UCLA researchers and Ilhan Yavuz from Turkey, unraveled the surface defect-deactivation mechanism in perovskite solar cells using molecules found in tea, coffee and chocolate.
The team’s investigation was reported in the December 20, 2019 issue of the journal Science.
Professor Ken Houk and graduate student Selbi Nuryyeva collaborated with Professor Yang Yang from the Department of Materials Science and Engineering at UCLA and Professor Ilhan Yavuz (former postdoc of Houk group from 2013-2015) at Marmara University in Turkey to delineate the molecular arrangements that constructively deactivate the surface defects in perovskite solar-cells.
Highly-efficient metal-halide perovskite solar cells to date consist of polycrystalline perovskite film that often contains a high density of defects on the surface. These imperfections are the points for charge recombination, which is a major limiting factor in power conversion efficiency (PCE) and stability of perovskite solar cells. However, due to the ionic nature of the perovskite lattice, these defects can be passivated by surface treatment of perovskite with a small molecule.
In this study, Houk and collaborators explored and explained how various molecules cause passivation in perovskite solar cells. The xanthine family of molecules, namely theophylline (present in tea), caffeine (present in coffee) and theobromine (present in chocolate) were found to interact with perovskite surfaces through shape complementarity and hydrogen-bonding.
The Yang group showed that the surface treatment of perovskite using theophylline significantly increased the efficiency over that observed without theophylline. The Houk group and Yavuz then showed that to maximize the binding to surface-defects of perovskite, the amine and carbonyl functional groups have to be in an optimal configuration within the xanthine molecule relative to the surface of perovskite.
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Professor K. N. Houk, Chemistry graduate student Selbi Nuryyeva, Professor Ilhan Yavuz and Professor Yang Yang.