The chemistry and device physics of organic solar cells based on non-fullerene acceptors

基于非富勒烯受体的有机太阳能电池的化学和器件物理

• 批准号: 2910282
• 金额: --
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2910282
• 关键词: chemistry; device; physics; organic; solar

"This project falls within the EPSRC Solar technology, Optoelectronic Devices and Circuits, and Materials for Energy Applications research areas. Organic solar cells (OSCs) have the potential to be next-generation renewable energy harvesters due to their lightweight, solution processability, flexibility and semi-transparency. Recent inventions of record high performance non-fullerene fused ring electron acceptors (FREAs) have increased power conversion efficiencies (PCEs) to over 19% in a single cell device. Conventionally in organic photovoltaics (OPV), excitons (bound electrons and holes) are intrinsically photogenerated due to the photoactive layer having a low dielectric constant causing excitons with high binding energies and therefore leading to poorer device performance. Thus, separating excitons into free charge carriers requires a heterojunction between donor and acceptor molecules. However, this heterojunction has been reported to cause instabilities at the interface and limits the PCE, therefore this work will solely focus on single-component homojunction OSCs. The FREAs that will be investigated throughout the PhD project is Y6, COTIC-4F and COTIC-4Cl. The Y6 molecule is among the common FREAs that has demonstrated an acceleration in PCE. It has an acceptor-donor-acceptor (A-D-A) structure consisting of a core, two electron accepting terminal moieties and solubilising alkyl substituents. Y6 has proven to intrinsically generate free charge carriers (rather than excitons) without a heterojunction giving hope to the possibility of efficient homojunction devices. COTIC-4F/4Cl are novel narrow bandgap non-fullerene acceptors containing an A-D-D-D-A structure that can enhance intramolecular charge transfer and also lower the optical bandgap to 1.10 eV. As 50% of solar radiation intensity lies in the near infrared region, possessing a low optical bandgap is therefore desirable to harvest solar radiation. As of yet, it has not been reported whether these narrow bandgap acceptors can also intrinsically generate free charge carriers in neat films. Thus, this work will research the charge dynamics in neat films and if successful single component homojunction devices will be fabricated. Another active area of research will be the introduction of dopants to the COTIC-4F/4Cl photoactive layer to improve the charge transport properties of OSCs. Along with a significant number of free charge carriers generated by the doping process, device performance-enhancing morphological impacts such as optimised crystallinity and reduced trap density can occur concurrently. By simultaneously performing both p and n-type doping to the active layer, the aim is to form a p-i-n junction that will enable an efficient transport of charge carriers towards the metal contacts. FREAs have permitted the current growth in PCE, but only for solution-processed systems. Vacuum processed OSCs were found to have a higher morphological stability than solution processed OSCs which could be due to susceptibility of side chain degradation, and molecules finding near equilibrium structures during film growth. The key advantages of vacuum coating processes are that they are inexpensive and fast to coat large surface areas. Coupling this with minimal material consumption, low temperature processing and compatibility with flexible substrates, this could potentially make OSCs the cheapest source of electricity in the world. Y6 is too large to be vacuum processed thus, by synthetically removing the bulky alkyl side chains should make it small enough to be vacuum processed."

“该项目属于 EPSRC 太阳能技术、光电器件和电路以及能源应用材料研究领域。有机太阳能电池 (OSC) 由于其轻质、溶液可加工性、灵活性和最近发明的创纪录的高性能非富勒烯稠环电子受体 (FREA) 将单电池器件的功率转换效率 (PCE) 提高到了 19% 以上。在光伏器件（OPV）中，激子（束缚电子和空穴）本质上是光生的，因为光敏层具有低介电常数，导致激子具有高结合能，因此导致器件性能较差，因此，将激子分离成自由电荷载流子需要异质结。然而，据报道，这种异质结会导致界面不稳定并限制 PCE，因此这项工作将仅关注单组分同质结 OSC。将在整个博士项目中研究的 FREA 是 Y6、COTIC-4F 和 COTIC-4Cl。 Y6 分子是常见的 FREA 分子之一，已证明 PCE 加速。它具有受体-供体-受体（A-D-A）结构，由一个核心、两个电子接受末端部分和增溶烷基取代基组成。事实证明，Y6 无需异质结即可本质上产生自由载流子（而不是激子），这为高效同质结器件的可能性带来了希望。 COTIC-4F/4Cl是新型窄带隙非富勒烯受体，含有A-D-D-D-A结构，可以增强分子内电荷转移并将光学带隙降低至1.10 eV。由于 50% 的太阳辐射强度位于近红外区域，因此需要具有较低的光学带隙来收集太阳辐射。迄今为止，尚未报道这些窄带隙受体是否也能在纯薄膜中本质上产生自由载流子。因此，这项工作将研究纯薄膜中的电荷动力学，以及是否能够成功制造单组件同质结器件。另一个活跃的研究领域是将掺杂剂引入 COTIC-4F/4Cl 光活性层，以改善 OSC 的电荷传输性能。随着掺杂过程产生大量自由载流子，器件性能增强的形态影响（例如优化的结晶度和降低的陷阱密度）可以同时发生。通过同时对有源层进行 p 型和 n 型掺杂，目的是形成 p-i-n 结，从而实现电荷载流子向金属触点的有效传输。 FREA 允许当前 PCE 的增长，但仅限于解决方案处理的系统。研究发现，真空处理的 OSC 比溶液处理的 OSC 具有更高的形态稳定性，这可能是由于侧链降解的敏感性以及薄膜生长过程中分子发现接近平衡结构的缘故。真空镀膜工艺的主要优点是价格便宜且可以快速涂覆大面积的镀膜。再加上最少的材料消耗、低温处理以及与柔性基板的兼容性，这可能使 OSC 成为世界上最便宜的电力来源。 Y6 太大而无法进行真空处理，因此，通过合成去除大的烷基侧链应该使其小到足以进行真空处理。”