Improving intrinsic stability of perovskite solar cells by additives

为了找出如何提高卤化铅钙钛矿太阳能电池的稳定性，我们的跨学科团队研究了EPFL在SPP 2196的第一个资助期内开发的几种稳定添加剂。我们研究了它们对Cs0.05MA0.05FA0.90PbI3吸收剂太阳能电池的影响，在热应力下，功率转换效率高于21%，同时控制薄膜的形貌，晶体学性质，光学性质，电荷载流子迁移率和开路电压。迄今为止获得的结果清楚地表明，用官能化添加剂制备的膜和器件的稳定性得到改善，特别是在不损害性能效率的情况下。此外，我们已经取得了一些进一步有趣的观察方面的离子迁移和光致发光猝灭效率，并发现了强烈的影响，所有这些效果的中孔电子传输层。因此，我们提出了一个有针对性的研究项目，以明确地阐明相互作用机制和预选离子液体的作用的起源以及它们背后的微观机制，同时也证明它们对其他钙钛矿组合物的适用性。在实验方面，我们将采用两种瞬态技术来研究，一方面，相对较快的过程中的自由载流子复合使用微波为基础的TRMC方法，另一方面相对较慢的过程中的离子迁移使用瞬态开路电压（MOCVD）。该研究项目的成果将是理解离子液体与钙钛矿本体以及界面之间的相互作用机制，并最终发展概念，以提高钙钛矿太阳能电池的固有稳定性。特别注意的是在设备操作过程中的离子迁移，这有助于钙钛矿层的不稳定。目前，尚不清楚哪种确切机制导致这种离子迁移以及如何使其最小化，例如避免与金属氧化物或其他内部界面的可能反应，而且确保太阳能电池内的限定电场分布，使得可以可靠地描述和预测其电行为。最后但并非最不重要的是，当使用也是离子的稳定添加剂时，区分钙钛矿吸收剂中的本征和非本征离子也非常重要，这在实验上迄今为止还不可能。

Aiming to find out how to improve the stability of lead halide perovskite solar cells, our interdisciplinary team investigated several stabilising additives developed at EPFL during the first funding period of SPP2196. We studied their effect on solar cells with Cs0.05MA0.05FA0.90PbI3 absorbers with power conversion efficiency higher than 21% under thermal stress, while controlling the film morphology, crystallographic properties, optical properties, charge carrier mobility and open circuit voltage. The results obtained so far clearly indicate an improved stability of the films and devices prepared with functionalised additives, especially without compromising the performance efficiency. In addition, we have made some further interesting observations with regard to ion migration and photoluminescence quenching efficiency and found a strong influence of the mesoporous electron transport layer on all these effects. We therefore propose a targeted research project to definitively clarify the interaction mechanisms and the origin of the effect of pre-selected ionic liquids as well as the microscopic mechanism behind them, but also to prove their applicability to other perovskite compositions. On the experimental side, we will apply two transient techniques to study, on the one hand, relatively fast processes of free carrier recombination using the microwave-based TRMC method and on the other hand relatively slow processes related to ion migration using transient open circuit voltage (OCVD). The outcome of the research project will be the understanding of the mechanisms of interaction between ionic liquids and perovskite bulk as well as interfaces, and finally the development of concepts to improve the intrinsic stability of perovskite solar cells in general. Particular attention is paid to ion migration during device operation, which contributes to destabilisation of the perovskite layer. At present, it is not clear which exact mechanisms lead to this ion migration and how it can be minimised, e.g. to avoid possible reactions with the metal oxide or other internal interfaces, but also to ensure a defined electric field distribution within the solar cell so that ist electrical behaviour can be reliably described and predicted. Last but not least, when using stabilising additives, which are also ions, it is also very important to distinguish between intrinsic and extrinsic ions in the perovskite absorber, which has not been possible experimentally so far.