(63c) Conducting-Polymer Electrochromic Windows Powered by Transparent Single-Junction Organic Solar Cells

Lighting and cooling accounts for 20% of the energy consumption of residential and commercial buildings in the United States. Reducing energy needs associated with lighting and cooling will shave electricity peak demands and increase building efficiencies. In my talk, I will highlight the demonstration of a solar-powered electrochromic window that can be integrated into windows to increase building energy efficiency.

The solar-powered electrochromic window comprises a polyelectrochromic conducting polymer that is 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 the use of a single-junction organic solar cell. By using materials that absorb exclusively in the ultra-violet and near-visible as photoactive layers of 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 the inherently low resistive power losses in our devices, our device currents are scalable with areal coverage with minimal losses to device fill factor and maximum power. While device optimization of typical solar cells to increase photovoltage has almost always come at the expense of photocurrents, the scalability of photocurrents in our devices has allowed us to break this paradigm. We can tune the photovoltage per application needs through judicious selection of the donor/acceptor materials pair having prescribed energy levels and access the desired current levels by fabricating arbitrarily large devices.