Pushing the FF of Non-Fullerene Acceptors Based Solar Cells Above 80%: Relating Order to Reduced Recombination to Device Performance

有机体异质结太阳能电池的最新进展，特别是非富勒烯受体(NFA)的最新发展，导致了功率转换效率的大幅提高，目前领先的单结器件的认证效率为17.6%。作为一个重要的光伏参数，OSCs的填充因子(Ff)代表了自由电荷的产生和提取在竞争成倍和非成倍损耗时的电场依赖关系。然而，这种高效率电池的FF值仍然远远低于Shockley-Queisser极限。因此，本项目的超常目标是通过研究和了解光活化层中施主和受主的结晶度和可混性在决定JV特性的过程中所起的特殊作用，推动高效有机太阳能电池的发展。因此，我们将重点研究自由光生载流子的输运和复合与多组分共混层的结构和能量性质的关系。为此，我们将利用波茨坦大学建立的各种技术，如T依赖的空间电荷限制电流、阻性光电压、时延采集场和光诱导吸收来得出电荷载流子动力学的最终图景。这些研究将在一系列基于Y型非饱和脂肪酸的混合物上进行，Y-型非饱和脂肪酸因其特殊的化学和结构特征而被选择。这些实验研究的结果将作为数值模拟的输入，以确认本体和表面复合的作用，以及它们如何主要确定FF和VOC。通过这样做，我们的目标是确定需要满足的标准，以实现同时有效的电荷提取和高度抑制的(非朗之万文)复合，并可靠地推动这些器件的FF超过80%。

Recent advances in organic bulk heterojunction solar cells, enabled in particular by the recent development of non-fullerene acceptors (NFAs), have led to large improvements in the power conversion efficiency, with current leading certified efficiencies of 17.6% for single-junction devices. As an important photovoltaic parameter, the fill factor (FF) of OSCs stands for the electric field dependence of free charge generation and extraction in competition to geminate and non-geminate losses. However, the FF values of such high efficiency cells still lie well below the Shockley-Queisser limit. Therefore, the overreaching goal of this project is to push the FF of highly-efficient organic solar cells by investigating and understanding the particular roles that crystallinity and miscibility of the donor and the acceptor in the photoactive layer have on the processes determining the JV-characteristics. Hereby, we will focus on the detailed investigation of the transport and recombination of free photogenerated carriers in relation to structural and energetic properties of the multicomponent blend layer. To this end, we will employ various techniques established at Potsdam University such as T-dependent space charge limited currents, resistive photovoltage, time-delayed collection field and photoinduced absorption to arrive at a conclusive picture of the charge carrier dynamics. These studies will be performed on a series of blends based on Y-type NFAs, which are chosen for their particular chemical and structural characteristics. Results from these experimental investigations will serve as input to numerical simulations to confirm the role of bulk and surface recombination and how they determine primarily the FF but also the VOC. By doing so, we aim at identifying the criteria which needs to be met to realize, simultaneously, efficient charge extraction and highly suppressed (non-Langevin) recombination, and to push the FF of these devices reliably above 80%.