Hot charge carriers in quantum dot-based electron transfer systems for application in photovoltaics

光伏应用中基于量子点的电子转移系统中的热载流子

• 批准号: 262584021
• 负责人: Professor Dr. Josef Wachtveitl
• 金额: --
• 依托单位: Institut für Physikalische und Theoretische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/262584021?language=en
• 关键词: Hot; charge; carriers; quantum; dot

Low-cost solar cells as an alternative to the widely used silicon-based photovoltaic (PV) devices have attracted immense interest during the past decades. In this field the dye sensitized solar cell (DSSC), with a molecular dye as light absorber, reaches a conversion efficiency of 11.9% with an electron transfer (ET) time on the femtosecond time scale. Inspired by the DSSC the quantum dot solar cell (QDSC) has been developed where the light harvesting is achieved by semiconductor quantum dots (QD). QD exhibit robustness against photodegradation, large extinction coefficients down to the near infrared and the mechanism of carrier multiplication. Main obstacles towards higher conversion efficiencies of QDSCs are sub-band gap states acting as charge traps and nonradiative surface recombination processes because of a large surface-to-volume ratio of QD. An alternative to the semiconductor QD are metal QD (Au, Ag, Cu) performing a plasmon-induced ET to TiO2.The previous project aimed for charge and energy transfer processes in QD-molecular acceptor assemblies with focus on charge separating heterostructures and hot charge carriers. Furthermore, the photoinduced ET and coherent phenomena at the dye/semiconductor interface have been successfully examined. In line with the first funding period we will investigate charge separating heterostructures and focus on the separation of multiexcitons with particular emphasis on the shell effect. Furthermore, the QD intrinsic charge separation dynamics of holes (core) and electrons (shell) will be manipulated by a spacing, large band gap intershell (onion-like QD). By variation of the intershell thickness the electronic coupling between core and shell should be modified leading to different charge separation dynamics. We already implemented a NIR transient absorption set-up, successfully synthesized colloidal PbS QD which are particularly interesting for PV applications and started the spectroscopic characterization. We will test the ET dynamics of systems containing PbS QD and molecular electron acceptors, and quickly move on to the investigation of PbS QD directly grown on the surface of metal oxide thin films. To avoid toxic elements of the standard semiconductor QD, metal QD can serve as an alternative. We will investigate surface plasmon-induced ET in assemblies containing colloidal Cu QD and molecular acceptors and study the photodynamics of Cu QD directly grown on metal oxide films. The effect of pump photon energy on the transfer mechanism in metal QD/TiO2 (QD as electron donor or acceptor) will be explored.We plan to extend our research on QD-based energy transfer systems and want to include the process of two-photon absorption. In an ideal case a large band gap QD (ZnSe) will act as two-photon absorber and subsequently transfer the excitation energy to trigger a certain functionality. This process could e.g. boost the two-photon cross-section of established phototriggers.

在过去的几十年里，低成本太阳能电池作为广泛使用的硅基光伏（PV）设备的替代品引起了人们的极大兴趣。在该领域，以分子染料作为光吸收剂的染料敏化太阳能电池（DSSC）的转换效率达到11.9%，电子转移（ET）时间达到飞秒时间尺度。受 DSSC 的启发，开发了量子点太阳能电池 (QDSC)，其中通过半导体量子点 (QD) 实现光收集。量子点表现出抗光降解的鲁棒性、低至近红外的大消光系数以及载流子倍增机制。 QDSC 提高转换效率的主要障碍是由于 QD 的表面积与体积比较大而充当电荷陷阱的子带隙态和非辐射表面复合过程。半导体 QD 的替代方案是金属 QD（Au、Ag、Cu），可通过等离激元诱导 ET 转化为 TiO2。之前的项目旨在研究 QD 分子受体组件中的电荷和能量转移过程，重点关注电荷分离异质结构和热电荷载流子。此外，还成功地研究了染料/半导体界面处的光诱导 ET 和相干现象。根据第一个资助期，我们将研究电荷分离异质结构，并重点关注多激子的分离，特别强调壳层效应。此外，空穴（核）和电子（壳）的量子点本征电荷分离动力学将通过间距大的带隙壳间（洋葱状量子点）来操纵。通过改变壳间厚度，应该改变核和壳之间的电子耦合，从而导致不同的电荷分离动力学。我们已经实施了近红外瞬态吸收装置，成功合成了对光伏应用特别感兴趣的胶体 PbS QD，并开始了光谱表征。我们将测试包含 PbS QD 和分子电子受体的系统的 ET 动力学，并快速转向直接在金属氧化物薄膜表面生长的 PbS QD 的研究。为了避免标准半导体量子点的有毒元素，金属量子点可以作为替代品。我们将研究含有胶体 Cu QD 和分子受体的组件中的表面等离子体诱导的 ET，并研究直接生长在金属氧化物薄膜上的 Cu QD 的光动力学。将探讨泵浦光子能量对金属 QD/TiO2（QD 作为电子供体或受体）传输机制的影响。我们计划扩展对基于 QD 的能量传输系统的研究，并希望包括双光子吸收过程。在理想情况下，大带隙量子点（ZnSe）将充当双光子吸收器，并随后转移激发能量以触发特定功能。这个过程可以例如提高已建立的光触发器的双光子横截面。