Computational multi-scale model for the structure of hybrid perovskites : Analysis of charge migration in novel photovoltaic materials

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http://urn.fi/URN:NBN:fi-fe201804208544
Title: Computational multi-scale model for the structure of hybrid perovskites : Analysis of charge migration in novel photovoltaic materials
Author: Järvi, Jari
Contributor: University of Helsinki, Faculty of Science, Department of Physics
Publisher: Helsingin yliopisto
Date: 2018
Language: eng
URI: http://urn.fi/URN:NBN:fi-fe201804208544
http://hdl.handle.net/10138/273522
Thesis level: master's thesis
Discipline: Theoretical Physics
Teoreettinen fysiikka
Teoretisk fysik
Abstract: Hybrid organic-inorganic perovskites (HPs) are a novel materials class in photovoltaic (PV) power generation. The PV performance of HPs is impressive, although the microscopic origin of it is not well known due to the complex atomic structure of HPs. Specifically, the disordered mobile organic cations aggravate the use of conventional computational models. I have addressed this structural complexity by developing a multi-scale model that applies quantum mechanical (QM) calculations of small HP supercell models in large coarse-grained structures. With a mixed QM-classical hopping model, I have studied the effects of cation disorder on charge mobility in HPs, which is a key feature to optimize their PV performance. My multi-scale model parametrizes the interaction between neighboring methylammonium cations (MA) in the prototypical HP material, methylammonium lead triiodide (CH3NH3PbI3, or MAPbI3). For the charge mobility analysis with my hopping model, I solved the QM site-to-site hopping probabilities analytically and computed the nearest-neighbor electronic coupling energies from the band structure of MAPbI3 with density-functional theory. I investigated the charge mobility in various MAPbI3 supercell models of ordered and disordered MA cations. My results indicate a structure-dependent mobility, in range of 50–66 cm2/Vs, with the highest observed in the ordered tetragonal phase. My multi-scale model enables the study of long-range atomistic processes in complex structures in an unprecedented scale with QM accuracy, with potential applications way beyond this study.


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