Nano-scale Chemical Imaging of Vapor processed (PEA)2(MA)n-1PbnI3n+1 Quasi-2D perovskite Solar Cells

Hung Wei Shiu^1*, Ming-Hsien Li², Li-Chung Yu¹, Yu-Ling Lai¹, Takuji Ohigashi³, Nobuhiro Kosugi³, Peter Chen², Yao-Jane Hsu¹

¹Nano Science group, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
²Department of Photonics, National Cheng Kung University, Tainan, Taiwan
³UVSOR Synchrotron, Institute for Molecular Science, Okazaki, Japan

* Presenter:Hung Wei Shiu, email:hwshiu@nsrrc.org.tw

In the last couple years, a dimensionally tuned quasi-2D perovskite thin film was developed which is systematically synthesized by introducing a large organic cation, phenylethylammonium (PEA = C8H9NH3) at a judiciously-chosen stoichiometry. The quasi-2D perovskite exhibits the capability of combination of enhanced stability of 2D perovskite and outstanding optoelectronic properties of 3D perovskite. In our previous studies, we have successfully synthesized dimensional tunable quasi-2D perovskite by mixing stoichiometric quantities of lead iodide (PbI2), MAI (Ch3NH3I) and PEAI to yield compounds with different layer numbers of n in the series of (PEA)2(MA)n-1PbnI3n+1. By using MAI vapor-assisted method can achieve control of the morphology, compact and highly stable crystalline layer. The PCEs up to 19.1% and 18.69% were achieved with n = 40 and n =60, respectively and both of them showed higher performance than the standard 3D perovskite of MAPbI3 (PCEs = 17.31%, n = ∞) and 2D perovskite of (PEA)2MAPb2I7 (PCEs < 15%). Besides, compare with the SEM results, it implied that the change of the morphology due to the amount of large organic cation, PEAI may play an important role for the photovoltaic performance. In this work, we will systematically discuss about the layer number dependent behavior of (PEA)2(MA)n-1PbnI3n+1 Quasi-2D perovskite by X-ray photoelectron spectroscopy (XPS), Near-edge X-ray absorption fine structure (NEXAFS), and scanning transmission X-ray microscopy (STXM).

Keywords: STXM, Solar Cell, Perovskite, NEXAFS