Comments on: Polaron, Polaron Pair, Exciton, Exciplex, …

By: deibel

deibel — Thu, 22 Dec 2011 11:32:15 +0000

I never cared much for solitons, sorry. Have you checked the book by Pope/Swenberg? C

By: ashwininmallya

ashwininmallya — Thu, 22 Dec 2011 11:05:40 +0000

Hi, my question is regarding solitons.Can polyaniline have solitons as charge carriers?Is it correct that only conducting polymers like polyacetylene can have solitons as charge carriers?

By: Células Solares Orgánicas « Meditaciones Dactilares

Células Solares Orgánicas « Meditaciones Dactilares — Thu, 04 Aug 2011 10:31:55 +0000

[...] es la “blend” (o tener los dos tipos de polímero mezclados entre si(. En el siguiente enlace está muy bien explicado la formación y la disociación de estos [...]

By: deibel

deibel — Tue, 12 Jul 2011 15:20:25 +0000

Your question is not clear to me, sorry.

By: bin

bin — Tue, 12 Jul 2011 15:15:30 +0000

Hi, Dr. Deibel , thanks a lot for your post. I am a graduate student, have a question about polarons. Does polaron or polaron pairs have the temperature dependence？

By: deibel

deibel — Fri, 11 Feb 2011 08:07:31 +0000

Hi Kejia, thanks for your question: it is a good one, and would deserve a post, but I'll try to give ou a starting point. Singlet and triplet generation upon injection is more relevant for charge injection based devices such as organic light emitting diodes. These are made of a single organic semiconductor, not a blend. Thus, the lowest excited states are "normal" excitons, not charge transfer excitons (or polaron pairs) across a donor-acceptor heterojunction. As the spins of the two exciton constituents can each be up or down, four configurations are possible - one singlet and three triplets. If spin statistics work, you will have a 25% chance of forming a singlet exciton upon injection an electron and an (uncorrelated) hole into the organic semiconductor. (If the chance can be increased beyond 25% is an important question for the quantum efficiency of OLEDs; interesting albeit older reviews are [Yersin 2004] and [Wohlgenannt 2003], also including the detailed mechanisms). For solar cells, the optical excitation is more important: optically, usually only singlet excitons (for instance on the donor material) are generated, which can become triplets directly only by intersystem crossing. The latter can be on a picosecond time scale, but is still slower than the fs electron transfer, and thus less favourable. Another triplet generation mechanism is electron back transfer, which can occur after successful electron transfer if the charges do not find enough transport paths to get away from the interface (and if the process is energetically possible). For some further reading, see [Veldman 2009].

By: Kejia Li

Kejia Li — Wed, 09 Feb 2011 04:24:51 +0000

Hi Dr. Deibel,

Thank you so much for posting so many important terms in your blog, which is really helpful.

I have a question to ask here about the excitons generation due to charge injection. In this page, as well as in your paper (Rep. Prog. Phys. 73 (2010) 096401), you mentioned “Singlet and triplet excitons can also be formed due to interaction following charge injection”. I’m really curious about how this process happens, because it’s very important to understand the carrier transport at equilibrium and steady state.

Thank you so much and look forward to your reply.

Kejia

By: ineverwantedtobeascientistiwantedtobealumberjack

ineverwantedtobeascientistiwantedtobealumberjack — Sun, 09 Jan 2011 10:41:16 +0000

We do need some definition for terms, and the description you offer here is a good start but I dont know if i would describe them exactly as you do here. Firstly your description of an exciplex is not great; an exciplex is an excited state complex between two different chromophores. By definition the excited state is shared by the two chromophores. If the two chromophores are the same you get an excimer (excited state dimer). You also dont differentiate between chromophores and molecules. Also there is a problem with what is the actual difference between your definition of an exciton (a bound electron hole pair) and a polaron pair (a bound electron hole pair). For me, possibly the easiest definition of the difference is that in an exciton , hole and electron effect their surroundings as a unit, i.e. they relax as a unit. In a polaron pair , there are two polarons which relax individually into their surroundings, but due to their proximity apply coulombic interaction on each other. But this is only what i think. As a community we definitely need agreed upon definitions and we need them soon.

By: jekaliho

jekaliho — Sat, 08 May 2010 20:25:23 +0000

Hi Carsten, thanks so much for your prompt and full reply! It has helped me to think about the range of states possible and what they physically mean. Best wishes, Jenna.

By: deibel

deibel — Tue, 27 Apr 2010 16:57:22 +0000

Hi Jenna, thanks for your kind comment! Concerning your question, I have added a hopefully helpful update at the end of the post. Best, Carsten

By: jekaliho

jekaliho — Sun, 25 Apr 2010 16:59:49 +0000

Hello,

Firstly, thank you for your blog! I’m finding it very useful as I’ve just started a PhD in organic solar cells.

I have a question on exciton-types. Hopefully you might be able to shed some light on my confusion. I’m looking at systems in which Frenkel and Charge-Transfer exctions have been found but I’m trying to get my head round exactly what a CT exciton is. In my (maybe simplified view) it was simply an exciton created when the electron from one material (e.g. polymer) was promoted to (close to) the LUMO level of another material (e.g. fullerene). The article below mentions them but in context of CT states being filled by Frenkel excitons.

With regards to your diagram would the CT exciton be equivalent to the polaron pair? I presumed it wasn’t or else they’d call it a polaron! It is definitely something shared between materials and no on one molecule so it isn’t an exciplex. Can the polaron pair be generated directly by light absorption?

http://www3.interscience.wiley.com/cgi-bin/fulltext/122630062/PDFSTART

If you can clarify this at all I’ll be very grateful!

Jenna