FIP Seminar Student Speaker Awardee: Reversible crystal-glass switching and underlying transformation kinetics in hybrid perovskites

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Wed, 03/01/2023 - 12:00 to 13:00

Akash Singh


Akash Singh, PhD Candidate, MEMS, Duke University

Metal halide perovskites (MHPs) are the widely celebrated family of crystalline semiconductors that has led to momentous advancement in the fields of photovoltaics, emitters, and sensors. Though most of the research is condensed towards studying the crystalline MHPs, the study of MHPs that can access a glassy/amorphous state could provide unique opportunities to extend the associated structure-property relationships and broaden their application space. Despite significant efforts to amorphize MHPs under high pressure, an immediate reversal to a crystalline state upon pressure removal has so far impeded the study of the glassy MHP state and the associated practical applications, thus necessitating alternative routes. Further, the ability to melt-quench hybrid MHPs has largely been limited due to (i) the significant decomposition of the organic component upon heating at elevated temperatures and (ii) the super-fast ordering kinetics of these melts. Drawing inspiration from the structure-property studies of chiral vs. racemic organic systems, herein, we demonstrate the first example of glass formation in a hybrid MHP at ambient pressure along with reversible switching between glassy and crystalline states.

In addition, the underlying thermodynamic and kinetic effect of glass crystallization is studied using iterative calorimetric experiments and numerical modeling techniques, to extract the activation energy (~350 kJ/mol) and Avrami parameter (~2), which suggests a heterogeneous surface-mediated nucleation mechanism with 2D crystal growth, as also corroborated by in-situ and ex-situ microscopy. Formation of a semiconducting MHP glass, along with the demonstration and study of the kinetics of reversible switching between the glassy and crystalline states, each offering distinct semiconducting properties, unlocks a new research domain for MHPs with numerous prospective applications spanning the research fields of memory, computing, photonics, and meta-surfaces.

Akash is a 4th year Ph.D. candidate working in David Mitzi’s energy materials lab at Duke University. Recently, Akash and his colleagues have pioneered the field of glass-forming metal halide perovskites, a family of semiconducting materials traditionally known to exist only in crystalline states. Currently, his work involves understanding the structure and fundamental properties of glassy states in perovskites as well as expanding their application space beyond the traditionally celebrated fields of photovoltaics, emitters, and sensors. Before coming to Duke, Akash majored in mechanical engineering at IIIT Jabalpur and carried out his undergrad thesis work on the development of cost-effective perovskite solar cells at Centre for Nanoscience and Engineering, IISc Bangalore.