CdSe量子点敏化纳米二氧化钛太阳电池的电化学交流阻抗谱

Electrochemical impedance spectra of CdSe quantume dots sensitized nanocrystalline TiO_2 solar cells

量子点敏化纳米TiO2太阳电池(QDSSCs)具有诱人的发展前景,但是与传统的染料敏化太阳电池(DSSCs)相比,其目前的光电转换效率还非常低(仅为3%左右).为了寻找QDSSCs光电转换效率低的原因,本文主要采用外加偏压下的交流阻抗谱技术对通常以S2-/Sx-离子对为电解质的CdSe胶体量子点敏化纳米TiO2电极的准费米能级、电子传输复合特性以及串联电阻等问题进行了考察,并将之与以I-/I3-离子对为电解质的DSSCs的测试结果进行了对比分析.从纳米TiO2膜层的化学电容曲线可以看出,QDSSCs中电解液电子费米能级与纳米TiO2导带边的能量差比DSSCs中的小约0.3V,是QDSSCs开路电压比DSSCs低约0.3V的主要原因.铂电极/电解质界面电荷转移电阻和电解质对扩散电阻相对较大,引起较大的串联电阻,是QDSSCs填充因子低的主要原因.另一方面,QDSSCs的暗态电子寿命和电子扩散长度比DSSCs略大,可以认为纳米TiO2表面吸附的双功能耦联剂在一定程度上抑制了纳米TiO2/电解质界面的电子复合,说明目前采用胶体量子点自组装方法制备的QDSSCs短路电流低的主要原因不是纳米TiO2/电解质界面电子复合.进一步提高光吸收效率和光电子注入效率是提高该类QDSSCs光电转换效率的主要方向之一.

Quantum dots sensitized nanocrystalline TiO2 solar cells （QDSSCs） are promising third-generation photovoltaic devices. In comparison with conventional dye-sensitized solar cells （DSSCs）, the efficiency of QDSSCs is still very low （about 3%）. In this paper, the electrochemical impedance spectroscopy technology has been adopted to investigate the quasi-Fermi level and the cartier dynamics of the colloidal CdSe QDs sensitized TiO2 eletrode with S^2-/Sx redox electrolytes and the series resistance of the QDSSCs. In comparison with the conventional DSSCs with I^3-/I^- as redox electrolytes, the energy difference between the conduction band edge and the quasi-Fermi levels of the TiO2 films for the Fermi levels of the redox electrolytes） in QDSSCs has been decreased by about 0.3 V, resulting in the decrease of Voc by this value. The increases of the electrolyte diffussion resistance and the charge transfer resistance between Pt counter electrodes and S^2-/Sx redox electrolytes were attributed to the decrease of the fill factors. However, the electron lifetime and electron diffussion length for QDSSCs are longer than those for DSSCs due to the retardation of the electron recombination by the adorbed cysteine at the surfaces of the TiO2 films. It is indicated that electron recombination at the TiO2/electrolyte interface is not the main reason for the lower Jsc of the colloidal QDs sensitized QDSSCs. Improving light harvesting efficiency and photoelectron injection efficiency should be considered in the future for such kind of QDSSCs.