LEAPS-MPS: Time- and depth-resolved charge carrier transport in phase stable hybrid perovskites

Wesleyan University, Middletown CT

Investigators

Abstract

NON-TECHNICAL SUMMARY Mixed halide perovskites are a novel class of hybrid semiconductors with organic and inorganic components. They have shown great promise for use in solar cells and light-emitting diodes, in part due to their highly tunable electronic and optical properties. However, fundamental limitations have limited their use. In particular, stability issues due to ion migration and phase segregation must be resolved. Complicating studies of pervoskites is the dynamic time scale of electronic processes. These span from picosecond electron scattering, nanosecond energy relaxation, to millisecond ionic motion. This LEAPS-MPS project will use terahertz waves that are sensitive to electron conduction to find pathways to develop stable hybrid perovskites. To achieve this goal, the PI will develop new non-contact terahertz characterization techniques to increase the probing window from picosecond to millisecond time scales. THz studies will be complemented by photoluminescence and X-ray characterization to investigate the dynamic coupling among electronic, optical, and structural properties. The PI emphasizes training for next generation scientists, involving undergraduate and graduate student researchers will be involved in the project. In addition, the PI leads the Girls in Science Camp for elementary school girls, with a team of female faculty members, high school, and college teaching assistants. Through intergenerational mentoring, this project contributes to the training of next-generation scientists and educators. TECHNICAL SUMMARY Recent developments in organic-inorganic hybrid perovskites have opened a wide range of opportunities for highly tunable materials. However, thermodynamically driven halide segregation in mixed-halide perovskites changes their optical and optoelectronic properties. Ionic motion also impacts material properties occurring in a solid, requiring a broad range of time scales to understand dynamic material properties. This LEAPS-MPS project seeks to develop depth- and time-resolved, non-contact characterization techniques to study the impact on charge carrier transport by the movement of halide ions upon light soaking and to find pathways to develop phase-stable hybrid perovskites. To achieve this goal, the PI will develop new optical pump, terahertz probe techniques using a ns-pulsed pump laser with electronic timing to extend the measurement time-window from 2 ns to beyond 1 ms to match carrier recombination dynamics and increase the dynamic probing window. THz studies will be complemented by time- and spatially-resolved photoluminescence and in situ X-ray scattering mapping to provide correlations with the local film stress and composition. Ultimately, this project will link picosecond carrier scattering, nanosecond recombination, and millisecond ionic motion to provide a comprehensive understanding of photocarrier dynamics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.