Big Advantages of Going Small: Nanostructured Perovskite-phase Cesium Lead Iodide: Nano Seminar Series

Seminar | October 26 | 2-3 p.m. | 390 Hearst Memorial Mining Building

 Prof. Aaron Fafarman, Drexel University, Chemical Engineering

 Berkeley Nanosciences and Nanoengineering Institute

Perovskite-phase cesium lead iodide (CsPbI3) possess three almost too-good-to-be-true properties for photovoltaic and electroluminesence applications and one Achilles heel: it is not stable under ambient conditions. This talk will provide an introduction to CsPbI3, highlighting our contributions to identifying and understanding some of its remarkable chemical, physical and functional properties.

Using time-resolved transient terahertz spectroscopic measurements of the kinetics of charge-carrier recombination, we have constructed a numerical model of the dominant recombination mechanisms. The kinetic parameters thus obtained provide evidence that CsPbI3 shares two features found in its much more well studied cousins, the hybrid organic/inorganic lead iodide perovskites: spin- and momentum-forbidden radiative recombination and an extraordinarily low defect-assisted recombination rate due to apparently benign defect chemistry. The existence of forbidden radiative recombination in an all-inorganic perovskite decisively refutes the importance of the organic component to this phenomenon in the hybrid variants.

Using differential scanning calorimetry, we quantitatively measured the thermodynamics of the phase change that defines the problematic instability of the desired metastable perovskite phase, identifying a purely catalytic destabilization effect of atmospheric moisture. We detail a novel approach to stabilizing the functional metastable phase using co-assembly of CsPbI3 and CsPbCl3 nanocrystals, followed by chemical sintering into thin films.

"Nanocrystal substitutional doping" in this manner creates a composite material that is more stable by at least two orders-of-magnitude, suggesting that the metastability of CsPbI3 may yet prove surmountable. A hypothesis to account for the stabilization effect of nanostructuring will be presented, with significant implications beyond CsPbI3.

Aaron Fafarman did his BS here at UC Berkeley (Go Bears!) and PhD ('10) at Stanford where he won the Linus Pauling Teaching Award. After a postdoc in EE at Penn, he joined Drexel in 2014.