How do OLEDs work?

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everyonemines
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How do OLEDs work?

Postby everyonemines » Thu Jul 09, 2009 6:19 am UTC

I understand protonation and deprotonation in liquids. I get charge transport in silicon, and semiconducting polymers. What I don't understand is how charge is transferred between molecules in an OLED.

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Charlie!
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Re: How do OLEDs work?

Postby Charlie! » Thu Jul 09, 2009 6:29 am UTC

The old fashioned way. With enough energy, an electron will go ANYWHERE :P It's nigh identical to metallic semiconductors: once the electron has above a certain energy, it can move freely among molecules along some of a bajillion different routes.

Classically, I suppose you could imagine it flying off one atom and sticking to another. But quantumly it's just popping into existence wherever it pleases (within the semiconductor), with an "orbital" that spans a whole lot of molecules.
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everyonemines
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Re: How do OLEDs work?

Postby everyonemines » Thu Jul 09, 2009 6:31 am UTC

No, that's dielectric breakdown and tunneling, respectively. You appear to be describing metals as having bandgaps. No, electron transport cannot be described as an electron flying off from one thing to another, except in the case of electron guns.

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Charlie!
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Re: How do OLEDs work?

Postby Charlie! » Thu Jul 09, 2009 8:21 pm UTC

everyonemines wrote:No, that's dielectric breakdown and tunneling, respectively. You appear to be describing metals as having bandgaps. No, electron transport cannot be described as an electron flying off from one thing to another, except in the case of electron guns.

Why is it dielectric breakdown to describe moving from a valence orbital to the conduction band? Is it dielectric breakdown for a silicon semiconductor to work? (and yes, I just described a metal as having a bandgap. Silicon, probably doped with some more metals. I mean, fine, "metalloid," but whatever.)

As for tunneling, it's a similar effect (via quantum mechanics being weird), but tunneling refers to jumping through classically forbidden regions. At high enough energies (a couples of electron volts), the routes between molecules are no longer classically forbidden and being on another molecule becomes much more likely.

Also, electron transport can be described as an electron flying off one thing and sticking to another if someone asks "What I don't understand is how charge is transferred between molecules" and you get the urge to include the classical picture :P


But given your tone, it doesn't seem like I answered your question. Could you maybe try again?
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mattdude
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Re: How do OLEDs work?

Postby mattdude » Thu Jul 09, 2009 9:23 pm UTC

OLEDs work exactly the same way as LEDs except they use either organic molecules or organic polymers. organic meaning contains carbon. the wiki page has a pretty decent explanation of LEDs, so that would be a good start.

everyonemines
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Re: How do OLEDs work?

Postby everyonemines » Fri Jul 10, 2009 2:45 am UTC

In LEDs, charge is moving through a crystal, while in OLED it's moving between organic molecules. There is obviously some kind of special process, because OLEDs require specific molecules. How is the charge transferred between the molecules?

Brwagur
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Re: How do OLEDs work?

Postby Brwagur » Fri Jul 10, 2009 2:50 am UTC

The organic molecules must be conjugated polymers, mustn't they?
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everyonemines
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Re: How do OLEDs work?

Postby everyonemines » Fri Jul 10, 2009 3:00 am UTC

I understand how conductivity in polymers works, but OLEDs use smaller molecules.

mattdude
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Re: How do OLEDs work?

Postby mattdude » Fri Jul 10, 2009 6:38 am UTC

everyonemines wrote:I understand how conductivity in polymers works, but OLEDs use smaller molecules.


that's actually not necessarily true. if you'd read the wiki article, you'd have found out that polymers are used in some OLEDs. in fact, polymers are required in OLEDs to make the cooler ones. they suspend the polymers in water because they are soluble, and then the polymer-water solution is used as ink in a normal inkjet printer. this allows for them to be printed on large screens, as well as flexible plastics. small molecules are usually deposited on glass substrates due to their process known as vacuum deposition. blah blah blah i'm not going to regurgitate the article, read up on it. but don't stop there. the important thing to note is that with all of these, one side has a different fermi level than the other side--like any other diode. LEDs for further viewing on generally how LEDs work...

enjoy, if you have any further questions feel free to post, someone here if not myself will try to help you out.

