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."

该项目福尔斯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）由于其重量轻，溶液可加工性，灵活性和半透明性，有可能成为下一代可再生能源收割机。最近发明的创纪录的高性能非富勒烯稠环电子受体（FREA）在单电池器件中将功率转换效率（PCE）提高到19%以上。常规地，在有机光致发光（OPV）中，激子（束缚电子和空穴）由于具有低介电常数的光活性层而固有地光生，从而产生具有高结合能的激子，并因此导致较差的器件性能。因此，将激子分离成自由电荷载流子需要供体和受体分子之间的异质结。然而，据报道，这种异质结会导致界面处的不稳定性并限制PCE，因此本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Y 6，COTIC-4F和COTIC-4Cl。Y 6分子是已证明PCE加速的常见FREA之一。它具有受体-供体-受体（A-D-A）结构，其由核、两个电子接受末端部分和增溶烷基取代基组成。Y 6已经被证明在没有异质结的情况下固有地产生自由电荷载流子（而不是激子），这给高效同质结器件的可能性带来了希望。COTIC-4F/4Cl是一种新型的窄带隙非富勒烯受体，具有A-D-D-D-A结构，可以增强分子内电荷转移，并将光学带隙降低到1.10 eV。由于50%的太阳辐射强度位于近红外区域，因此期望具有低光学带隙以收获太阳辐射。到目前为止，还没有报道这些窄带隙受体是否也可以在纯净的薄膜中本质上产生自由电荷载流子。因此，这项工作将研究在净膜的电荷动力学，如果成功的单组分同质结器件将被制造。另一个活跃的研究领域将是向COTIC-4F/4Cl光活性层引入掺杂剂，以改善OSC的电荷传输特性。沿着由掺杂工艺产生的大量自由电荷载流子，可以同时发生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。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，该p-i-n结将使得电荷载流子能够朝向金属接触有效传输。FREAs允许PCE的当前增长，但仅限于溶液处理系统。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，以及在膜生长期间分子发现接近平衡的结构。真空镀膜工艺的主要优点是成本低廉，且可快速涂覆大表面积。再加上最小的材料消耗，低温处理和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。Y 6太大而不能进行真空处理，因此，通过合成除去大体积烷基侧链应使其足够小以进行真空处理。"