SPEAKER: Paul Haney, NIST
TITLE: Polycrystalline Photovoltaics: grain boundaries and spin-orbit coupling.
ABSTRACT: Despite decades of research, the role of grain boundaries in the photovoltaic behavior of thin film polycrystalline solar cells remains poorly understood. The complex morphology of grain boundaries and the nonlinear behavior of these materials have so far precluded an analytical description of their photovoltaic response. This in turn has hindered interpretation of experiments and efforts to optimize system design and materials. I’ll present our recent analysis in which we derive an analytical form for the dark J-V relation for a polycrystalline pn+ junction with an array of grain boundaries of varying orientation and defect structure. This relation enables an expression of the solar cell open circuit voltage in terms of grain boundary properties, which may point the way to improving this figure of merit for thin film materials such as CdTe.
The organic-inorganic lead halide perovskite is another high efficiency polycrystalline solar cell receiving much recent attention. Under conditions of reduced crystal symmetry, the perovskite is an example of a 3-d Rashba material. I’ll present our recent exploration of the spin-dependent optical response of 3-d Rashba materials, and show that this response may reveal the role of grain boundaries in photovoltaic response. I’ll finally discuss some unique aspects of the optical control of magnetism in ferromagnetic 3-d Rashba materials.
HOST: Victor Yakovenko