Semi-transparent a-SiC:H solar cells for self-powered photovoltaic-electrochromic devices

Self-powered 'smart' windows for active control of building heating and cooling represent a potential new market for amorphous-silicon based photovoltaics. Retrofit applications to existing windows are facilitated by the tandem photovoltaic-electrochromic (PV-EC) device, in which a wide-gap amorphous silicon-based alloy (a-SiC:H) photovoltaic cell is deposited together with an EC optical transmittance modulator in a monolithic coating on a single substrate. In this paper, studies of transparent wide-gap a-SiC:H thin-films and p-i-n cells designed for use in the PV-EC device are described. Using optimized a-SiC:H i-layer material, J(sc) of 3.9 mA/cm(2) and V-oc of 0.92 V is achieved, adequate to color our low-voltage Li-based EC devices in less than one minute, and good progress toward the required transparency is shown.