 tungsten oxide, polyvinyl butyral, and Prussian Blue) are sandwiched by two dual layers of glass and fluorine-doped tin oxide-coated glass.Together, the tungsten oxide and Prussian Blue layers form complementary electrochromic layers; essentially, this means they form the positive and negative ends of a battery using the incoming solar energy.The polyvinyl butyral (PVB) forms the central layer in this configuration, and it serves as a polymer electrolyte (this allows for the flow of ions which, in turn, generates a current).