Understanding the role of organic ligands on charge transport and photocurrent generation in layered perovskites

卤化物钙钛矿在太阳能应用方面显示出巨大的潜力，因为钙钛矿太阳能电池现在在单结设备上的效率高达25.7%不幸的是，钙钛矿太阳能电池的发展受到其对湿气、氧气、光照、热应力和偏置应力的强烈敏感性的阻碍仅靠封装技术的进步不足以让钙钛矿太阳能电池进入市场。因此，解决稳定问题至关重要。为了保护卤化物钙钛矿薄膜不受水分的影响，这是钙钛矿基器件降解的关键触发因素，在晶格中引入了更大的疏水有机阳离子（配体）因此，晶体相被修改为形成二维或层状钙钛矿结构，其中无机八面体板被配体分开。虽然这种改进提供了更高的环境稳定性，但它的性能代价是太阳能电池效率的急剧下降，部分原因是电荷传输和激子解离的显著破坏。针对这一挑战，目前正在探索两个研究方向：1)创建混合3D-2D钙钛矿结构，在稳定性和效率之间找到合理的平衡；2)找到合适的配体来限制其对效率的负面影响在这个项目中，我们将重点关注第二个方面，并将致力于提高我们对配体对层状钙钛矿中电荷传输和激子离解的影响的理解。特别是，我们将调整有机配体的长度，并跟踪其对半导体薄膜的各种输运和光电子性质的影响。我们还将通过比较Ruddlesden-Popper相与Dion-Jacobson相的性质，探讨有机配体之间的范德华间隙对Ruddlesden-Popper相的影响。本研究的目的是通过实验确定最大配体大小，以确保无机板之间的充分耦合。此外，我们将确定Dion-Jacobson相是否应该优先于Ruddlesden-Popper相，后者是目前2D-3D钙钛矿太阳能电池研究的主要焦点国家可再生能源实验室。最佳研究——电池效率图表，2021年。[10]李建军，李建军，李建军，等。应用化学学报，2017,9(2):992 - 992。[10]梁廷亮，等。Mater. 2022, 3, 1。[10]刘建军，王志强，等，中国生物医学工程学报，2017,26(3):1224 - 1224。[10]刘建军，刘建军，刘建军，等。能源工程学报，2002,22(2):448 - 448。[10]傅焕华，马特。化学。[C] 2017,9, 6378.]

Halide perovskites show great potential for solar energy applications as perovskite solar cells now achieve efficiencies as high as 25.7% for single junction devices.[1] Unfortunately, the rise of perovskite solar cells is hindered by their strong sensitivity to moisture, oxygen, illumination, thermal and bias stresses.[2] Progress in encapsulation technologies alone will not suffice to allow market entry of perovskite solar cells. It is therefore crucial to tackle the question of stability.In order to protect halide perovskite films from moisture, a key trigger of degradation in perovskite-based devices, larger and hydrophobic organic cations (ligands) have been introduced in the crystal lattice.[3] As a consequence, the crystal phase is modified to form a 2D- or layered perovskite structure with slabs of inorganic octahedra separated by ligands. While this modification offers higher environmental stability, it comes at the cost of performance with a drastic loss in solar cell efficiency, in part due to a significant disruption of charge transport and exciton dissociation.[4]In view of this challenge, two research directions are currently being explored: 1) creating a mixed 3D-2D perovskite structure to find a reasonable balance between stability and efficiency;[5] and 2) finding the appropriate ligand to limit its negative impact on efficiency.[6] In this project we will focus on the second aspect and will aim at improving our understanding of the impact of ligands on charge transport and exciton dissociation in layered perovskites. In particular, we will tune the length of the organic ligand and follow its impact on various transport and optoelectronic properties of the semiconducting film. We will also explore the influence of the Van der Waals gap between organic ligands present in the Ruddlesden-Popper phase by comparing its properties with the Dion-Jacobson phase. The goal of this study will be to determine experimentally a maximum ligand size to ensure sufficient coupling between inorganic slabs. In addition, we will ascertain whether the Dion-Jacobson phase should be preferred to the Ruddlesden-Popper one, which is currently the main focus of research efforts in 2D-3D perovskite solar cells.[1] NREL, National Renewable Energy Laboratory. Best Research-Cell Efficiency Chart, 2021. [2] L. Schmidt-mende, et al., APL Mater. 2021, 9, 109202. [3] T. L. Leung, et al., Commun. Mater. 2022, 3, 1. [4] M. S. Holanda, et al., EcoMat 2021, 3, e12124. [5] A. Caiazzo, R. A. J. Janssen, Adv. Energy Mater. 2022, 2202830. [6] H. Fu, J. Mater. Chem. C 2021, 9, 6378.