efficiency of solar cell was limited by thecorrosion in an alkaline solution and the defects in quantum dots shell. This work needsfurther study.5. The problem that nanorods partially peelled from the FTO substrate due to thecorrosion caused by an alkaline solution has been resolved by the deposition of AZO seedlayer. And then, the influences of ZnO/CdS_xSe_1-xtreated with rapid thermal annealing on theperformance of solar cell were systematically researched. The crystal quality of ZnO/CdS_0.33Se_0.67was improved at200℃, which can reduce the electronic-hole recombinationprobability in photo-anode. With the increase of annealing temperature from300℃to400℃,the size of quantum dots growed up, which expanded the spectral response range; in addition,due to the decrease of the interfacial electron transfer resistance, the open circuit voltageincreased and the highest cell efficiency was obtained at400℃. To further inscrease theannealing temperature to500℃, the formation of CdS_0.33Se_0.67solid solution led to theabsorption blue shift of quantum dots layer.