Accelerated computational design of hybrid organic-inorganic perovskites for photovoltaics

Significance 

In a very short time, perovskite absorbers have managed to revolutionize research on solar energy with very high solar power-conversion efficiencies. This has mainly been achieved by optimizing perovskite-film fabrication and device architecture. Recently, advances in the hybrid organic-inorganic perovskites have enabled large inorganic cations with 12-fold coordination to be replaced by organic ions, preserving the octahedral network of anions which controls the perovskite crystal structure. Such hybrid perovskites are easy to fabricate, economical and have high efficiency in converting light to electricity. Unfortunately, shortcomings related to their inherent instability upon exposure to oxygen, UV light and water among others, hinder further development of perovskite-based solar cells in the long term. Therefore, it is imperative that a novel chemical technique to stabilize these and other lead-free perovskites, preserving at the same time their excellent absorption and charge-transport properties, be developed.

Recently, Dr. Sabine Körbel and Professor Silvana Botti from the Institute for Solid State Theory and Optics at Friedrich Schiller University Jena in collaboration with Professor Miguel Marques at Martin Luther University of Halle-Wittenberg assessed the thermodynamic stability and the electronic band structures of new hybrid organic-inorganic perovskites, using a broad range of elements. Their goal was to propose viable substitutions for both lead and the organic cation that would result in enhanced thermodynamic stability, preservation of small effective masses and produce optimal band gaps for photovoltaics. Their work is currently published in the Journal of Materials Chemistry A.

The research method employed entailed a thorough consideration of compounds with the composition A+B2+X3-, where A represented the molecular organic cation, X a halogen, and B a divalent element. The researchers then adopted the most promising molecules based on previous studies. Specifically, they varied the molecule size from the very small sulfonium to the very large tert-butylammonium. Lastly, all the resulting thermodynamically stable hybrid perovskites were then further characterized by calculating their band gaps and effective masses, so as to identify the most promising candidates for further experimental and theoretical characterization.

The authors observed that there were few elements that could help in stabilizing hybrid perovskites if substituted partly for the predominant lead element. They also found out that the A site ion had potential to be used to improve stability. The researchers noted that the most promising compounds were those with methylphosphonium or sulfonium as the molecular cation and a group-IV element on the B site. This was attributed to the fact that the compounds combined to form a favorable band gap with a small effective mass.

In summary, the study presented a thorough screening of a large part of the periodic table for possible substitutions for lead, methylammonium, and iodine in methylammonium lead iodide that could enhance the thermodynamic stability of hybrid organic-inorganic perovskites. In general, they observed that their unbiased high-throughput approach had immense potential to yield unexpected compounds. Altogether, their study highlighted that the substitution of organic molecule is the most promising way to enhance thermodynamic stability, while there is no optimal replacement for lead or tin, unless one considers partial substitution or alloying.

Accelerated computational design of hybrid organic-inorganic perovskites for photovoltaics - Advances in Engineering
Reproduced from (Journal of Materials Chemistry A, 2018, volume 6, page 6463.) with permission from the Royal Society of Chemistry.

About the author

Miguel Marques received his PhD degree in Physics from the University of Wuerzburg in 2000, working with E.K.U. Gross in the field of density functional theory for superconductors. He then held everal post-doctoral positions in Spain, Germany, and in France. From 2005 to 2007 he was assistant professor au the University of Coimbra in Portugal. From 2007 to 2014 he was a CNRS researcher (CR1) at the University of Lyon 1. Since then he is a professor at the Martin-Luther University of Halle-Wittenberg. His current research interests include density functional theory, superconductivity, application of machine learning to materials science, etc. He authored 130 articles with more than 10000 citations and a Hirsch index of 48 (source: Google Scholar), and has edited three books published by Springer in their Lecture Notes in Physics series. He also has organized several summer schools and international workshops, the most relevant of which are the series of the Benasque School and International Workshop in TDDFT, that takes place in Benasque, Spain every second year.

About the author

Sabine Körbel studied Physics at the University of Münster (Germany) from 2000 to 2006 and obtained a PhD in physics from the University of Freiburg (Germany) in 2013. In her PhD thesis titled “Atomistic modeling of Cu doping in the lead-free ferroelectric potassium sodium niobate” she performed density-functional theory calculations to investigate the atomistic and lectronic structure of a perovskite considered for use in piezoelectric applications.

During postdocs at the Institut Lumière Matière of the Université Claude Bernard Lyon 1 (France) and at the Institute of Condensed Matter Theory and Solid State Optics of the Friedrich Schiller University of Jena (Germany), she studied optical absorption of semiconductor crystals and nanoparticles using many-body perturbation theory, and performed high-throughput calculations of inorganic and hybrid organic-inorganic perovskites for photovoltaic and other applications.

In a postdoc at the Institute of Physics of the Czech Academy of Sciences and currently in a Marie-Skłodowska-Curie fellowship at the School of Physics of Trinity College Dublin (Ireland) she investigates the interactions between ferroelectric domain walls and charge carriers in BiFeO3 (http://ferrovolt.simplesite.com/).

She published 16 peer-reviewed articles, for which Google Scholar lists about 300 citations in total.

About the author

Professor Silvana Botti holds the chair of Solid State Theory at the Friedrich-Schiller University Jena. After receiving a PhD in Physics from the University of Pavia in Italy, she joined the Ecole Polytechnique, University of Paris-Saclay, first as Marie-Curie Fellow (2002-2004) and then as CNRS research scientist (2004-2008). She worked then as a CNRS researcher at the University of Lyon (2008-2014).

Her research goals extend from the development of many-body treatments for theoretical spectroscopy of complex materials, to crystal structure prediction and high-throughput computational materials design using machine learning. She authored more than 90 articles in international peer-reviewed journals and is Associate Editor for npj Computational Materials.

Her recent studies focus on the search of new materials for energy production, storage and saving.

Reference

Sabine Körbel, Miguel A. L. Marques, Silvana Botti. Stable hybrid organic–inorganic halide perovskites for photovoltaics from ab initio high-throughput calculations. Journal of Materials Chemistry A, 2018, volume 6, page 6463.

Go To Journal of Materials Chemistry A

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