Demonstration of an Integrated Inorganic-Organic IoT-Enabled System With PV and Electrochromic Devices for Autonomous Smart Windows

Smart windows may incorporate integrated stacks of photovoltaic and electrochromic devices, whose opacity/transparency can be synergistically modulated (and/or wirelessly controlled) by autonomously generated voltages. This article demonstrates a proof of concept of an Internet of Things (IoT)-enabled system comprised of an integrated bulk (organic) heterojunction photovoltaic device with an (inorganic) electrochromic device. First, fully organic (poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2 -thienyl-2',1',3'-benzothiadiazole)]:phenyl-C71-butyric-acid-methyl) photovoltaic devices were fabricated, and their performance were evaluated with respect to optical transparency and power conversion efficiency (PCE). Upon varying the hole transport layers and substrates, the strongest performing devices exhibited a PCE of 3.2%, an open-circuit voltage (V_{\text{oc}}) of 0.9 V, and a short-circuit current (J_{\text{sc}}) of 10-15 mA/cm^{^{2}}. Second, tungsten trioxide WO_{3} electrochromic films were inkjet printed on conductive and transparent ITO-coated PET substrates of varying mechanical flexibility, including PDMS with a network of embedded Ag nanowires and indium- tin-oxide-coated polyethylene terephthalate. The printed electrochromic devices demonstrated clear switching behavior under external bias, with a coloration time of 8 s, a bleaching time of 12 s, and an optical modulation of 0.5874 at \lambda = 525 nm. Finally, the photovoltaic and electrochromic devices were connected, with a network configuration of the former to provide requisite autonomous power for the demonstration of opacity modulation (or light transmission properties) of the latter, utilizing a Particle IoT controller that was switched wirelessly with a smartphone.