Charge Trapping Dynamics in PbS Colloidal Quantum Dot Photovoltaic Devices
Charge Trapping Dynamics in PbS Colloidal Quantum Dot Photovoltaic Devices
复制标题
DOI：
10.1021/nn403190s
复制
发表时间：
2013-10-01
期刊：
影响因子：
17.1
通讯作者：
Chen, Zhuoying
中科院分区：
文献类型：
--
作者：
Bakulin, Artem A.;Neutzner, Stefanie;Chen, Zhuoying
基于溶液处理的胶体量子点（QD）的太阳能电池的效率受到器件的活性层中的不良电荷传输的限制，这源于QD表面缺陷提供的多个捕获位点。我们应用最近开发的超快电光技术，泵推光电流光谱，阐明PbS胶体量子点光伏器件在工作条件下的电荷捕获动力学。我们发现量子点在0.2-05 eV区域的红外光诱导吸收部分与不动电荷有关，这些电荷在我们的实验中可以被光学解陷。使用这种吸收作为探针，我们观察到，早期的捕获动力学强烈依赖于用于量子点钝化的配体的性质，而它只轻微依赖于电子接受层的性质。我们发现，弱束缚态，具有0.2 eV的光子激活能，填充瞬间光激发。这表明光生态显示出固有的束缚态特征，可以说类似于有机光伏材料中的电荷转移态形成。在类似于0.1-10 ns的时间尺度上观察到较深陷阱（激活能03-05 eV）的顺序布居，表明大部分载流子捕获仅发生在实质性电荷弛豫/传输之后。报道的研究从根本上解开不同的贡献，电荷捕获动力学的纳米晶为基础的光电器件，可以作为一个有用的工具，量子点太阳能电池的发展。
The efficiency of solution-processed colloidal quantum dot (QD) based solar cells is limited by poor charge transport in the active layer of the device, which originates from multiple trapping sites provided by QD surface defects. We apply a recently developed ultrafast electro-optical technique, pump-push photocurrent spectroscopy, to elucidate the charge trapping dynamics in PbS colloidal-QD photovoltaic devices at working conditions. We show that IR photoinduced absorption of QD in the 0.2-05 eV region is partly associated with immobile charges, which can be optically detrapped in our experiment. Using this absorption as a probe, we observe that the early trapping dynamics strongly depend on the nature of the ligands used for QD passivation, while it depends only slightly on the nature of the electron-accepting layer. We find that weakly bound states, with a photon-activation energy of 0.2 eV, are populated instantaneously upon photoexcitation. This indicates that the photogenerated states show an intrinsically bound-state character, arguably similar to charge-transfer states formation in organic photovoltaic materials. Sequential population of deeper traps (activation energy 03-05 eV) is observed on the similar to 0.1-10 ns time scales, indicating that most of carrier trapping occurs only after substantial charge relaxation/transport. The reported study disentangles fundamentally different contributions to charge trapping dynamics in the nanocrystal-based optoelectronic devices and can serve as a useful tool for QD solar cell development.