Tunable photovoltaic electrochromic device and module

An innovative tunable photovoltaic electrochromic (PV–EC) device concept, in which planar distribution of silicon thin film solar cells (Si-TFSCs) structure with successively deposited electrochromic thin films (ECTFs) and electrolyte layer is demonstrated. The switching mechanism of a PV–EC device is realized by electrically separating the electrodes of the Si-TFSCs and ECTFs, and the connection of the two systems is achieved through an external switching apparatus that links each Si-TFSC and ECTF through one transparent conductive oxide (TCO) layer. According to the PV–EC device structure, Si-TFSCs arranged in stripes makes large area module fabrication feasible, while Si-TFSCs arranged in arrays allows pixel structure design possible. When illuminated by sunlight under short-circuit condition, the photopotential outputted from a single Si-TFSC drives ECTF layer to change color, simultaneously a portion of the photocurrent is stored in a capacitor. Once the ECTF is tinted, no power is needed to retain its colored state due to the bi-stable property of the electrochromic material. In order to revert the PV–EC device to its bleached state, the capacitor supplies reverse potential to cause discoloration of the ECTF. In addition, the monolithically integrated Si-TFSC module generates electricity to a connected load. In view of photoelectric conversion and optical modulation properties, the PV–EC device can both function as a Si-TFSC module and as a self powered smart glass, which has great advantages in green energy application.