Preparation and ultrafast carrier dynamics of semiconductor nanoparticles

自20世纪90年代以来，利用有机染料（DSSC）吸附的纳米二氧化钛电极在太阳能电池中的应用取得了重大进展。除了有机染料外，半导体量子点（QDs）作为DSSC中的光收集器也引起了人们的兴趣。在本研究中，我们制备了不同形貌的纳米二氧化钛电极。我们将CdSe量子点吸附在电极上作为光敏剂。采用光声（PA）、光电化学电流（PEC）和瞬态光栅（TG）等方法进行表征。随着CdSe量子点吸附时间的增加，PA光谱出现了明显的红移，而PEC光谱显示了量子点吸附导致的可见光区光敏化。CdSe量子点在不同形貌的纳米TiO_2电极上的激发电子衰减时间不同，反映了CdSe量子点在不同形貌的纳米TiO_2电极上晶体生长的差异。近年来，有关Mn掺杂非晶ZnS （ZnS: Mn）的研究越来越多，部分原因是由于其高量子发光效率。我们测量了表面钝化和未钝化ZnS: Mn的PA、光致发光（PL）和PL激发（PLE）光谱。研究了紫外光照射对其PL和PLE光谱的影响。紫外照射后，ZnS: Mn的PA强度降低，表明其非辐射弛豫概率降低。观测到的PL强度增加表明辐射跃迁概率相应增加。

Significant progress in solar cell application has been made since 1990's using nanostructured TiO_2 electrodes adsorbed with organic dyes (DSSC). In addition to organic dyes, semiconductor quantum dots (QDs) have also attracted much interest as light harvesters in DSSC. In this study, we prepared nanostructured TiO_2 electrodes with different morphologies. We adsorbed CdSe QDs onto the electrodes as photosensitizers. Characterization by photoacoustic (PA), photoelectrochemical current (PEC), and transient grating (TG) methods were applied. Redshoft of the PA spectrum with the increase of CdSe QDs adsorption time can be clearly observed and the PEC spectrum showed the photosensitization in the visible region resulting from the QDs adsorption. The decay time of excited electrons in the CdSe QDs was different with each nanostructured TiO_2 electrodes with different morphologies, reflecting the difference of crystal growth of CdSe QDs on each nanostructured TiO_2 electrodes.Research involving Mn doped annocrystalline ZnS (ZnS : Mn) has grown in recent years, partly due to the high quantum luminescence efficiencies. We measured PA, photoluminescence (PL), and the PL excitation (PLE) spectra of surface-passivated and unpassivated ZnS : Mn. The effects of ultraviolet (UV) irradiation on the PL and PLE spectra were also studied. A decrease of PA intensity after UV exposure was observed for ZnS : Mn, indicating a decrease in the nonradiative relaxation probability. The observed increase in PL intensity indicates a corresponding increase in the radiative transition probability.