We report on the first monolithic, amorphous-silicon-based, photovoltaic-powered electrochromic window coating. The coating employs a wide bandgap a-Sil-xCx:H n-i-p photovoltaic (PV) cell as a semitransparent power supply, and a LiyWO3/LiAlF4/V205 electrochromic (EC) device as an optical-transmittance modulator. The EC device is deposited directly on top of a PV device that coats a glass substrate.
The a-Sil-xCx:H PV cell has a Tauc gap of 2.2 eV and a transmittance of 60 to 80% over a large portion of the visible light spectrum. We reduced the thickness of the device to about 600 Å while maintaining a 1-sun open-circuit voltage of 0.9 V and short-circuit current of 2 mA/cm2.
Our prototype 16 cm2 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 electrochromic device are approximately 1 minute under normal operating conditions (±1 volt).