Perovskite solar cells can be cheaper and easier to produce compared to silicon solar cells, but they lack long-term stability, and this has hindered their progress. The most-studied perovskites for solar applications comprise a negatively charged lead-halide inorganic skeleton, partnered with positively charged organic cations, such as methylammonium (MA) or formamidinium (FA). These combine in a highly regular atomic arrangement.
The lead halide component is mainly responsible for interacting with light, while the organic component provides structural stability, but both are relatively unstable, which has restricted their commercial development.
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Further reading
- Fluoride ions add layer of defence to perovskite solar cells
- Perovskite process boosts solar cell efficiency and lowers fabrication costs
- Perovskite process boosts solar cell efficiency and lowers fabrication costs
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Now, Udo Schwingenschlögl from the KAUST Solar Centre, and his Ph.D. student, Aleksandra Oranskaia have used computational modelling examined the organic component of solar perovskite materials, looking for ways to improve the stability of FA-lead halide perovskites. Their results are published in Advanced Energy Materials.
“Our motivation was to apply new computational methods to one of the hottest problems in the field of perovskite solar cells,” Oranskaia said in a statement.
Experimental studies have shown that FA-based perovskites are more stable than MA, so the team first compared MA and FA bonding strengths, focusing on noncovalent forms of bonding, such as hydrogen bonding. They then looked at whether adding other organic "dopants" into the FA-lead halide perovskite structure could enhance stability even further.
“We showed for the first time that the noncovalent bonding strength of organic cations can be used to improve hybrid perovskite materials,” Schwingenschlögl said. Although covalent bonds are the strongest, other types, including hydrogen bonding and halogen bonding between the organic cation dopants and the lead halide component, help to stabilise the perovskite structure.
“We show that doping with organic cations of the right volume and shape - those that bond more strongly than FA to the inorganic skeleton via hydrogen and halogen bonding - can stabilise the material,” Oranskaia said. Organic cations with covalently and noncovalently bound chlorine atoms or ions proved to be particularly effective: they helped to suppress damaging halide movements known as X-migrations.
“This offers a strategy to boost the performance of lead halide solar cells,” Schwingenschlögl said
The team next plans to study the effects of noncovalent interactions on the phase stability of other solar-related materials.
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