Collaborative Research: Development of Colloidal Group IV Doped and Alloyed Nanocrystals and Bulk- heterojunctions

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Ultra-small crystalline particles, called nanocrystals (NCs) have dimensions on the order of 0.00000005 inches, and their small size results in interesting and useful phenomena not seen in larger, macroscopic crystals. This project builds on the collaborative efforts between Susan Kauzlarich, a Chemistry professor at the University of California, Davis (UCD) and Sue Carter, a Physics professor at the University of California, Santa Cruz (UCSC) to develop new NC composites that employ nanocrystals and a organometallic film of a metal halide perovskite, where perovskite refers to the type of crystalline structure. The team designs, synthesizes and measures germanium NC individual and composite properties. The Kauzlarich lab is focused on nanocrystal synthesis and characterization of doped and alloyed germanium with the goal of controlling size, surface and shape. The Carter lab employs these nanocrystals in thin film metal halide perovskites with a focus on their optical and electron transport properties. By understanding the interfaces and electronics of the components, the PIs will judiciously combine nanocrystals with films to gain new functionality in their optical and transport properties relevant to their use as photovoltaics, with broader societal impact in electrical generation and photoelectronic device technologies. This research provides training for next generation scientists on materials synthesis, thin film fabrication, device engineering, and property measurements, advancing multidisciplinary research aligned with technology. The research will be presented at national and international meetings and the findings published in peer-review journals. In addition, UCSC and UCD faculty and students will be involved in creating curriculum and hands-on laboratories in quantum materials and printable electronics that will be offered through K-12 summer science camps and science classes.This collaborative project is focused on the development of soluble colloidal dispersions of doped and alloyed germanium (Ge) nanocrystals (NCs) with size, surface, and shape control and the fabrication and characterization of group IV bulk-heterojunctions (BHJs) to achieve control of the recombination, passivation, and charge transport. It combines the expertise of two PIs: Susan Kauzlarich, a Chemistry professor at the University of California, Davis (UCD) and Sue Carter, a Physics professor at the University of California, Santa Cruz (UCSC). This study expands the chemistry of group IV with control of surface and shape of the NCs and with fabrication of group IV bulk-heterojunctions from solutions, with a focus on control over the properties of the constituent components. As an understanding of the interfaces and relative bandgap energies is achieved, the energy levels of the Ge nanocrystals are being tuned through doping and alloying and the metal halide perovskite through lattice matching and band tuning. Several optical, electrical, and structural methods are being used to characterize these colloidal materials and their thin films. In addition to characterization methods existing in the Kauzlarich and Carter labs, collaborations on surface photovoltage (SPV) spectroscopy, ultrafast spectroscopy, Scanning Transmission Electron Holographic Microscopy, and Extended X-ray Absorption Fine Structure and X-ray Absorption Near Edge Spectroscopy (EXAFS/XANES) are enabling further characterization of the electronic and structure states of the NCs and BHJs. The PIs are judiciously combining nanocrystals with films to gain new functionality in their optical and transport properties relevant to their use as photovoltaics, with broader societal impact in electrical generation and photoelectronic device technologies. This research is providing training for next generation scientists on materials synthesis, thin film fabrication, device engineering, and property measurements, advancing multidisciplinary research aligned with technology. The research is being presented at national and international meetings and the findings published in peer-review journals. In addition, UCSC and UCD faculty and students are involved in creating curriculum and hands-on laboratories in quantum materials and printable electronics that are being offered through K-12 summer science camps and science classes.