Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
J Am Chem Soc. 2013 Aug 7;135(31):11461-4. doi: 10.1021/ja405026x. Epub 2013 Jul 25.
In quantum dot (QD) sensitized solar cells (QDSSCs), redox electrolytes act as hole scavengers to regenerate the QD ground state from its oxidized form, thus enabling a continuous device operation. However, unlike molecular sensitizers, QDs also have redox-active trap states within the band gap, which can be charged in the presence of redox electrolyte. The effects of electrolyte induced charging of QDs on the performance of QDSSCs have not been reported. Here, using steady-state and time-resolved absorption and emission spectroscopy, we show that CdSe/CdS3MLZnCdS2MLZnS2ML core/multishell QDs are charged in the presence of sulfide electrolytes due to the reduction of surface states. As a result, exciton lifetimes in these QDs are shortened due to an Auger recombination process. Such charging induced fast Auger recombination can compete effectively with electron transfer from QDs to TiO2 and reduce the electron injection efficiency in QDSSCs. We believe that the reported charging effects are present for most colloidal nanocrystals in the presence of redox media and have important implications for designing QD-based photovoltaic and photocatalytic devices.
在量子点敏化太阳能电池（QDSSCs）中，氧化还原电解质作为空穴捕获剂，将 QD 的基态从其氧化形式中再生，从而实现连续的器件操作。然而，与分子敏化剂不同，QD 也在带隙内具有氧化还原活性的陷阱态，在氧化还原电解质存在的情况下可以被充电。电解质诱导的 QD 充电对 QDSSCs 性能的影响尚未有报道。在这里，我们使用稳态和时间分辨吸收和发射光谱，表明 CdSe/CdS3MLZnCdS2MLZnS2ML 核/多壳 QD 在硫化物电解质存在下会因表面态的还原而被充电。结果，由于俄歇复合过程，这些 QD 中的激子寿命缩短。这种充电诱导的快速俄歇复合可以有效地与 QD 向 TiO2 的电子转移竞争，并降低 QDSSCs 中的电子注入效率。我们相信，在存在氧化还原介质的情况下，大多数胶体纳米晶体都存在报告的充电效应，这对设计基于 QD 的光伏和光催化器件具有重要意义。
