Color Control in π-Conjugated Organic Polymers for Use in Electrochromic Devices

For almost two decades, the search of an intrinsically-conductive organic metal has represented the major driving force for research on control of the band gap of extended π-conjugated systems. However, the emergence of the application of π-conjugated oligomers and polymers in field-effect transistors, light-emitting diodes, electrochromic devices and solar cells has introduced major changes in the chemistry of gap engineering. Besides controlled band gap, active materials for electronic and photonic applications must present appropriate absorption and/or emission properties, highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energy levels and charge-transport properties. The aim of this short review is to present an overview of the recent trends in this area in order to identify possible directions for future research.

Molecular Engineering of the Band Gap of π-Conjugated Systems: Facing Technological Applications

Polyaniline film-coated electrodes as electrochromic display devices

Solid-state polymer light-emitting electrochemical cells have been fabricated using thin films of blends of poly(1,4-phenylenevinylene) and poly(ethylene oxide) complexed with lithium trifluoromethanesulfonate. The cells contain three layers:  the polymer film (as the emissive layer) and indium-tin oxide and aluminum films as the two contact electrodes. When externally biased, the conjugated polymers are p-doped and n-doped on opposite sides of the polymer layer, and a light-emitting p-n junction is formed in between. The admixed polymer electrolyte provides the counterions and the ionic conductivity necessary for doping. The p-n junction is dynamic and reversible, with an internal built-in potential close to the band gap of the redox-active conjugated polymer (2.4 eV for PPV). Green light emitted from the p-n junction was observed with a turn-on voltage of about 2.4 V. The devices reached 8 cd/m(2) at 3 V and 100 cd/m(2) at 4 V, with an external quantum efficiency of 0.3-0.4% photons/electron. The response speed of these cells was around 1 s, depending on the diffusion of ions. Once the light-emitting junction had been formed, the subsequent operation had fast response (microsecond scale or faster) and was no longer diffusion-controlled.

Polymer Light-Emitting Electrochemical Cells: In Situ Formation of a Light-Emitting p-n Junction.

http://nathan.instras.com/documentDB/paper-257.pdf

Organic electrochromic materials

Organic conducting polymers derived from substituted thiophenes as electrochromic material

Thin films of 3-4 substitued 5-membered polyhetero-cycles derived from pyrrole and thiophene have been electro-chemically synthetized, showing reversible electrochemical oxydation and reduction processes, and conductivities varying between 10−4 and 102 ω−1 · cm. The absorption spectra of their doped and undoped states, their switching time and lifetime make some of these polymers interesting for electrochromic applications.

Influence of 3-4 Substitutions On Properties of Five Membered Polyheterocycles

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. ELECTROOPTICAL PROPERTIES OF THIN FILMS OF POLYHETEROCYCLES M. Gazard, Jessica Dubois, M. Champagne, F. Garnier, G. Tourillon

M. Gazard

Papers

Organic conducting polymers derived from substituted thiophenes as electrochromic material

Influence of 3-4 Substitutions On Properties of Five Membered Polyheterocycles

Electrooptical properties of thin films of polyheterocycles