Fluorination of Organic Spacer Impacts on the Structural and Optical Response of 2D Perovskites

Frontiers in Chemistry

Gianluca Pozzi¹  Marco Cavazzini¹  Simonetta Orlandi¹  Giulia Grancini²  Inés García-Benito³  Mohammad Khaja Nazeeruddin³  Valentin I. E. Queloz³  Dieter Neher⁴  Yana Vaynzof⁵  David Becker-Koch⁵  Yvonne J. Hofstetter⁵  Claudio Quarti⁷  Jacky Even⁸  Pietro Caprioglio⁹ 

[1] CNR - Istituto di Scienze e Tecnologie Chimiche “G. Natta” (CNR-SCITEC), Milan, Italy;Dipartimento di Chimica Fisica, University of Pavia, Pavia, Italy;Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, EPFL Valais Wallis, Sion, Switzerland;Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany;Integrated Centre for Applied Physics and Photonic Materials and Centre for Advancing Electronics Dresden (CFAED), Technical University of Dresden, Dresden, Germany;Laboratory for Chemistry of Novel Materials, Department of Chemistry, Université de Mons, Mons, Belgium;Univ Rennes, ENSCR, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR 6226, Rennes, France;Univ Rennes, INSA Rennes, CNRS, Institut FOTON - UMR 6082, Rennes, France;Young Investigator Group Perovskite Tandem Solar Cells, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Germany;

关键词: fluorinated organic spacer;    2D perovskites;    phase transition;    temperature dependence;    excitonic materials;   

DOI  :  10.3389/fchem.2019.00946

来源: DOAJ

【 摘 要 】

Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)2PbI4 and (Lf)2PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.

【 授权许可】

Unknown