Mahapatra Apurba, Runjhun Rashmi, Nawrocki Jan, Lewiński Janusz, Kalam Abul, Kumar Pawan, Trivedi Suverna, Tavakoli Mohammad Mahdi, Prochowicz Daniel, Yadav Pankaj
Department of Physics & Astronomy, National Institute of Technology, Rourkela, 769008, India.
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
Phys Chem Chem Phys. 2020 May 28;22(20):11467-11473. doi: 10.1039/d0cp01119c. Epub 2020 May 11.
Ion migration plays a significant role in the overall stability and power conversion efficiency of perovskite solar cells (PSCs). This process was found to be influenced by the compositional engineering of the A-site cation in the perovskite crystal structure. However, the effect of partial A-site cation substitution in a methylammonium lead iodide (MAPbI) perovskite on the ion migration process and its activation energy is not fully understood. Here we study the effect of a guanidinium (GUA) cation on the ion transport dynamics in the single crystalline GUAMAPbI perovskite composition using temperature-dependent electrochemical impedance spectroscopy (EIS). We find that the small substitution of MA with GUA decreases the activation energy for iodide ion migration in comparison to pristine MAPbI. The presence of a large GUA cation in the 3D perovskite structure induces lattice enlargement, which perturbs the atomic interactions within the perovskite lattice. Consequently, the GUAMAPbI crystal exhibits a higher degree of hysteresis during current-voltage (J-V) measurements than the single-crystalline MAPbI counterpart. Our results provide the fundamental understanding of hysteresis, which is commonly observed in GUA-based PSCs and a general protocol for in-depth electrical characterization of perovskite single crystals.
离子迁移在钙钛矿太阳能电池（PSC）的整体稳定性和功率转换效率中起着重要作用。人们发现这一过程受钙钛矿晶体结构中A位阳离子的组成工程影响。然而，甲基碘化铅（MAPbI）钙钛矿中部分A位阳离子取代对离子迁移过程及其活化能的影响尚未完全了解。在此，我们使用温度相关的电化学阻抗谱（EIS）研究胍基（GUA）阳离子对单晶GUAMAPbI钙钛矿组成中离子传输动力学的影响。我们发现，与原始MAPbI相比，用GUA对MA进行少量取代会降低碘离子迁移的活化能。3D钙钛矿结构中存在大的GUA阳离子会导致晶格增大，从而扰乱钙钛矿晶格内的原子相互作用。因此，与单晶MAPbI相比，GUAMAPbI晶体在电流-电压（J-V）测量过程中表现出更高程度的滞后现象。我们的结果提供了对滞后现象的基本理解，滞后现象在基于GUA的PSC中普遍存在，并且为钙钛矿单晶的深入电学表征提供了通用方案。
