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Gold nanoparticles are being used in various biomedical applications due to their small size to volume ratio, extensive thermal stability, less toxic… Many different techniques e.g. chemical, photochemical reduction and electrochemical, gamma have been applied to preparing this nanoparticle. In this paper, we are developing a low-cost technique by using a common microwave system with medium power for synthesizing gold nanoparticles with using sodium citrate (Na3Ct) reduction in chloroauric acid (HAuCl4.3H2O). It was found that the comparing with normal thermal method, the reaction by the microwave irradiation was much faster. Besides, the effects the sodium citrate concentration and optical properties of gold nanoparticles were studied. The optical properties of gold nanoparticles suspension were characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV-VIS absorption spectroscopy (UV-Vis). Maximum absorbance wavelengths ( λmax ) for gold nanoparticles  are ~ 518-524 nm with the size  of 12-25 nm. The size of gold nanoparticles decreases with increasing concentration of sodium citrate. Besides, the morphology of gold nanoparticles have a spherical shape with face-centered-cubic (fcc) crystalline structure.

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In this work, quantum dots sensitized solar cells had been successfully prepared based on Cu 2 S counter electrode and TiO 2 /CdS/Cd 1−x Mn x Se/ZnS photoanode. The highest power conversion efficiency was 3.77%. Herein, we studied the degradation process of quantum dots sensitized solar cells by investigating the photocurrent-voltage (I-V) curves and electrochemical impedance spectroscopy. The results showed that there was a downward trend of the power conversion efficiency from 3.77% to 1.52%. This trend was proved by the increase of dynamic resistance, including: charge recombination resistance at counter electrode/electrolyte and FTO/TiO 2 interface ( R ct1 increased from 204.5 Ω to 780.1 Ω), charge transfer resistance within the TiO 2 film and at the TiO 2 /QDs/electrolyte interface ( R ct2 increased from 24.65 Ω to 466.7 Ω). The decreased efficiency and increased dynamic resistance might cause the quantum dots sensitized solar cell degradation.