Understanding highly mobile excitons in halide perovskites

University Of California-Davis, Davis CA

Investigators

Abstract

Nontechnical description A new family of materials, called halide perovskites, have recently received much attention because of their truly promising potentials for cost-effective applications in solar cells, as well as light emitting devices. Light can excite an electron to higher energy, leaving an electron vacancy or a hole in these materials. The oppositely charged electron and hole are attracted to each other and can be bound into a pair, often referred to as an exciton. How well these excitons move in the halide perovskites is critical to optimize their applications but is poorly understood. Preliminary results from the research team suggest these excitons can be highly mobile in these materials. In this project, the principal investigator aims to apply novel spatially and temporally resolved experimental techniques to illustrate the physical mechanisms of the formation and transport of excitons in halide perovskites. The project will open up new opportunities by taking advantage of excitons in halide perovskites for novel electronic applications. This project will also educate and train undergraduate and graduate students, including underrepresented minority students, in the rapidly advancing nanoscale and energy sciences. The principal investigator plans to prepare students with the skills and knowledge to pursue research and development in novel materials and photovoltaics with industrial partners. Technical description Excitons are often given negative connotation in solar energy harvesting in part due to their presumed short diffusion lengths. Contradicting this, the research team has recently demonstrated carrier diffusion lengths up to 200 micrometers in halide perovskites, implying that exciton transport may not limit the energy conversion process in these materials. Based on these exciting preliminary results, the project aims to understand highly mobile excitons as well as the strong spin-orbit coupling effects on exciton transport, in both three-dimensional and low-dimensional single-crystal halide perovskite nano- and micro-structures. The project will investigate single-crystal halide perovskite field effect transistors with comprehensive temperature-dependent spatially, energetically, and temporally resolved optoelectronic techniques. Temperature dependent photocurrent mapping will provide direct measurements of exciton and free carrier diffusion lengths in various halide perovskite compounds with different excitonic binding energy and cation electric dipoles. Pump-probe photocurrent measurements will be used to determine exciton lifetime and diffusivity with high time resolution. Rashba-Dresselhaus effects in halide perovskites will be investigated by circular photogalvanic effect and surface magneto-optical Kerr effect with high spatial resolution. Low dimensional halide perovskites with strong quantum confinement and anisotropic optical transition will also be studied with the developed methodology. 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.