G. Foley

Thin film solid state ionic materials for electrochromic smart windowTM glass

Abstract The optical transmissivity (and especially the reflectivity) of a multilayer electrochromic smart winow TM glass structure can be reversibly modulated by an electrical current pulse; and the modulation is spectrally selective. This is important forbuilding and vehicle windows and for other electro-optical applications. Thin film solid state ionic materials are the key elements of such a structure. Their roles and some of their current states of development at Tufts (and particularly the state of developent of the electrochromic layer) are discussed. Also discussed is the state of development of prototype all solid electrochemically reversible, five-layer window devices. These devices employ: a lithium-insertable rf sputter-deposited polycrystalline WO 3 film that exhibits reflection modulation as the electrochromic layer, a lithium-inserted rf sputter deposited In 2 O 3 film or a thermally deposited V 2 O 5 film as the counterelectrode layer; an rf sputter deposited LiNbO 3 film as the ion conducting (solid electrolyte) layer; and rf sputter deposited ITO (Sn-doped In 2 O 3 ) or undoped In 2 O 3 films as the transparent conducting layers. The devices exhibit useful operating characteristics and indicate that robust and economical practical smart window TM glass could soon become a commercial reality.

Recent research related to the development of electrochromic windows

Abstract The results of recent research on each of the layers of a solid-state multilayer structure for electrochromic windows are reviewed. This includes a review of the requirements of the multilayer structure for building windows and especially the need to have an electrochemically balanched system. The results indicate that excess free electron scattering in polycrystalline WO 3 films (the electrochromatic layer) is not only the source of lower than desired reflectivity modulation, but it is also the major source of higher than desired absorptivity modulation. Research on LiAlF 4 indicates that it is a viable candidate for the ion conducting layer, being a good lithium ion conductor and a good electronic insulator. Finally, we have recently discovered that tin-doped and undoped In 2 O 3 films are mixed conductors, exhibiting lithium ion injection/extraction. This is significant since such films could possibly serve in the dual capacity of counterelectrode and transparent conductor, thereby reducing the complexity, the technical problems, and the cost of electrochromic window assemblies.

Electrochromic behavior in ITO and related oxides.

Electrochromic properties, are reported for thin films of the transparent conducting oxides In/sub 2/OCd3:Sn are doped SnO/sub 2/.

Further evidence for free electrons as dominating the behavior of electrochromic polycrystalline WO3 films

The results of two types of experiments on electrochromic (poly)crystalline films of rf sputtered WO3 are presented as additional new evidence that the behavior (especially scattering) of the free electrons plays a dominant role in the electrochromic properties of such films.

Optical frequencies free electron scattering studies on electrochromic materials for variable reflectivity windows

Abstract Electrically variable reflectivity electrochromic windows have the potential to significantly reduce heating and cooling loads in buildings. The importance of reducing the optical frequencies free electron scattering in the variable reflectivity electrochromic layer will be shown. Based on spectroscopic ellipsometry studies and an analysis of the dynamical resistivity of polycrystalline films of colored WO3 and of single crystals of NaxWO3, it is tentatively concluded that the principal source of free electron scattering in WO3 films is structural disorder, and probably crystallographic shear planes which act as monopolar dislocations. This is in contrast to the much higher reflectivity of single crystal tungsten bronzes for which the more dominant scattering mechanism appears to be that associated with ionized impurities. We therefore conclude that it should be possible to improve the reflectivity modulation in films of electrochromic WO3, and consequently that a practical variable reflectivity electrochromic window should be achievable.

Completely solid lithiated smart windows

The optical transmissivity (and especially the reflectivity) of a multilayer electrochromic smart window® glass structure (patents applied for) can be reversibly modulated by an electrical current pulse; and the modulation is spectrally selective. This is important for building and vehicle windows and for other electro-optical applications. Discussed is the state of development of each of the layers for, and the state of development of, prototype all-solid electrochemically reversible, 5-layer Smart Window devices. These devices employ: a lithium-insertable RF sputter-deposited polycrystalline WO3 film that exhibits reflection modulation as the electrochromic layer; a lithium-insertable RF sputter-deposited In2O3 film or a thermally deposited V2O5 film as the counterelectrode layer; an RF sputter-deposited LiNbO3 film as the ion conducting (solid electrolyte) layer; and RF sputter-deposited ITO (Sn-doped In2O3) or undoped In2O3 films as the transparent conducting layers. The devices exhibit useful operating characteristics and indicate that robust and economical practical smart window® glass could soon become a commercial reality.

Thin films of WO3 for practical electrochromic windows

Abstract It is shown that practical spectrally-selective transmittance modulation can be achieved with thin (50–100 nm) WO3 films, and therefore such films should be useful for fabricating electrochromic windows. The transmittance and reflectance modulation results are compared with theoretical predictions. The results indicate an excess intraband absorbance, which is attributed to free electron scattering arising from extended defects.

Prototype All-Solid Lithiated Smart Window Devices

The optical transmissivity (and especially the reflectivity) of a ultilayer electrochvomic smart windowTM glass structure can be reversibly modulated by an electrical current pulse; and the modulation is spectrally selective. This is important for building and vehicle windows and for other electro-optical applications. Discussed is the state of development of each of the layers for, and the state of development of, prototype all-solid electrochemically reversible, 5-layer smart window devices. These devices employ: a lithium-insertable rf sputter-deposited polycrystalline WO3 film that exhibits reflection modulation as the electrochromic layer; a lithium-insertable rf sputter deposited In203 film or a thermally deposited V205 film as the counterelectrode layer; an rf sputter deposited LiNbO3 film as the ion conducting (solid electrolyte) layer; and rf sputter deposited ITO (Sn-doped In203) or undoped In203 films as the transparent conducting layers. The devices exhibit useful operating characteristics and indicate that robust and economical practical smart windowTM glass could soon become a commercial reality.

Characterization Technique For Transparent Ion Conducting Films

In the development and production of transparent multilayer solid-state ionic structures, and in particular, electrochromic Smart Window the measurement of electron and ion transport properties of the layers is essential, since it can determine the feasibility as well as the speed of operation of devices with those layers. We are developing a novel electro-optical technique to measure the ion and electron mobilities of several layers of the electrochromic Smart WindowTM glass essentially in situ. Presented in this paper are the technique, preliminary models, and transport properties of two such films.

Optical Frequencies Free Electron Scattering Studies On Electrochromic Materials For Variable Reflectivity Windows

Electrically variable reflectivity electrochromic windows have the potential to significantly reduce heating and cooling loads in buildings. The importance of reducing the optical frequencies free electron scattering in the variable reflectivity electrochromic layer will be shown. Based on spectroscopic ellipsometry studies and an analysis of the dynamical resistivity of polycrystalline films of colored W03 and of single crystals of NaxW03, it is tentatively concluded that the principal source of free electron scattering in W03 films is structural disorder, and probably crystallographic shear planes which act as monopolar dislocations. This is in contrast to the much higher reflectivity single crystal tungsten bronzes for which the more dominant scattering mechanism appears to be that associated with ionized impurities. We therefore conclude that it should be possible to improve the reflectivity modulation in films of electrochromic TM), and consequently that a practical variable reflectivity electrochromic window should be acriievable.