(51c) Symbiotic Pairing of Near-UV Solar Cells with Electrochromic Windows for Visible Light and Heat Management in Architectural Applications

Energy use in residential and commercial buildings comprises about 40% of energy demand today and 30% of energy-related carbon emissions in the United States, with heating accounting for nearly twice the energy required for cooling and lighting combined. Increasing building energy efficiency will shave peak demands for electricity. In my talk, I will highlight our development of solar-powered electrochromic windows that can be integrated into windows to reduce electricity consumption.

The solar-powered electrochromic window comprises a polyelectrochromic conducting polymer that is optically transparent in its reduced state and dark blue in its oxidized state. Integration with a semitransparent organic solar cell provides the necessary power to switch between its transparent and colored states. Unique to this approach is our use of a single-junction organic solar cell. By designing and using materials that absorb exclusively in the ultra-violet and near-visible as the photoactive layers in our solar cells, the resulting devices exhibit open-circuit voltages that are unprecedented for single-junction organic devices (> 1.4 V). As such, we are able to drive switching of the electrochromic window without the need to construct solar cells with complex tandem architectures. Importantly, the active layers of our devices are pinhole- and defect-free. Coupled with inherently low resistive power losses, the photocurrents are scalable with the footprint of solar cells while our devices retain high fill factors. Whereas device optimization of typical solar cells to increase photovoltage has almost always come at the expense of decreasing photocurrents, the scalability of photocurrents in our devices has enabled us to break this paradigm. We can tune device photovoltage per application needs through judicious selection of the donor/acceptor materials pair whose optoelectronic properties can be tuned via molecular design, and access the necessary photocurrents by fabricating arbitrarily large devices.