MRS Meetings and Events

 

CH03.16.02 2022 MRS Spring Meeting

The Kinetics and Mechanisms of Light-Induced Phase Separation in a Mixed-Halide Perovskite

When and Where

May 25, 2022
9:30pm - 9:45pm

CH03-Virtual

Presenter

Co-Author(s)

Siying Peng1,2,Yanming Wang3,Michael Braun1,Yikai Yin1,Andrew Meng4,Balreen Saini1,Wanliang Tan1,Kayla Severson1,Ann Marshall1,Katherine Sytwu5,John Baniecki1,Jennifer Dionne1,Paul McIntyre1

Stanford University1,Westlake University2,Shanghai Jiao Tong University3,University of Pennsylvania4,Lawrence Berkeley National Laboratory5

Abstract

Siying Peng1,2,Yanming Wang3,Michael Braun1,Yikai Yin1,Andrew Meng4,Balreen Saini1,Wanliang Tan1,Kayla Severson1,Ann Marshall1,Katherine Sytwu5,John Baniecki1,Jennifer Dionne1,Paul McIntyre1

Stanford University1,Westlake University2,Shanghai Jiao Tong University3,University of Pennsylvania4,Lawrence Berkeley National Laboratory5
Mixed halide perovskites are promising materials for enabling optoelectronic devices with high quantum efficiency and low cost. The composition of both the cation and anion (halide) sublattices of perovskite crystals can be manipulated over a wide range to engineer their light absorption and emission behavior. However, halide ion phase separation is a barrier for the application of mixed-halide perovskites in solar cells and LEDs, whereby the presence of large populations of photo-generated or injected carriers causes undesirable changes of the local bandgap. Structural changes consistent with phase separation of mixed-halide perovskite alloys has been observed by X-ray diffraction. It was hypothesized that the phase separation mechanism involves a self-reinforcing demixing of Br- and I- ions driven by the reduced potential energies of photogenerated carriers that trap in regions of smaller band gap. Subwavelength imaging has been performed to visualize the process in single crystalline and poly-crystalline organic perovskites. While several works have shown improvements of stability with respect to halide ion phase separation, there are several poorly understood aspects such as whether it occurs via spinodal decomposition or by nucleation and growth, the length scale for composition fluctuations, their time dependence and the self-limiting (or saturating) nature of the phase separation on optoelectronic properties of the mixed halide alloys.<br/>We investigate the mechanism of phase separation in CsPbI<sub>x</sub>Br<sub>3-x</sub> perovskite single crystals driven by absorption of band gap light. We visualize the phase separation process and its dynamics at the nanoscale at -100 <sup>o</sup>C using <i>in situ </i>STEM-CL, where formation of iodide-rich regions is detected via locally red-shifted emission. We probe how the phase separation rate can be modulated by the intensity of illumination and the temperature. Combined with phase field modeling that accounts for the coupling between electronic and chemical driving forces, our observations of light-induced phase separation in halide perovskite point to a spinodal decomposition-like mechanism combined with coarsening, in which both the amplitude of composition fluctuation and the characteristic length scale grows non-linearly with time. Our findings provide insights that may assist in further engineering mixed-halide perovskites either for stability or for intentional programming of the local halide ion composition, opening pathways for a wide range of applications.

Keywords

in situ | perovskites | scanning transmission electron microscopy (STEM)

Symposium Organizers

Leopoldo Molina-Luna, Darmstadt University of Technology
Ursel Bangert, University of Limerick
Martial Duchamp, Nanyang Technological Universisty
Andrew Minor, University of California, Berkeley

Symposium Support

Bronze
DENSsolutions BV
MRS-Singapore
Quantum Detectors Ltd

Publishing Alliance

MRS publishes with Springer Nature