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Can the Spacer Cation Affect the Preferential Growth and Phase Segregation in 2D Ruddelsden-Popper Perovskite?
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Authors
1a School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran
2Center of Excellence in Materials for Low-Energy Consumption Technologies, University of Tehran, Tehran, Iran
3School Of Metallurgy and Materials Eng., College of Eng., University of Tehran
Abstract
Organic-inorganic halide perovskites (OIHP) are an emerging family of semiconductor materials widely used in the fabrication of optoelectric devices, including solar cells, due to their superior optical and electrical properties. Poor long-term stability of OIHPs is the main hindrance to the commercialization of perovskite solar cells. Using 2D Ruddelsden-Popper perovskites with multi-quantum wells (MQWs) structure is a common approach to improving perovskite solar cells' stability. However, the presence of MQWs structure restricts the transport of charges and thus reduces the photovoltaic performance of perovskite solar cells. Out-of-plane growth of 2D perovskite film can significantly improve carrier transport and consequently reduces the rate of non-radiative recombination. One of the main factors that affects the preferential growth of 2D perovskites is the type of spacer cation that exists in the 2D perovskites structure. Herein, butylammonium (BA) and phenetylammonium (PEA) spacer cations, as well as their combination, are employed in 2D perovskite thin film, and their effects on preferential growth and phase segregation have been investigated. X-ray diffraction (XRD) data shows that the preferred peaks of BA-based 2D perovskite have higher intensity and narrower full width at half maximum (FWHM) than the PEA-based counterparts, which is due to the rigid nature of the PEA molecule compared to the BA molecule. It is also observed that the replacement of BA instead of PEA significantly reduces phase segregation. This phenomenon is probably related to the phenyl ring of the PEA molecule, which is entirely solvophobic and slows down the formation of DMF.PEAI complex during the crystallization step, which in turn leads to the formation of small n 2D perovskite nucleus causing phase segregation. SEM images also represent that the BA-based film has a smoother surface and lower pinholes than the PEA-based 2D perovskite.
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