Stand-alone photovoltaic-powered electrochromic smart window

Abstract

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 novel photoelectrochromic device based on a dye-sensitized TiO 2 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-Si 1− x C x /H n–i–p PV cell as a semitransparent power source, and a Li y WO 3/LiAlF 4/V 2O 5 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-Si 1− x C x /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 TiO 2 and WO 3 EC-layer is also given.