Electrochromic Devices

Having been actively involved in application of electrochromics, the Sotzing group is adept at the construction of electrochromic devices. Through an Army sponsored program in collaboration with the Electronic Sensors and Night Vision Division (Dr. R. Draper and Dr. M. Wood) and Triton Systems, Inc. (K. Mahmud and Dr. B. Radmard) and in collaboration with experts in physical chemistry and electrochemistry (Prof. T. Otero and Dr. J. Padilla) at Centro de ElectroQuímica y Materiales Inteligentes de la UPCT, thousands of devices have been assembled and tested. At right is an assembled electrochromic eyepiece for helmet mounted display application.

This electrochromic device consists of two electroactive polymer layers with one being poly[biphenylmethyloxymethylenemethyl-3,4-propylenedioxythiophene] (ProDOT) which serves as the primary electrochromophore and a thin layer of 3,6-bis(3,4-ethylenedioxythienyl)-1-methylcarbazole which serves as a complementary anodically coloring electrochromophore and ion storage layer.

Our standard electrochromic cell consists of seven layers and can be constructed to be a see through window, or a reflective device depending upon the choice of material for each layer. Typically for a window, layers 1 and 7 are either glass or polyethyleneterphthalate. Further, incorporation and preliminary testing of polycarbonate have been performed in our labs. Both layers 2 and 6 are indium doped tin oxide, and the electroactive polymer is coated onto this layer. Finally, a solution is applied to one substrate and then sandwiched between both, and UV cured to provide a solid-state electrolyte to complete the electrochromic device. This polymer based electrolyte has been tested using propylene carbonate and various ionic liquids as plasticizers to enhance switching speeds at room temperature and at temperatures tested as low as -30 ^OC.

Average specs of electrochromic devices based on Poly(ProDOT):

Photopic Transmission:
~ Bleached 70%
~ Colored 28%
Switching Time:
~ 1 second at room temperature
~ 1,000,000 cycles w/ 2% loss in photopic contrast
Power Requirements:
~ 1.5 mW/cm²
Memory:
~ 2 days after switching off, best device is 2 months
Temperature Range:
~ Device is tested operational between -30 to 50^OC
Storage:
~ Storage temperatures as high as 100^OC have been tested

Photopic Transmission can be varied by varying electrochromic polymer film thickness. For sunglass application photopic transmission can be from 60% in bleached state to 15% in the colored state.

Through the program with the Army, an electrochromic device incorporated into a pair of sand-wind-dust goggles behind ballistic polycarbonate was constructed and is shown top of page. These goggles have a control at the side for dial in control of electrochromic transmissivity. Our group continues to build electrochromic devices tailored for specific application. For our latest venture in electrochromic devices visit Chromic Decor.

For further information on these electrochromic devices and our capability contact Professor Sotzing.