Professor James Cahoon

Professor James Cahoon
Department of Chemistry
University of North Carolina, Chapel Hill

Designing and Understanding Energy-Harvesting Materials from the Vapor Phase: From Water Splitting Single Nanostructures to Solar Absorbing Hybrid Perovskites

The vapor-phase provides a unique capacity to encode precise composition and morphology within semiconductor materials and interfaces for energy-harvesting functionality. Here, we highlight recent work on the vapor-phase synthetic control of Si nanowires, photoelectrochemical interfaces, and hybrid perovskite materials. Together, these processes provide a platform to design chemically precise, nanostructured systems for applications ranging from solar water splitting to photovoltaic solar cells. First, we introduce the vapor-liquid-solid growth process of Si nanowires and demonstrate operando pump-probe microscopy, a method that provides detailed, microscopic understanding of charge carrier drift, diffusion, recombination, and separation. Second, we discuss how abrupt transitions between p-type, intrinsic, and n-type silicon allow nanowire p-i-n superlattices to be synthesized that behave as multijunction photovoltaic devices with extraordinarily large photovoltages. Using spatioselective photoelectrochemical deposition of co-catalysts, water splitting or carbon dioxide reducing particle suspensions can be demonstrated. Third, we show how planar silicon interfaces can be functionalized with nanoscale oxide and graphene layers, facilitating the integration of molecular catalysts for solar-driven CO₂ reduction. Finally, we demonstrate the first metal organic chemical vapor deposition (MOCVD) growth of hybrid perovskite materials. Use of separate vapor precursors for the lead, organic, and halide components allows the tuning of reaction conditions to grow the material directly with high purity. Overall, the projects highlight the precise and tunable control of material composition, morphology, and functionality provided by the vapor phase.

Jim Cahoon

Prof. Jim Cahoon received his bachelor’s degree in chemistry and philosophy from the College of William and Mary in 2003 and then moved to the University of California-Berkeley to pursue a PhD in Physical Chemistry, studying the femtosecond light-driven reactions of molecules in solution with Prof. Charles Harris. In 2009, he moved to Harvard University for a post-doctoral fellowship with Prof. Charles Lieber, where he worked to develop nanostructured photovoltaic devices. In 2011, Jim started his faculty career in the Department of Chemistry at UNC Chapel Hill, being promoted to Associate Professor in 2017 and Professor in 2022, becoming the department chairperson in 2024. He has received awards including a Packard Fellowship for Science and Engineering, Sloan Research Fellowship, Cottrell Scholar Award, and UNC Phillip and Ruth Hettleman Prize for Artistic and Scholarly Achievement. He currently serves as the Executive Director of UNC’s nanofabrication and characterization facility (CHANL), UNC site director of the Research Triangle Nanotechnology Network, and thrust leader for the DOE Center for Hybrid Approaches in Solar Energy to Liquid Fuels.

Hosted by Professor Renee Frontiera