L. Kullman

Recent advances in electrochromics for smart windows applications

Electrochromic smart windows are able to vary their throughput of radiant energy by low-voltage electrical pulses. This function is caused by reversible shuttling of electrons and charge balancing ions between an electrochromic thin film and a transparent counter electrode. The ion transport takes place via a solid electrolyte. Charge transport is evoked by a voltage applied between transparent electrical conductors surrounding the electrochromic film/electrolyte/counter electrode stack. This review summarizes recent progress concerning: (i) calculated optical properties of crystalline WO3, (ii) electrochromic properties of heavily disordered W oxide and oxyfluoride films produced by reactive magnetron bias sputtering, (iii) novel transparent reactively sputter-deposited Zr–Ce oxide counter electrodes and (iv) a new proton-conducting antimonic-acid-based polymer electrolyte. Special in depth presentations are given on elastic light scattering from W-oxide-based films and of electronic band structure effects affecting opto–chronopotentiometry data in Zr–Ce oxide. The review also contains some new device data for an electrochromic smart window capable of very high optical transmittance.

Sputter-deposited nickel oxide for electrochromic applications

Thin films were produced by sputtering of metallic Ni in Ar/O-2 and Ar/O-2/H-2 atmospheres. Systematic studies of these films were carried out in electrochromic devices with tungsten oxide and e ...

Towards the smart window : progress in electrochromics

Electrochromic devices have the ability to produce reversible and persistent changes of their optical properties. The phenomenon is associated with joint ion and electron transport into/out of an electrochromic thin film, in most cases being a transition metal oxide. This paper outlines the various applications of such devices in smart windows suitable for energy-conscious architecture, in variable-reflectance mirrors, and in display devices. Critical materials issues and design concepts are discussed. The paper also covers two specific research topics: computed electronic structure of crystalline WO3 incorporating ionic species, showing how reflectance modulation emerges from a first-principles calculation; and Li+ dynamics in heavily disordered Ti oxide, illustrating how diffusion constants derived from impedance spectroscopy can be reconciled with the Anderson—Stuart model.

Electrochromic devices embodying W oxide/Ni oxide tandem films

Six-layer electrochromic devices of indium tin oxide (ITO)/NiOxHy/WO3/ZrP-electrolyte/WO3/ITO were made by reactive dc magnetron sputtering and lamination. The WO3 layer between the acidic ZrP-based electrolyte and the NiOxHy layer served as optically passive protective layer. The optical inactivity of the protective layer could be understood from arguments based on electron density of states.

Ozone coloration of Ni and Cr oxide films

Films of Ni and Cr oxide were made by reactive DC magnetron sputtering. Ozone exposure, obtained by ultraviolet irradiation in the presence of oxygen, gradually induced coloration in the initially transparent films. Electrochemical measurements correlated the optical absorption with a charge deficiency in the film. Our results demonstrate a convenient technique for treating the counter electrode in a W-oxide-based electrochromic device prior to device assembly.

Transparent ion intercalation films of Zr–Ce oxide

Zr–Ce oxide films were made by reactive dc magnetron cosputtering. The elemental composition was determined by Rutherford backscattering spectrometery and the crystalline structure by x-ray diffraction. Li intercalation/deintercalation was accomplished potentiodynamically in a liquid electrolyte. The films remained fully transparent irrespective of their degree of lithiation, which may be reconciled with a population/depopulation of Ce 4f levels.

Decreased electrochromism in Li-intercalated Ti oxide films containing La, Ce, and Pr

Films of Ti–La oxide, Ti–Ce oxide, and Ti–Pr oxide were produced by reactive dc magnetron sputtering. Their composition was determined by Rutherford backscattering spectrometry. X-ray diffractometry and infrared absorption spectroscopy indicated that the microstructure was heavily disordered and in most cases Ti-oxidelike. Electrochemical Li intercalation/deintercalation was studied by cyclic voltammetry, and ensuing optical data were recorded by spectrophotometry. Ce addition diminished the electrochromism, and films with Ce/Ti atom ratios exceeding 0.3 were almost fully transparent irrespective of their lithiation, pointing at the potential applications of such films as counter electrodes in transparent electrochromic devices. The optical and electrochemical data were discussed in terms of a model based on electron insertion/extraction in 4f states located in the gap between the valence and conduction bands of CeO2.

Optical and electrochemical properties of dc magnetron sputtered Ti-Ce oxide films

Reactive dc magnetron sputtering was used to make mixed Ti–Ce oxide films with a Ce/Ti ratio γ between 0 and 0.6. Their optical and electrochemical properties were strongly dependent on the composition. Films with 0.3<γ<0.6 were optically passive under charge insertion, which makes them suitable as counterelectrodes in transparent electrochromic devices.

Optical and electrochemical properties of Li+ intercalated Zr–Ce oxide and Hf–Ce oxide films

Sputter deposited Zr–Ce oxide and Hf–Ce oxide films were investigated with regard to structure, optical absorption, and electrochemical properties. X-ray diffractometry and Rutherford backscattering spectrometry showed that polycrystalline Zr–Ce oxide and Hf–Ce oxide films had cubic crystal structures for 40–100 mol % CeO2 and 50–100 mol % CeO2, respectively. Cyclic voltammetry was performed in an electrolyte of propylene carbonate containing LiClO4. The charge capacity was ∼60 mC/cm2μm for a Zr–Ce oxide film with a Ce/Zr atom ratio of ∼13 as well as for a Hf–Ce oxide film with a Ce/Hf atom ratio of ∼2. A decrease of the charge capacity was noted after ∼1000 voltammetric cycles, with the mixed oxide films being far more stable than CeO2. In situ optical transmittance measurements showed that both Zr–Ce and Hf–Ce oxide films remained essentially transparent during Li+ intercalation. Chronopotentiometry measurements were used to elucidate effects of the electronic structure during Li+ intercalation.

Zr-Ce Oxides as Candidates for Optically Passive Counter Electrodes

Abstract Zr–Ce oxide films with compositions from pure Zr oxide to pure Ce oxide were made by reactive DC magnetron co-sputtering. The composition and structure were determined by Rutherford backscattering and X-ray diffraction. Pure Ce oxide films have high charge capacity and are optically passive under charge insertion; they are, however, chemically unstable in an electrolyte of LiClO 4 in propylene carbonate. Pure Zr oxide has practically zero charge capacity. Zr–Ce oxide films have high (above 80%) optical transmittance, high charge capacity, and good chemical stability. These films remain fully transparent irrespective of their degree of lithiation, which may be reconciled with electrons accommodating 4f states of Ce.