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Halide Perovskites: Advanced Photovoltaic Materials Empowered by a Unique Bonding Mechanism

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Schoen, Carl-Friedrich 
Schumacher, Mathias 
Robertson, John 
Golub, Pavlo 


jats:titleAbstract</jats:title>jats:pOutstanding photovoltaic (PV) materials combine a set of advantageous properties including large optical absorption and high charge carrier mobility, facilitated by small effective masses. Halide perovskites (ABXjats:sub3</jats:sub>, where X = I, Br, or Cl) are among the most promising PV materials. Their optoelectronic properties are governed by the BX bond, which is responsible for the pronounced optical absorption and the small effective masses of the charge carriers. These properties are frequently attributed to the jats:italicn</jats:italic>sjats:sup2</jats:sup> configuration of the B atom, i.e., Pb 6sjats:sup2</jats:sup> or Sn 5sjats:sup2</jats:sup> (“lone‐pair”) states. The analysis of the PV properties in conjunction with a quantum‐chemical bond analysis reveals a different scenario. The BX bond differs significantly from ionic, metallic, or conventional 2c2e covalent bonds. Instead it is better regarded as metavalent, since it shares about one p‐electron between adjacent atoms. The resulting σ‐bond, formally a 2c1e bond, is half‐filled, causing pronounced optical absorption. Electron transfer between B and X atoms and lattice distortions open a moderate bandgap resulting in charge carriers with small effective masses. Hence, metavalent bonding explains favorable PV properties of halide perovskites, as summarized in a map for different bond types, which provides a blueprint to design PV materials.</jats:p>


Funder: Deutsche Forschungsgemeinschaft; Id:


effective mass, halide perovskites, metavalent bonding, optical absorption, photovoltaics

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Aachen University (RWTH0508, JARA0183, JARA0198)
Federal Ministry of Education and Research (16ES1133 K)
Walloon Region (1117545, J.0154.21)