Since their discovery by Deb [1] at the end of the sixties, great advancements have been achieved in the development of real-world applications for electrochromic devices. Nevertheless, a rapid commercialization of smart windows still suffers from issues such as limited durability, neutral color, flexibility, switching speed, etc… Herein, improvements of full EC device will be discussed, focusing on the study of two layers, namely the counter electrode and the transparent electrode. For the latter, aiming at growing devices on flexible substrate, particular attention will be devoted to the deposition at low substrate temperature (T < 150 °C) of ZnO based thin films using the PLD technique. Enhancement of the electrical properties was achieved by Si doping, leading to SZO (ZnO:Si) thin films exhibiting resistivity as low as 3 E-4 Ωcm. For the counter electrode approach, improved durability of NiO thin films was successfully achieved by three approaches, : (i) by adding another element/oxide such as Li favouring a disordered structure, (2) by embedding NiO particles into a Zn2+-doped TiO2 matrix, leading to a new composite or (3) by preparing carbon containing film. The latter leads to NiO-C thin films maintaining extremely good cyclability up to 25 000 cycles associated with a contrast ratio of 2.8. Finally, the performances of full devices will be investigated. [1] S.K. Deb, Appl. Opt., Suppl. 3, 192, 1969.

A switchable mirror has been investigated and developed for use as a new energy-saving window. In the developed mirrors, an elecrtochromic device has a multilayer of Mg-Ni/Pd/Al/Ta2O5/HXWO3/indium tin oxide on a substrate. The device can alter its optical properties reversibly between the transparent and reflective states by applying a voltage. Conventional windows are often affected by environmental factors such as temperature and humidity. In the viewpoint of commercial use, we investigated the effects of the environment on the optical switching properties of the device by an accelerated degradation test using a thermostat/humidistat bath with constant temperature and constant relative humidity. The typical results showed that the device never showed its optical switching properties in the test for long time. The Mg-Ni layer on the device showed a rough surface and changed into a non-metallic state of oxide and hydroxide analyzed by X-ray photoelectron microscopy. To avoid the problem in the environment, a device with a surface coating layer was also developed. The device with the surface coating layer had its optical switching properties in hard environment.

Current state of the art energy-efficient electrochromic windows and advanced battery technologies rely on the transport of lithium ions. To assess the durability and cycling performance of these devices, it is important to accurately quantify the concentration and distribution of the Li ions. Due to their light atomic mass and low weight percentage present in these materials many conventional analytical techniques such as XPS, AES and EDX lack the sensitivity and depth resolution to accurately quantify their concentration. Nuclear Reaction Analysis (NRA) is a promising technique to accurately quantify the concentration of Li within electrochromic window and battery-related materials. This technique involves a nuclear reaction under resonance conditions. When the energy of the accelerated ions is carefully tuned to the resonance energy of the target element of interest, an "amplification" of the elemental signal is obtained. Unlike traditional Rutherford Back-Scattering (RBS), this technique is particularly sensitive to light elements and in conjunction with RBS, it can also produce a depth of profile as well as atomic concentration.In this contribution, we will briefly discuss the concept of NRA and present examples of how it can be used to study the lithium concentration in electrochromic window and battery materials.This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Due to the electrochemical nature of electrochromic devices, two electrodes must be present in any configuration. Reduction or oxidation at one electrode can stimulate color changes: the function of the opposite electrode must be, at least, to complete the overall redox reaction. Requirements for this electrode include charge balancing, avoiding undesirable reactions. Choosing adequate materials could enhance the device performance, while the wrong choice can be damaging in terms of lifetime and optical properties. Different options have been considered; probably the most widespread two consist on the use of an optically passive ion storage layer or the use of a complementary electrochromic layer. Both of them aim to increase stability and lifetime, although the former does not contribute to the optical performance. Benefits expected from the later include better optical response as two layers are simultaneously changing color.Our group showed recently that the dual (or complementary) configuration for electrochromic devices, widely used, has some optical limitations (J. Padilla et al., Electrochem. Commun. 10 (2008) 1-6). Specifically, this configuration cannot increase the maximum contrast achievable by one of the materials alone. This suggests the use of a transparent complementary material to overcome this limitation. Recent papers describe the synthesis of new transparent materials and their inclusion in electrochromic devices with this objective (M. A. Invernale, et al., Chem. Mater. 21 (2009) 3332-33369; S.V.Vasilyeva et al., ACS Applied Materials & Interfaces 1 (2009) 2288-2297), but synthesizing transparent conducting materials requires considerable effort.In this work, we propose an alternative route to obtain a transparent ion storage layer, simply changing two parameters: charge and surface ratio between the electrodes of a device. We show proofs of concept for this new proposal. Results indicate that it could be applied to a new configuration for electrochromic devices that will show maximum contrasts.(Acknowledgements: MICINN CSD2007-00007, CARM-D429-2008, F. Seneca 11955/PI/09)

