Lattice Dynamics of MAPbI3 Nanocrystals
Andrea Rubino a, Mauricio Calvo a, Hernan Miguez a, Alejandro Goñi b
a Instituto de Ciencia de Materiales de Sevilla (ICMS-CSIC), C/ Américo Vespucio 49, Seville, 41092, Spain
b Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Spain
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics and Perovskite Photonics and Optoelectronics (NIPHO20)
Sevilla, Spain, 2020 February 23rd - 25th
Organizer: Hernán Míguez
Poster, Andrea Rubino, 014
Publication date: 25th November 2019

Optoelectronic devices based on the use of APbX3-type perovskites have demonstrated the enormous potential offered by such semiconductors especially in the photovoltaic field. Parallel to the impressive technological results, there are nevertheless open debates on the origins of their fundamental properties. The study of the correlation between the dynamics of the crystalline network and the electronic properties is a clear example [1]. The polar nature of these so-called “soft” materials can play an important role on the response to vibrational movements that can influence, for example, the mobility of the generated charges. In the case of the MAPbI3 bulk material, it is well known how the bandgap presents an unusual temperature dependence with respect to the general trend for inorganic semiconductors [2]. In this regard it has been recently demonstrated how the thermal expansion and the electron-phonon coupling contribute equally to the variation of the bandgap with the temperature [3]. Together with perovskite solar cells research boom, the nanocrystal counterparts also proved to be an interesting alternative for light emission (high quantum yield) and tandem solar cells applications (bandgap tunability) [4]. Even so, the study of their optoelectronic features suffers from lack of data, partly due to the difficulty in obtaining homogeneous materials suitable for the techniques for the optical characterization. In this work we have been able to carry out an in-depth analysis of the dependence of the bandgap of MAPbI3 nanocrystals with temperature, being able to discriminate the contribution of thermal expansion and electron-phonon interactions making use of photoluminescence measurements at low temperature and high pressure. This type of characterization is possible thanks to the use of an alternative method for the preparation of nanocrystals, in which the perovskites are embedded into a porous SiO2-based matrix in the form of a thin film with optical quality [5]. This allows to monitor the behavior of perovskites in a direct way, using a neutral dielectric environment and avoiding the distortions, in the response, generated by the presence of ligands.

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