norman ferrer valls iván lópez lliberós student presentations... · electrochromic devices •is...

Norman Ferrer Valls

Iván López Lliberós

Introduction

Organic semiconductors

Electrochromic technologies

• Liquid crystal

• Liquid crystal display

• Viologen

• Viologen + TiO2

• WO3

Electrochromic applications

Conclusions

Introduction Semiconductors form the basis of electronic

devices.

Conventionally semiconductors:

• Silicon

• Germanium

• Selenium

• Aluminium

Great progress with organic and hybrid materials as

semiconductors.

Organic semiconductors

Polymers are naturally insulated.

Through the interaction of alternating single and

double bonds, is created a space between the

valence band and conduction band.

Doping: achieves the

creating of free carrier

Acting either oxidation or reduction

Radical cations or anions are formed

Doping -> Add or remove electrons in the polymer

chain through a redox reaction.

Conjugated polymers with delocalized -electron

systems behave as model organic semiconductors

Organic semiconductors

Examples:

Organic semiconductors

Apps

OSC

OLED

ELECTROCHROMIC

OFET

Organic semiconductors

Electrochromic devices • Is the reversibly ability of a material to change

its colour by an electrochemical oxidation or reduction reaction, caused by the application of an electrical potential.

Electrochromism

●“Thermochromism” and “photochromism” describe

changes of colour produced by heat and light.

Electrochromic devices

●Visible spectrum:

Transmittance (T) Reflectance (R)

Absorptance (A) Emittance (E)

When thin film of electrochromic materials are integrated in devices, it becomes possible to modulate

Electrochromic devices

●Goal -> Achieve different wavelengths associated

to variable potential.

Electrochromic devices

Electrochromic devices

Liquid crystal

Electrochromic devices

Liquid crystal display

Electrochromic devices

The image describes the synthesis

of aelectrochromic ionic liquid

(IL) based on a phosphonium core

tethered to a viologen moiety.

The electrochromic platform

exhibits a coloration efficiency of

10.72 cm2 C−1 and a varied

optical output as a function of the

incident current.

Viologen:

Electrochromic devices ● Viologen display functionalized with TiO2: an

electrochromic display based on an electrolyte

consisting of an aqueous solution of a dipositively

charged organic salt, containing a colourless cation

that undergoes a one-electron reduction process to

produce a purple radical cation, upon application of

a negative potential to the electrode.

Electrochromic devices

The device is made up of 5 layers, whose

composition is:

Plastic or glass

Conductive substrate +

Electrochromic layer

Electrolyte

Conductive substrate + Ion

storage layer

Plastic or glass

Electrochromic devices ●The nature of direct current preserves the relatively

unstable monocationic radical.

●This change in spectral features explains the

prolonged optical memory.

●This effect could be used to make a prolonged

darkened state.

Electrochromic devices

Electrochromic devices WO3 A metal cation ( Li+ normaly ) which intercalates WO3

grid when it is reduced by an applied external

voltage. Positive ions that were stored in the counter

electrode layer , cross the ion conductor layer to reach

the electrochromic material when it receives an

electrical current. This chemical reaction produces

changes in the UV - visible spectrum of WO3.

Electrochromic devices

Some applications…

Smart windows

Welding shields https://www.youtube.com/watch?v=OpZUN3dd51s

Rearview mirrors of

cars

Conclusion

ADVANTAGES DISADVANTAGES

Lifetime (cycles)

Refresh capacity

Technology

developing in

progress

Memory

Little potential for use

Pronounced optical

contrast

Reversibility

Improve the quality of

life of people in

different areas

Is everything clear or are you a little

chromic…?

Thank you!