| Nanocrystal solar cells combine low-cost solution processibility and all inorganic structure with good chemical stability and flexible structure. CdTe and PbS nanocrystals can be synthesized by a simple solvent-thermal method. They can disperse in a solvent with the help of surface ligands, and can change into smooth film by spin coating. They have appropriate band gap and high absorption coefficient, which is very suitable for photovoltaic devices. The energy conversion efficiency of CdTe nanocrystal solar cells and PbS quantum dot solar cells have exceeded 10%. There are many routes to improve the performance, including improving the quality of the materials, optimizing the deposition process and optimizing the device structure. This paper focuses on CdTe and PbS nanocrystals. On the basis of previous work, we prepared the alloy nanocrystals with different components successfully by adjusting the composition ratio of Se and Te in the precursor; and we prepared high quality PbS nanocrystals by a solvent-thermal method. PbS quantum dot solar cells have been fabricated, and the effect on the properties of the solvent engineering PbS quantum dots thin film has been studied in detail. The main research work includes the following aspects:Firstly, CdSexTe1-x alloy nanocrystals were synthesized by solvent thermal method and pre blending TOP-Se and TOP-Te precursors. We studied he composition and morphology of the nanocrystals and the relationship between TOP-Se and TOP-Te volume ratio in the precursor and Se:(Se+Te) atomic percentage in the nanocrystals. The band gap of nanocrystals was tested by optical and electrochemical methods, and the relationship between the composition and the band gap was studied. The study shows that the atoms percentage of Se:(Se+Te) in the alloy nanocrystals is controlled by the volume ratio of TOP-Se and TOP-Te in the precursor. The nanocrystal is composed of CdTe and CdSe with wurtzite structure. With the increase of Se content, the size and the draw ratio of the nanocrystals decreased, and the size distribution becomes wider. The band gap of CdSexTe1-x nanocrystals decreases with the increase of Se content in the known range, and presents a nonlinear relationship. The optical band gaps of CdTe, CdSe0.10Te0.90, CdSe0.19Te0.81, CdSe0.36Te0.64 were 1.69 eV, 1.66 eV, 1.61 e V, 1.54 eV respectively.Secondly, we used octane, isooctane, heptane, hexane and toluene as solvents to dissolve PbS nanocrystals and studied the relationship between film morphology and polarity, viscosity and boiling point of the solvent. Further, the effect of the mixed solvent on the morphology of the film and the power conversion efficiency(PCE) and stability of the device was studied by mixing the two solvents in a certain proportion. The research shows that solvents with higher boiling point, such as octane and toluene, can make the film smooth. Mixed solvents can increase PCE of PbS quantum dot solar cells. PCE of 7.64% was obtained by using the mixed solvent of 5% isooctane and 95% octane. All PbS quantum dot solar cells with different solvents have good stability. Among them, a device with toluene as the solvent still has a PCE of 6.18% after 150 days of storage, with no significant decline.Thirdly, AZO thin films with crater morphology were prepared by a simple chemical wet etching method. We studied the effect of etching time on the morphology of the films systematically. We tested light trapping property of surface textured AZO and fabricated PbS quantum dots heterojunction solar cells with light trapping structure. The study shows that with the increase of etching time there are larger but less craters on the AZO. When etching time is 20 s, 25 s, 30 s, 35 s, the AZO films has regularly distributed craters with opening angles between 115°and 131°which are very effective in light scattering. When etching time is 30 s, the AZO film has the best light-trapping ability, which effectively increases the absorption in PbS quantum dots film. |
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