Physics at Virginia

Two-dimensional hybrid organic-inorganic perovskites (HOIPs) have shown promising progress in light-emitting diodes applications. The three-dimensional (3D) HOIPs, commonly used as novel solar cells, exhibit extended charge carrier lifetimes, long carrier diffusion lengths, and exceptional carrier protection from defects [1]. It has been experimentally shown that the reorientation of the polarized organic molecules can facilitate the polaron formation, where polaron is referred as a quasiparticle formed by the Coulomb interaction between an excess charge (an electron or a hole) and the ionic lattice, enhance the screening effects on charge carriers, and thus prolong the charge carrier lifetime [2-3]. Whereas the pure inorganic 3D perovskites without organic molecules, such as CsPbI3, also show a moderate photovoltaic performance, which brings researcher’s efforts into investigations on dynamics of the inorganic perovskite framework [4]. An understanding of the microscopical mechanisms behind extended charge carrier lifetimes, long carrier diffusion lengths, and exceptional carrier protection in HOIPs is lacking. We performed time-of-flight neutron spectroscopy for two perovskites, butylammonium lead iodide (BA)2PbI4 (BA) and phenethyl-ammonium lead iodide (PEA)2PbI4 (PEA). From the obtained spectra we identified and quantitatively separated the rotational and phonon contribution for BA. Similar analysis would be performed for the PEA spectra in future. We try to understand how both inorganic vibrational dynamics and organic molecule rotational dynamics contribute to charge carrier lifetime and hence power conversion efficiency of solar cells. The study is important to get an idea on how to engineer new HOIPs by exploiting these dynamics for higher device performance. By examining the corresponding temperature dependence, we revealed that the rotational dynamics of organic molecules in these materials tends to suppress their photoluminescence quantum yield [5] while the vibrational dynamics did not show predominant correlations with their optoelectronic properties.


[1] Mei, Anyi, et al. science 345.6194 (2014): 295-298.

[2] Miyata, Kiyoshi, Timothy L. Atallah, and X-Y. Zhu. Science Advances 3.10 (2017): e1701469.

[3] Chen, Tianran, et al. Proceedings of the National Academy of Sciences 114.29 (2017): 7519-  7524.

[4] Wang, Kang, et al. Nature communications 9.1 (2018): 4544.

[5] Gong, Xiwen, et al. Nature materials 17.6 (2018): 550-556.


Condensed Matter Seminar
Wednesday, April 12, 2023
3:00 PM
Physics, Room 120
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