权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Dye sensitised solar cells (DSSC)

染料敏化太阳能电池（DSSC）

基本信息

批准号：
1904842
负责人：
金额：
--
依托单位：
University College London
依托单位国家：
英国
项目类别：
Studentship
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=studentship-1904842
关键词：
Dye sensitised solar cells DSSC

项目摘要

BackgroundDye sensitised solar cells (DSSC) are one of the promising avenues that are being explored to harvest the sun's energy. They have been the subject of much research since these photovoltaic devices were first demonstrated by Grätzel & O'Regan [1] in the early 1990's. A cartoon showing how DSSC's work is shown in Fig. 1. Future improvements will come from new pairings of substrate/dye/redox couples, with TiO2 nanoparticles being the currently favoured substrate material [2].Fig 1. DSSC--Dye-sensitized solar cells: Light transmitted by the transparent electrode is absorbed by a dye (red), which coats TiO2 nanoparticles (grey). The process forms electron-hole pairs (e-/h+). Electrons travel through the TiO2 layer to one electrode as holes travel through an electrolyte (blue) to the other electrode, generating electric current.Fundamental studies aimed at achieving an atomic level understanding of the overall DSSC system have constructed models to explain transient absorption spectra for ZnO and TiO2 substrates [3]. A comparison of these two substrates is commonly made because although TiO2 has a higher efficiency, ZnO has many advantages over TiO2 in terms of the variety of nanostructures that can be synthesised. The bulk material also has higher electron mobility. Two 2016 papers describe experimental and computational studies of the commonly employed N3 dye on ZnO and TiO2 [4,5]. These papers differ in their interpretation of the superiority of TiO2 substrates over that of ZnO. In the experimental study [4], a pump probe measurement on thin films was interpreted to indicate that an interfacial electron-cation complex is formed on ZnO that slows electron injection. In contrast, the computational study predicted that the larger density of states at the conduction band edge of TiO2 is the reason for its superior performance [5]. This discrepancy points to the challenges faced in studies of these complex systems. Nevertheless, it is clear that measurements of the photodynamics hold the key to understanding charge transfer and energy dissipation in DSSC. Here we propose to investigate N3 in the gas phase and compare it to the dye dip-coated onto atomically characterised single crystal substrates of ZnO and TiO2. We will study the photodynamics using two-photon photoemission (2PPE) with variable photon energy, and with time resolved photoemission using a visible light pump and XUV probe. Both these measurements will be carried out on the fs timescale. This is a challenging and ambitious project that will provide results that will transform our understanding of DSSC functionality.Objectives1. Use 2PPE to explore the photodynamics of N3 in the gas phase and on ZnO and TiO2 and explore the role of Ti 3d band gap states in the photoexcitation.2. Use time resolved photoemission (TRPES) to follow the population and decay of the LUMO and other states in the dye as well as band gap and conduction band edge states in the substrate.MethodologyFigure 2 shows the principles of 2PPE and HHG TRPES along with sample spectra recorded in connection with our previous work related to TiO2/H2O photocatalysis. The 2PPE work allowed us to identify a photoexcitation process in addition to band gap excitation that could be important in photocatalysis [6]. This involves hydroxyl-localised excitation from band gap states to states in the conduction band region. TRPES spectra point to the rapid recombination (<50 fs) of hot electrons created by pumping the band gap states with 1 eV light. A longer component (ca. 1 ps) is also observed if the pump is band gap light (3.1 eV). This is interpreted as VB-CB exciton pair recombination. In this earlier work, 2PPE measurements were carried out at UCL, with TRPES measurements at the Artemis facility at Harwell. In the current project this would be augmented with an existing, but as yet uncommissioned HHG apparatus at UCL.

背景染料敏化太阳能电池(DSSC)是目前正在探索的获取太阳能的最有前途的途径之一。自从20世纪90年代初Grätzel&O‘Regan[1]首次展示这些光伏器件以来，它们一直是许多研究的主题。图1显示了DSC的工作原理。未来的改进将来自新的基板/染料/氧化还原电偶对，其中纳米二氧化钛是目前最受欢迎的基板材料[2]。图1.染料敏化太阳能电池：通过透明电极传输的光被一种染料(红色)吸收，染料覆盖纳米二氧化钛(灰色)。该过程形成电子-空穴对(e-/h+)。电子通过二氧化钛层到一个电极，而空穴通过电解液(蓝色)到达另一个电极，产生电流。旨在实现对整个DSSC系统的原子水平理解的基础研究已经建立了模型来解释氧化锌和二氧化钛衬底的瞬时吸收光谱[3]。人们通常会比较这两种衬底，因为尽管二氧化钛的效率更高，但就可合成的纳米结构的种类而言，氧化锌比二氧化钛有许多优势。块体材料还具有较高的电子迁移率。2016年的两篇论文描述了常用的N3染料在氧化锌和二氧化钛上的实验和计算研究[4，5]。这些论文对二氧化钛衬底相对于氧化锌衬底的优势的解释各不相同。在实验研究[4]中，对薄膜上的泵浦探针测量的解释表明，在氧化锌表面形成了一个界面电子-阳离子复合体，从而减缓了电子注入。相反，计算研究预测，二氧化钛导带边缘较大的态密度是其优异性能的原因[5]。这种差异表明了在研究这些复杂系统时所面临的挑战。然而，很明显，光动力学的测量是理解DSSC中电荷转移和能量耗散的关键。在这里，我们建议研究气相中的N3，并将其与浸渍在原子特征单晶衬底上的氧化锌和二氧化钛的染料进行比较。我们将使用可变光子能量的双光子光电子能谱(2PPE)和可见光泵浦和XUV探头的时间分辨光电子能谱来研究光动力学。这两项测量都将在飞秒时间尺度上进行。这是一个具有挑战性和雄心勃勃的项目，它将提供将改变我们对DSSC功能的理解的结果。利用2PPE研究了N3在气相以及在氧化锌和二氧化钛上的光动力学，并探讨了Ti3d带隙状态在光激发中的作用。使用时间分辨光电子能谱(TRPES)跟踪染料中LUMO和其他状态的布居和衰变，以及衬底中的带隙和导带边缘状态。方法图2显示了2PPE和HHG TRPES的原理以及与我们之前的与TiO2/H2O光催化相关的工作中记录的样品光谱。2PPE的工作使我们能够确定除了带隙激发之外的光激发过程，这在光催化中可能是重要的[6]。这涉及到从带隙状态到导带区态的羟基局域激发。TRPES光谱表明，通过用1 eV的光泵浦带隙状态而产生的热电子的快速复合(&lt；50fS)。如果泵浦是带隙光(3.1 eV)，也可以观察到较长的分量(约1ps)。这被解释为VB-CB激子对复合。在这项早期工作中，在伦敦大学学院进行了2PPE测量，在哈威尔的Artemis设施进行了TRPES测量。在目前的项目中，将利用伦敦大学学院现有的、但尚未投入使用的氢化物发生装置来加强这一点。