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、光电子器件和电路以及能源应用材料的研究领域。有机太阳能电池(OSC)具有重量轻、溶液可加工性、灵活性和半透明性等特点，有望成为下一代可再生能源收集器。最近发明的创纪录的高性能非富勒烯稠环电子受体(FRIA)将单电池器件的功率转换效率(PCE)提高到19%以上。传统上，在有机光伏(OPV)中，由于光活性层具有低介电常数而导致具有高结合能的激子，从而导致较差的器件性能，因此激子(束缚电子和空穴)本质上是光生产生的。因此，将激子分离成自由载流子需要在供体和受体分子之间建立异质结。然而，这种异质结已被报道在界面处引起不稳定性并限制了PCE，因此本工作将仅集中在单组分同质结OSCs上。在整个PHD项目中将调查的FREAS是Y6、Cotic-4F和Cotic-4CL。Y6分子是表现出PCE加速的常见Freas分子之一。它具有受体-供体-受体(A-D-A)结构，由一个核心、两个接受电子的末端部分和增溶的烷基取代基组成。Y6已经证明，在没有异质结的情况下，本质上可以产生自由电荷载流子(而不是激子)，这为高效的同质结器件带来了希望。CoTiC-4F/4CL是一种新型的窄禁带非富勒烯受体，它具有A-D-A结构，可以增强分子内的电荷转移，并将光学带隙降低到1.10 eV。由于太阳辐射强度的50%位于近红外区域，因此具有较低的光学带隙是获取太阳辐射的理想选择。到目前为止，还没有报道这些窄带隙接受者是否也能在整齐的薄膜中固有地产生自由电荷载流子。因此，这项工作将研究整齐薄膜中的电荷动力学，如果成功，将制造出单组分同质结器件。另一个活跃的研究领域将是在CoTiC-4F/4Cl光活性层中引入掺杂剂，以改善OSCs的电荷传输性能。除了掺杂过程产生的大量自由电荷载流子外，优化结晶度和降低陷阱密度等提高器件性能的形态影响可能会同时发生。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，使载流子能够有效地向金属接触传输。FREAS允许目前PCE的增长，但仅限于溶液处理系统。真空处理的OSCs比溶液处理的OSCs具有更高的形态稳定性，这可能是由于侧链降解的敏感性，以及在薄膜生长过程中找到接近平衡结构的分子所致。真空镀膜工艺的主要优点是，它们价格低廉，可以快速地在大面积表面镀膜。再加上极低的材料消耗、低温加工和与柔性基板的兼容性，这可能会使OSCs成为世界上最便宜的电力来源。Y6太大，不能进行真空加工，因此，通过综合去除笨重的烷基侧链，应该可以使其足够小，可以进行真空加工。