Stand-alone photovoltaic-powered electrochromic smart window

Three different, innovative approaches have been taken to develop photovoltaic (PV) integrated electrochromic (EC) devices for smart-window applications. These are: (i) a stand-alone, side-by-side PV-powered EC window; (ii) a monolithically integrated PV-EC device; and (iii) a never photoelectrochromic device based on a dye-sensitized TiO2 solar cell. The compatibility of PV-EC devices has been analyzed: and the potential for large energy savings for building applications has been suggested. The first monolithic, amorphous-silicon based, PV-powered electrochromic window is described in detail. The device employs a wide bandgap a-Si1-xCx/H n-i-p PV cell as a semitransparent power source, and a LiyWO3/LiAlF4/V2O5 EC device as an optical-transmittance modulator. The EC device is deposited directly on top of a PV cell that coats a glass substrate. The a-Si1-xCx/H PV cell has a gap of 2.5 eV and a transmittance of 60-80% over a large portion of the visible light spectrum. Our prototype 16-cm(2) PV-EC device modulates the transmittance by more than 60% over a large portion of the Visible spectrum. The coloring and bleaching times of the EC device are approximately 1 min under normal operating conditions (+/- 1 V). A brief description of photoelectrochromic windows based on a combination of dye-sensitized TiO2 and WO3 EC-layer is also given. Published by Elsevier Science Ltd.