Equal Footing of Thermal Expansion and Electron-Phonon Interaction in the Temperature Dependence of Lead Halide Perovskite Band Gaps

Adrián Francisco-López^a, Bethan Charles^b, Oliver J. Weber^b, M. Isabel Alonso^a, Miquel Garriga^a, Mariano Campoy-Quiles^a, Mark T. Weller^b, Alejandro R. Goñi^a^,^c

^aInstitut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain, Campus UAB, Bellaterra, Spain

^bDept. of Chemistry & Centre for Sustainable Chemical Technologies, University of Bath, UK, Claverton Down, Bath BA2 7AY, Reino Unido, United Kingdom

^cInstitució Catalana de Recerca i Estudis Avançats (ICREA), Spain, Passeig Lluis Companys 23, Barcelona, Spain

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting19 (NFM19)

#PERInt19. Interplay of composition, structure and electronic properties in halide-perovskites

Berlin, Germany, 2019 November 3rd - 8th

Organizer: Pablo P. Boix

Oral, Alejandro R. Goñi, presentation 018
DOI: https://doi.org/10.29363/nanoge.nfm.2019.018
Publication date: 18th July 2019

Lead halide perovskites, which are causing a paradigm shift in photovoltaics, exhibit an atypical temperature dependence of the fundamental gap: it decreases in energy with decreasing temperature. Reports ascribe such a behavior to a strong electron-phonon renormalization of the gap, neglecting contributions from thermal expansion. However, high pressure experiments performed on the archetypal perovskite MAPbI₃ (MA stands for methylammonium) yield a negative pressure coefficient for the gap of the tetragonal room-temperature phase [1], which speaks against the assumption of negligible thermal expansion effects. Here I will show that for MAPbI₃ the temperature-induced gap renormalization due to electron-phonon interaction can only account for about 40% of the total energy shift, thus implying thermal expansion to be more if not as important as electron-phonon coupling [2]. Furthermore, this result possesses general validity, holding also for the tetragonal or cubic phase, stable at ambient conditions, of most halide perovskite counterparts. As an example, I will also present recent results obtained for MA rich FA_xMA_1-xPbI₃ solid solutions, where FA stands for formamidinium.

References:

[1] Francisco López, A.; Charles, B.; Weber, O. J.; Alonso, M. I.; Garriga, M.; Campoy-Quiles, M.; Weller, M. T.; Goñi, A. R. Pressure-Induced Locking of Methylammonium Cations Versus Amorphization in Hybrid Lead Iodide Perovskites. J. Phys. Chem. C 2018, 122, 22073-22082.

[2] Francisco López, A.; Charles, B.; Weber, O. J.; Alonso, M. I.; Garriga, M.; Campoy-Quiles, M.; Weller, M. T.; Goñi, A. R. Equal Footing of Thermal Expansion and Electron–Phonon Interaction in the Temperature Dependence of Lead Halide Perovskite Band Gaps. J. Phys. Chem. Lett. 2019, 10, 2971-2977.

Acknowledgements:

We gratefully acknowledge fruitful discussions with H. Míguez, M. Calvo and A. Rubino from the Institute of Materials Science of Seville, Spain. The Spanish Ministerio de Ciencia, Innovación y Universidades is gratefully acknowledged for its support through Grant No. SEV-2015-0496 in the framework of the Spanish Severo Ochoa Centre of Excellence program and through Grant MAT2015-70850-P (HIBRI2). AFL acknowledges a FPI fellowship (BES-2016-076913) from the Spanish Ministerio co-financed by the European Social Fund and the PhD programme in Materials Science from Universitat Autònoma de Barcelona in which he is enrolled. BC and OJW thank the EPSRC for PhD studentship funding via the CSCT CDT (EP/G03768X/1, EP/L016354/1). Financial support from is also acknowledged from the European Research Council through project ERC CoG648901.

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