Novel Self-Powered Electrochromic Materials and Devices

Self-powered electrochromic device is a kind of instrument that can change transmittance with the electricity converting from solar energy. A novel derivative of triphenylamine, (4-((4-(dimethylamino)phenyl)(phenyl)amino)benzyl) phosphoric acid (TPAPA), with both photovoltaic and electrochromic functions, is designed and synthesized in this work. Working electrode was made by dissolving the compound in chloroform and then coating the solution on titanium dioxide-coated fluorine-doped tin oxide glass. The working electrode shows light yellow at -1.5 V and dark green at +2.5 V. The maximum transmittance contrast between the two states is 64.2% at 629 nm. Meanwhile, the photovoltic properties of TPAPA-based electrochromic devices were measured with a solar simulator under 1-sun illumination. Energy conversion efficiency of 0.32% was obtained, with short-circuit current density of 1.32 mA/cm², open-circuit voltage of 0.44 V and fill factor of 0.54. Our results suggest that the compound has dual functions of electrochromism and photovoltaics. Compared with conventional photoelectrochromic devices with both photovoltaic and electrochromic electrodes, the dual functional TPAPA-based device provides much simple strcuture, and thus may have potential application in buildings, vehicles and displays.