Wide-gap, transparent amorphous silicon based photovoltaics can be integrated with electrochromic materials to produce a self-powered 'smart' window coating. Existing electrochromic window designs require an external electrical connection, which may be economically unfeasible. This problem is solved by the tandem photovoltaic-electrochromic (PV/EC) device, in which a wide-gap amorphous silicon-based alloy (a-SiC:H) photovoltaic device is deposited together with an electrochromic optical transmittance modulator in a monolithic device on a single substrate. In this paper, we discuss our proposed monolithic photovoltaic-electrochromic device. We also present studies of transparent, wide-gap (Tauc gap of 1.8 to 2.2 eV) amorphous silicon-carbon thin films and p-i-n devices designed for use in the photovoltaic-electrochromic device. The photovoltaic cells in the PV-EC can operate at low current (< 1 mA/cm2) because a total injected charge of only 60 (mu) C/cm2 will darken the EC layer to a visible transmission of 5%, but they will need a high open-circuit voltage (> 1.0 V) and high transparency (approximately equals 70%). We describe our progress toward these design targets.
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