Cu2Zn(Sn,Ge)S4 Nanocrystal-Ink Based Solar Cells: Colloidal Nanocrystal Growth and Control of Electrically Active Traps

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PI: Hugh W HillhouseProposal Number: 1133671Intellectual MeritSolar energy is an abundant and promising renewable energy resource for the generation electricity. However, the realization of solar photovoltaics (PV) for achieving a sustainable energy future will require low-cost and earth-abundant elements for PV materials which offer high solar energy conversion efficiency. In this regard, Copper-Zinc-Tin-Sulfur/Selenide (CZTSSe) is emerging as top candidate PV material, but suffers from low solar energy conversion efficiency because the electronic trap states cannot be controlled through current PV layer fabrication approaches. The proposed research will engineer a colloidal nanocrystal-ink route to yield dense CZTSSe layers with low concentrations of electrically-active traps to yield high quality optoelectronic films with low rates of non-radiative recombination that offer potentially high efficiencies which approach theoretical limits. In the nanocrystal-ink route for fabrication of CZTSSe layers, colloidal nanocrystals will be synthesized and then suspended in an ink that is coated on substrate. The nanocrystal layer is then sintered to yield a high quality dense polycrystalline photoabsorbing layer for the solar PV cell. Strategies to control CZTSSe nanocrystal growth with surfactants, solvents, and ligands that do not yield electrically active traps will be identified through a suite of measurements, including small-angle x-ray scattering (SAXS), in-situ UV-Vis-NIR spectroscopy of the nucleating and growing nanocrystals, and photoluminescence of the nanocrystals and sintered films. Furthermore, a unique ultrasonic spray deposition strategy will be developed to form films with a well defined lateral composition gradient, as small differences in the absorber layer composition can have a profound effect on the electronic quality. The spatial photovoltaic properties will then be screened with spatially resolved photocurrent measurements to identify favorable defect chemistries, and operating solar cells will be fabricated and tested from the most promising compositions. Broader ImpactsIn addition to training graduate students, the proposed activities will engage the public and K-12 students in solar energy topics. A graduate student working through the Society of Women Engineers will mentor local elementary school students with science fair projects. The PI work will with the Pacific Science Center in Seattle to create clean energy demonstrations, make presentations through the Science Cafe program, and mentor local high school teams to prepare projects for Solar Day, which is being held in Seattle in conjunction with the 50th Anniversary of the IEEE Photovoltaics Specialists Conference.