Nanostructured Materials and Devices Group, Department of Chemistry, Imperial College London, SW7 2AZ, United Kingdom.
J Am Chem Soc. 2010 Mar 3;132(8):2743-50. doi: 10.1021/ja909172p.
We report a transient absorption and luminescence study addressing the charge separation, recombination, and regeneration reactions at nanostructured metal oxide/PbS quantum dot/organic hole conductor heterojunctions. We show that yields of charge separation are significantly higher at PbS/SnO(2) interfaces relative to PbS/TiO(2) interfaces, and conclude that this behavior is a result of the ca. 300-500 meV lower conduction band edge in SnO(2) as compared to TiO(2). We also report a correlation between the PbS particle size and the yield of charge separation at PbS/SnO(2) interfaces, with a smaller PbS particle radius resulting a higher yield of charge separation. Finally we investigated the regeneration of the photooxidized PbS by an organic hole transporting material, namely, spiro-OMeTAD. The overall spiro-OMeTAD(+) yield is found to be 27% at a SnO(2)/PbS (approximately 3 nm diameter)/spiro-OMeTAD heterojunction. The addition of a lithium salt was found to raise the overall spiro-OMeTAD(+) yield from its initial value of 27% (where no Li(+) is present) to 50%. We believe this to be a result of an increase in the primary charge injection yield to near unity as the SnO(2) conduction band is lowered (with increasing [Li(+)]), increasing the driving force for electron injection. The present findings are discussed with relevance to the design of PbS-sensitized metal oxide layers for DSSCs.
我们报告了一项瞬态吸收和发光研究，该研究涉及纳米结构金属氧化物/PbS 量子点/有机空穴传输体异质结中的电荷分离、复合和再生成反应。我们表明，PbS/SnO2 界面的电荷分离产率明显高于 PbS/TiO2 界面，并且得出结论，这种行为是由于 SnO2 的导带边缘比 TiO2 低约 300-500 meV。我们还报告了 PbS/SnO2 界面处 PbS 颗粒尺寸与电荷分离产率之间的相关性，较小的 PbS 颗粒半径导致更高的电荷分离产率。最后，我们研究了光氧化的 PbS 通过有机空穴传输材料（即 spiro-OMeTAD）的再生成。在 SnO2/PbS（约 3nm 直径）/spiro-OMeTAD 异质结中，发现 spiro-OMeTAD(+)的总产率为 27%。添加锂盐被发现将 spiro-OMeTAD(+)的总产率从初始值 27%（不存在 Li(+)）提高到 50%。我们认为这是由于 SnO2 导带降低（随着[Li(+)]的增加），导致初始电荷注入产率接近 1，从而增加了电子注入的驱动力。本研究结果与设计用于 DSSC 的 PbS 敏化金属氧化物层有关。
