Takaya Kubo

Electrochemical properties of non-conjugated electrochromic polymers derived from aromatic amine derivatives

Abstract The electrochemical and optical properties of two types of non-conjugated electrochromic polymers derived from aromatic amine derivatives (DDP-A, DDB-P) are presented. DDP-A is synthesized by the polymerization of N , N ′-dimethyl- N , N ′-diphenyl-1,4-phenylenediamine (DDP) and acetaldehyde (A), and DDB-P is polymerized with N , N ′-dimethyl- N , N ′-diphenylbenzidine (DDB) and propionaldehyde (P). Both DDP-A and DDB-P have a band gap in the ultraviolet region, and are colorless and transparent in neutral states. At one-electron oxidation states, DDP-A + absorbs light mainly in a visible region, whereas DDB-P + absorbs light mainly in a near-infrared (NIR) region. DDP-A + and DDB-P + are nitrogen-centered π-bridged mixed-valence compounds showing intervalence-charge transfer bands. The electrochemical and optical properties of DDP-A and DDB-P depend on the nitrogen–nitrogen distance correlating the electronic coupling of nitrogen redox centers. From the standpoint of energy saving, DDB-P is very interesting because it absorbs light in an NIR region. Finally, focusing on the smart window application, the optical properties of the solid-state electrochromic cell fabricated with DDP-A and heptyl viologen are examined. The cell was confirmed to be colored blue by applying a potential of about 1.0 V, and bleached at 0 V.

Nanostructured Organic Bulk Heterojunction Solar Cells

Publisher Summary This chapter deals with the nanostructured organic bulk heterojunction solar cells. More than three decades of research on organic solar cells based on π-conjugated materials has led to steadily increasing efficiency of solar cells. This chapter focuses on small molecular organic materials and their solar cells comprise three sections: (1) photophysical properties of organic p-conjugated materials; (2) characteristics of simple bulk heterojunction solar cells; and (3) characteristics of hybrid-type heterojunction solar cells. The hybrid bulk heterojunction (HH) solar cell was shown to have a high conversion efficiency compared to the heterojunction (PH) and bulk heterojunction (BH) solar cells. Moreover, there is a possibility that applying anti-reflecting coatings to the tandem cell could increase efficiency to over 6%. This chapter explains the design of the BH solar cell structure that has been discussed so far by focusing on the exciton diffusion and charge carrier collection efficiencies only. The product of the four key factors, ηA × ηED ×ηCT × ηCC, determines the conversion efficiency of an organic solar cell. Therefore, all four quantum efficiencies must be optimized to achieve conversion efficiency in excess of 10–15%. New donor and acceptor materials must be tailored to have optimum energy levels of highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO and LUMO) so that the materials can absorb a broader solar-spectral region and have lower exciton-binding energy. This continuous and fundamental research will mark a new epoch in organic solar cells, which are expected to offer low-cost solar energy conversion and be environmental friendly.

Durability of electrochromic windows fabricated with carbon-based counterelectrode

A tungsten oxide film has been widely employed as an electrochromic material dye to its great electrochemical durability. Durability of carbon materials as electrodes have been more clearly verified in many practical use, a lithium ion battery and an electric double layer capacitor, for example. We then focused on a large electric double layer capacitance and the electrochemical durability in carbon materials. The chief purpose of this paper is to examine electro-optical performance and durability of the electrochromic windows (ECW) fabricated with the carbon- based electrode. The ECWs have been tested for durability under various weather conditions. Most of the tests were carried out on the ECWs with UV-cut filters installed. The filters allowed us to improve the ECW durability greatly. Main results are as follows: (1) we were successful in developing carbon-based electrodes for ECWs and in fabricating an ECW (a carbon-based electrode/a polymeric solid electrolyte/a tungsten oxide electrode), (2) the utilization of the carbon-based electrode increased the ECW durability against high temperature, UV radiation, heat cycle and so forth, and (3) their electrochromic performance were found out to be sufficiently high enough for architectural and automotive purposes.