Lifetime and encapsulation study of organic solar cells (LEOsc)

《巴黎协定》设定了到2050年实现净零排放的目标，以应对全球变暖；这激发了对能源转换的大量研究。光伏技术由于能够在不排放温室气体的情况下将太阳辐射转化为电能，满足日益增长的能源需求而备受关注。然而，全球光伏部署仍然很低（2021年全球只有5%的电力来自光伏技术），市场目前由能源密集型传统晶体硅光伏主导。为了促进能源转型，新型光伏技术，如有机太阳能电池（OSCs），正在深入研究柔性和轻量化应用。然而，osc必须在效率、寿命和成本方面满足未来商业化的要求。与传统硅相比，OSC的生产和安装成本预计将非常低。在提高OSC效率方面取得了持续的发展，到目前为止已经达到了大约20%的具有竞争力的高PCE（功率转换效率）。而OSC寿命仍明显低于无机电池，还有很大的改进空间。由于盐含量的降解主要是由暴露于水分和氧气引起的，因此将电池封装是提高盐含量预期寿命的最直接方法之一。在此背景下，本奖学金的研究重点是OSC终身研究。提出的任务包括两个方面：封装层开发和盐盐外在降解机制研究。具体地说，原子层沉积（ALD）技术将被用于封装层的制造。ALD是一种基于不同前驱体之间的自限制反应的技术，可以沉积致密均匀的薄膜。膜的均匀性使得水和氧的渗透率极低，因此封装膜可以更长时间地保护osc。该奖学金将系统地研究ALD技术的所有封装策略，即：(1)层压的屏障膜。这种策略允许提前制造屏障膜的可能性，然后osc将与屏障膜层压。该方案的一个巨大优势是模块的整个处理可以在卷对卷配置中完成，并且ALD条件不受敏感有机物的限制。(2)直接薄膜封装（TFE）。这种策略是理想的，以尽量减少机械应力，磨损的屏障，和设备污染。TFE的主要问题是包封处理条件受有机物的高度限制。在这两种策略中，都将开发具有低透湿性和足够机械耐久性的OSC封装层，并开发中间层作为ALD材料更好的生长表面，以确保薄膜的完美性。提高沉积速率，提高ALD的生产能力。通过比较不同策略中的封装性能，可以找到osc的最佳封装配置。此后，将采用最佳封装来保护最先进的OSCs，并对受保护的OSCs进行加速试验和室外寿命试验，以表征其寿命。包被细胞的外部降解也将被研究，以解决细胞分解。根据退化机制对封装层给出优化策略。我的目标是推动OSC的寿命达到与Si相当的水平。在奖学金结束时，将在牛津物理学院创新与企业经理（Phillip Tait）和我们的行业合作伙伴的帮助下进行规模试验。

The Paris Agreement set the goal to reach Net-Zero emission by 2050 to tackle global warming; this has stimulated much research into energy transition. Photovoltaic technology receives great attention as it can meet increasing energy demands by converting solar radiation into electricity without greenhouse gas emissions. However, global PV deployment is still low (only 5% of global electricity came from PV technology in 2021) and the market is currently dominated by energy-intensive conventional crystalline silicon PV. To facilitate the energy transition, novel photovoltaic technologies, such as organic solar cells (OSCs), are being intensively studied for flexible & lightweight applications. However, OSCs must fulfil requirements in efficiency, lifetime, and cost for future commercialisation. The cost of OSC production and installation is expected to be very low compared to conventional Si. Continuing developments have been made in improving OSC efficiency and indeed competitive high PCE (power conversion efficiency) of about 20% has been reached so far. While OSC lifetime is still substantially lower than that of inorganic cells and there is much room for improvement. Since OSC degradation is mainly caused by exposure to moisture and oxygen, encapsulation of the cells is one of the most straightforward ways to improve OSC life expectancy. In this context, this Fellowship research focusses on the OSC lifetime study. The proposed tasks involve two aspects, encapsulation layer development and OSC extrinsic degradation mechanism study.Specifically, the atomic layer deposition (ALD) technique will be utilized for the fabrication of the encapsulation layer. ALD is a technique based on the self-limiting reaction between distinct precursors, which can deposit dense thin films with excellent uniformity. The uniformity of the film allows the water and oxygen permeation rate to be extremely low, thus the encapsulation film can protect OSCs longer. The Fellowship will systematically investigate all the encapsulation strategies by the ALD technique, namely: (1) Barrier films for lamination. This strategy allows the possibility of manufacturing the barrier films in advance, then OSCs will be laminated with barrier films. A huge advantage of this scheme is the whole processing of a module can be done in a roll-to-roll configuration and the ALD conditions are not limited by the sensitive organics. (2) Direct thin-film encapsulation (TFE). This strategy is desirable to minimize mechanical stress, abrasion to the barrier, and device contamination. The main issue of TFE is the encapsulation processing conditions are highly constrained by the organics. In both strategies, OSC encapsulation layers with low moisture permeation and sufficient mechanical durability will be developed, an intermediate layer will also be developed to serve as a better growth surface for ALD materials to ensure the thin films are perfect. The deposition rate will be improved to increase the production throughput of ALD. Comparisons of the encapsulation performance within the different strategies will address the best encapsulation configuration for OSCs. Thereafter, the optimal encapsulation will be utilised for the protection of state-of-the-art OSCs, accelerated tests and outdoor lifetime tests will be performed on the protected OSCs to characterise the lifetime. The extrinsic degradation of encapsulated cells will be also studied to address the cell break-down. Optimisation strategies will be given to the encapsulation layers according to the degradation mechanism. My goal is to push the lifetime of the OSC to a comparable level to that of Si. At the end of the Fellowship, scale-up trials will be undertaken with the help of Oxford Physics' Innovation and Enterprise Manager (Phillip Tait) and our industry partners.