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Charlie!
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Re: How do OLEDs work?

Postby Charlie! » Fri Jul 10, 2009 8:54 am UTC

everyonemines wrote:In LEDs, charge is moving through a crystal, while in OLED it's moving between organic molecules. There is obviously some kind of special process, because OLEDs require specific molecules. How is the charge transferred between the molecules?

The special process is having an electron with enough energy. To span intermolecular distances. That's it.

There seem to be two main reasons why special molecules are needed.
1) need free charges to be stable at reasonable energies, usually done with big ol' aromatic systems in the molecules.
2) need to select molecules that will emit visible light with their transition. Can't just throw in whatever, need to make a fairly narrow range of colors.
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everyonemines
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Re: How do OLEDs work?

Postby everyonemines » Fri Jul 10, 2009 9:56 am UTC

Charlie! wrote:
everyonemines wrote:In LEDs, charge is moving through a crystal, while in OLED it's moving between organic molecules. There is obviously some kind of special process, because OLEDs require specific molecules. How is the charge transferred between the molecules?

The special process is having an electron with enough energy. To span intermolecular distances. That's it.


Since you keep giving me inaccurate answers, I'll ask something more specific: What is the nature of the interactions in the types of charge transfer complexes formed by the types of molecules used in OLEDs?

Mr_Rose
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Re: How do OLEDs work?

Postby Mr_Rose » Fri Jul 10, 2009 4:12 pm UTC

everyonemines wrote:
Charlie! wrote:
everyonemines wrote:In LEDs, charge is moving through a crystal, while in OLED it's moving between organic molecules. There is obviously some kind of special process, because OLEDs require specific molecules. How is the charge transferred between the molecules?

The special process is having an electron with enough energy. To span intermolecular distances. That's it.


Since you keep giving me inaccurate answers, I'll ask something more specific: What is the nature of the interactions in the types of charge transfer complexes formed by the types of molecules used in OLEDs?

How do you know with such certainty that the answer is inaccurate, given that you are the one that does not know how OLEDs work?
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Charlie!
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Re: How do OLEDs work?

Postby Charlie! » Fri Jul 10, 2009 9:06 pm UTC

everyonemines wrote:
Charlie! wrote:
everyonemines wrote:In LEDs, charge is moving through a crystal, while in OLED it's moving between organic molecules. There is obviously some kind of special process, because OLEDs require specific molecules. How is the charge transferred between the molecules?

The special process is having an electron with enough energy. To span intermolecular distances. That's it.


Since you keep giving me inaccurate answers, I'll ask something more specific: What is the nature of the interactions in the types of charge transfer complexes formed by the types of molecules used in OLEDs?

No idea. In part since it's the same molecule acting as both a donor and an acceptor in all interactions, and since it's an interaction that only vaguely resembles classical charge transfer until the electron gets observed, my limited knowledge of inorganic chemistry is insufficient to even know if the question has meaning. I'm more used to thinking with orbitals (or quantum states :P ).

Sorry.
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opsomath
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Re: How do OLEDs work?

Postby opsomath » Thu Jul 30, 2009 8:53 pm UTC

I think the OP might be confusing organic semiconductors/conductors with OLEDs? The latter meaning a light-emitting diode made from the former?

If I'm right, organic semiconductors roughly speaking work by the overlap of a lot of orbitals. Add enough pi orbitals overlapping (which each hold a pair of electrons) and you get a band structure that happens to look a whole lot like the electronic structure of something like silicon (which can hold all the electrons you want.)

Charge transport, as in how charges actually move, is a lot more complicated; in general, we think that it involves well-ordered nano-scale regions which can hold one or more charges, separated by goopy amorphous grain boundaries which are barriers, more or less. Charge transport happens, among other methods, by the charges hopping from one grain to another via QUANTUM TUNNELLING, woo woo woo. This process is driven by an applied voltage that makes the charges "want" to move in one particular direction macroscopically, just like it does in any conductor or semiconductor (Ohm's law.)


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