Transparent conducting oxide (TCO) films are important components of a variety of electro-optic devices, including electrochromic (EC) windows, displays, light-emitting diodes, and photovoltaics. While they are generally very durable, they can be damaged by exposure to potentials outside their stability range, especially reducing potentials that can irreversibly convert the transparent phases to absorbing decomposition products. This is critical in the case of lithium ion devices, as reduction to metals may begin at potentials of 1 V vs. Li/Li+. This can lead to degradation in conventional EC devices when they are driven by too large a potential to increase switching speed or to access their maximum dynamic range. Even proton-based ECs can suffer some damage.For reflective devices based on metallic antimony alloy films [1] that become transparent on lithium insertion at ca. 0.8 V, the use of currently available TCOs is prohibited. Alternatives such as printed metal or carbon stripes and grids, as well as nanotube or graphene layers are not yet available. We have, therefore, investigated the application of a thin, transparent amorphous carbon barrier to allow electrons to flow to and from the EC active layer(s) while blocking Li ion transport into the TCO. The films were applied by cathodic arc deposition to commercial ITO coated glass substrates [2,3]. It was necessary to achieve a compromise between the transparency, conductivity, and ion-blocking properties of the carbon films. Pinholes and other defects are readily identified by polarization to 0.5 V in a liquid lithium electrolyte. By varying the deposition conditions, it was possible to reduce or eliminate electrolyte penetration of the barrier layer and protect the underlying ITO from damage.REFERENCES[1] G. Liu and T. J. Richardson, Solar Energy Materials & Solar Cells 86 (2005) 113-121.[2] J.L. Endrino, D. Horwat, R. Gago, J. Andersson, Y.S. Liu, J. Guo, A. Anders, Solid State Sciences 11 (2009) 1742-1746.[3] S. Sansongsiri, A. Anders, B. Yotsombat, Diamond & Related Materials 17 (2008) 2080-2083.

A recent focus on the enhancement of energy efficiency for buildings has generated new interest on the development of fast switching and durable electrochromic windows. Investigation of antimony doped tin dioxide nanocrystalline films[1] has demonstrated electrochromic properties in the near infrared region of light. In order to enhance the ability to tune spectroelectrochemical characteristics across the near infrared while substantially maintaining transparency to visible light, we prepared nanostructured films of indium tin oxide (ITO) and aluminum zinc oxide (AZO) from solvent dispersions of colloidal nanocrystals. Using a combination of scanning electron microscopy, X-ray diffraction, cyclic voltammetry, spectroelectrochemical analysis, and Hall effect measurements, we correlate the morphological and the electrochromic properties of our nanocrystal films. For example, preliminary results on nanostructured ITO films show a ~20% change in transmittance for near infrared light (λ=1900nm) with only a ~0.1% change in the visible transmittance (λ=500nm) for a ~150nm film. In addition, both AZO and ITO films demonstrate a strongly capacitive electrochemical response that is repeatable for multiple cycles. Overall, both material systems explored in this paper demonstrate the potential to use nanostructured transparent conducting oxide materials for near infrared electrochromic applications. [1] zum Felde, U., et al., J. Phys. Chem. B, 2000, 104 (40), 9388-9395.