21 February 2019
Probing the molecular influence on hybrid perovskite
Published online 28 June 2015
Scientists look deep inside the molecular structure of hybrid perovskite, a promising new material for solar energy.
It took only five years for scientists to improve the efficiency of a solar energy cell incorporating hybrid perovskite material from than 20% from 3.8% in 2009 to more than 20% today. The efficiency of silicon – the established material currently used in solar cells – has barely increased from 25% in the past 15 years.
Now, researchers are exploring hybrid perovskite at a molecular level hoping to learn enough to harness its full potential.
Despite their efficiency, hybrid perovskites have been shown to be unstable in humid conditions, and also contain lead, a toxic element, explains computational physicist Fadwa El-Mellouhi from Qatar Environment and Energy Research Institute (QEERI). “To design stable perovskite without lead, scientists need first to understand how these materials work.”
So a team of scientists from QEERI in Doha and Trinity College in Dublin used computational quantum mechanical modeling to investigate the structure of lead methylammonium triiodide perovskite: a compound arranged in a crystal-like structure formed of the organic molecule, methylammonium, and an inorganic semiconducting crystal, lead triiodide.
In their quest to understand how hybrid perovskite’s electronic and optical properties work in harvesting and converting solar energy into electricity, they found that the two components of the material played complementary roles. The inorganic lead triiodide portion of the perovskite crystal is responsible for capturing light. Meanwhile, the orientation of the organic portion of the compound enhances the lifetime of photo-excited electrons, supporting their collection into electricity and increasing the photovoltaic efficiency of the hybrid perovskite.
“What makes this material different from other solar harvesting materials,” explains El-Mellouhi, “is that the electronic structure of these hybrid crystals is altered because of the thermally-induced motion of the [organic] molecules.” This ultimately favours electron transport and collection as a photocurrent.
QEERI’s materials scientist Nouar Tabet says that while silicon’s properties are very well understood, more knowledge is needed on perovskite’s molecular structure causes it to perform so well so materials engineers can design solar cells with optimal properties for solar conversion..
The team plans on continuing its computer simulation modelling to learn more about hybrid perovskite’s molecular structure and function and to experiment with material synthesis. “Now that we understand how these new materials work, we can design new compounds to use for solar energy harvesting at a smaller cost than silicon solar cells,” says El-Mellouhi.
Motta, Carlo et al. Revealing the role of organic cations in hybrid halide perovskite CH3NH3PbI3. Nat. Commun. http://dx.doi.org/10.1038/ncomms8026 (2015)