GOALI: Doping Control and Processes in Metal Halide Perovskites

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Nontechnical Description: Metal halide perovskites refer to a class of semiconductors that have recently achieved an exceptional rate of performance improvement for use in light-emitting devices, photodetectors and solar cells. The combination of excellent performance and facile solution processing open new opportunities for low-cost high-performance electronic devices. While these materials have enjoyed extensive success for application in electronic devices, further improvement is limited in part by a lack of understanding of how to control the number of electrical carriers within the semiconductor (known as doping), which is a vital parameter for establishing device operation. By creating a broadly interdisciplinary project, employing both theory and experimental approaches, the current research seeks to develop a better understanding of doping processes for controlling the level of electrons/holes within this important class of halide perovskites. By achieving the goals of the project, novel designs of higher-efficiency solar cells and light-emitting devices, as well as higher-performance perovskite transistors are expected. Undergraduate, graduate and postdoc researchers play a pivotal role in the multidisciplinary project execution and the project therefore plays a vital role in training future scientists. As a GOALI project, a critical aspect involves broadening student experiences to include industrial research exposure, as well as creating a link to the world-leading materials characterization capabilities within industry. Technical Description: Semiconductor doping using intrinsic/extrinsic crystalline defects establishes the energy levels and carrier densities that determine optoelectronic properties. High-performance photovoltaic materials, for example, rely on careful doping control to modify the electronic properties and improve the device performance to levels approaching the Shockley-Queisser limit. Although metal halide perovskites have received much attention recently, due to the exceptional rise in associated photovoltaic performance, the current understanding and exploration of doping in this class of complex ionic semiconductors remains limited. This project paves the way for more tunable functional halide perovskites by addressing important doping related questions, such as: (1) can the relatively 'soft' nature of metal halide perovskites create special challenges and opportunities for development of new doping pathways; (2) can the use of complexes rather than individual ions enhance doping tenability; and (3) what opportunity for molecular doping exist within the organic cation layer versus impurity doping within the metal halide framework? In order to develop this critical understanding, the project integrates academic and industrial research in materials synthesis, optoelectronic characterization and theory to investigate dopant incorporation and activation in perovskite semiconductors. The research consists of several thrusts, including: (1) theory/computation-guided development of new dopants and doping processes, (2) exploration of molecular dopants in hybrid perovskites, (3) manipulation of radiative recombination using doping and (4) application of unique electrical transport characterization tools, developed by the industrial partner, to understand doping in halide perovskites and also to provide a framework for future study of transport phenomena in complex materials.