The present project is a continuation of a research project on "smart" windows started during the previous JOULE-1 Programme (JOUE-CT90-0045). It seeks to show the feasibility of controllable light transmission through a window glazing. This new concept consists in a solid state variable transmission device based on the phenomenon of electrochromism. The device would be electrically activated and capable of controlling the visible as well as the near infrared parts of the solar spectrum.
Medium to large scale variable transmission windows (100-900 cm'#y) will be manufactured and tested.
The success of a cost-effective variable transmission electrochromic device will greatly depend on the possibilities of manufacturing a solid state thin film device with a life-time in excess of 40000 cycles and light modulation of 50% . This specification imposes great demands on such an electrochemical system and requires the development of highly stable thin films, capable of inserting ions (e.g. Lithium) to levels of 10-15 atomic percent. Additionally, a solid state (polymer) electrolyte is required with a formulation such as to give stable ion conduction over a wide range of temperatures (-20C to 85C) without undergoing electrochemical decomposition and gas evolution.
The present research team has been engaged in this field for the previous three years and has shown that a five layer device
(Glass-TCO-EC-PE-CE-TCO-Glass, with TCO (transparent conductive oxide)=ITO, EC(electrochromic layer)=WO3, PE=Polymer Electrolyte and CE
(counter-electrode)=NIOx,TiOx) can be constructed showing good cycling stability (20000-30000 cycles) with light modulation of 40%.
This new stage (phase II) will continue the improvement of coating performance by fine tuning deposition parameters and optimizing device manufacturing (Pilkington). The formulation of the polymer will be changed to take into consideration the operating requirements of such devices and our improved understanding of device operation, the role of this layer and its interaction with the other elements of the device. Particular attention will be paid to the mechanical and electrochemical stability as well as its performance in the presence of small amounts of moisture. New materials, in particular for the electrochromic part, will be investigated. Intercalation mechanisms and driving procedures for electrochemical stability will form a key part of the programme. Finally optical and thermal performance will be assessed by developping suitable models taking into account the dynamic behaviour of the electrical and optical properties of the complete devices as well as that of each component.
Funding SchemeCSC - Cost-sharing contracts
5260 Odense S
OX3 0BP Oxford - Headington
SO17 1BJ Southampton