18. August 2010
If interested, find it here (Reports on Progress in Physics 73, 096401 (2010)). Included: how do bulk heterojunctions and bilayers work, how to improve the performance, how to mass print, and a brief section on the cost. I am happy it is finally “on air”:) Free from IOP for the first 30 days, if you register. Otherwise, choose the arXiv version or drop me a line. As I am on vacation, expect some delay…
[Update 30.8.2010 ] Back from vacation for already a week: was very relaxing:) In order to avoid another “ad post”, I just extend this one a bit: the progress report on charge transfer complexes (accepted by Advanced Materials already in February) is now published online. You will not find this one on arXiv, so if you cannot access it, ask me to send you the preprint. As always, I am interested in your opinion and/or criticism!
Add to Connotea
Leave a Comment » | 
organic solar cells | Tagged: organic solar cells, physics | 
Permalink
Posted by deibel
3. August 2010
Adding to my selection of sayings (previously here, here and here 
Not always very deep, but mostly quite nice.
Jack London:
You can’t wait for inspiration. You have to go after it with a club.
William Gibson:
The future is here. It’s just not evenly distributed.
Niels Bohr:
I try never to write more clearly than I am able to think.
John von Neumann:
There is no sense in being precise when you don’t even know what you are talking about.
Henry Ford:
If I’d listened to customers, I’d have given them a faster horse.
Peter Drucker:
What everybody knows is frequently wrong.
Do not believe that it is very much of an advance to do the unnecessary three times as fast.
Add to Connotea
Leave a Comment » | off topic | Tagged: science&culture | Permalink
Posted by deibel
3. August 2010
Solarmer did it again: 8.13% power conversion efficiency, certified by NREL, were anounced at the currently running SPIE Optics and Photonics conference in San Diego.
I am also here, my talk will be on wednesday afternoon – but do not expect any breakthroughs in terms of performance from me:-) Maybe there will be more news here in the days to come.
In June and July, I was visiting scientist in the group of Mike McGehee at Stanford University for five very interesting weeks. Thanks again for hosting me, and for the interesting discussions we had! I also had a brief visit to PARC, the Palo Alto Research Center, for an interesting discussion with Robert Street about the photocurrent in organic solar cells. We finally agreed to disagree on some issues, but from my point of view, that’s absolutely fine.
During my Stanford visit, there was fortunately time enough for hiking in the Foothill Mountains as well! Highly recommended. Thanks to Andreas and Verena as well as Matthias for getting me started.
Read the rest of this entry »
Leave a Comment » | personal | Tagged: applications, organic solar cells, personal | Permalink
Posted by deibel
2. July 2010
Almost a year ago, I already discussed the photocurrent in organic bulk heterojunction solar cells. Also, recently I posted about the difficulties to determine the dominant loss mechanism from the short circuit current density dependence on the light intensity. 
Today, I would like to extend these statements to the photocurrent in somewhat more general terms.
The figure to the right contains the simulated photocurrent for a bulk heterojunction solar cell of 100nm thickness at room temperature. Parameters were chosen according to typical experimentally determined values for P3HT:PCBM solar cells: Bimolecular Langevin recombination with a reduction factor of 0.1 and electron and hole mobility of 10-4m2/Vs were assumed (is it possible I never discussed this reduction really? Seems so, just mentioned it with references here). The top graph shows the photocurrent, in the lower graph the photocurrent was divided by the illumination density in terms of suns (thus, the current densities given on the y-axis are only correct for 1 sun). Consequently, if the photocurrent scales linearly with the light intensity, all curves should coincide. Let me remind you that this was interpreted by different groups (Street et al. among them, but not the first to follow this explanation) as a sign of first order recombination.
Read the rest of this entry »
5 Comments | physics | Tagged: organic solar cells, physics | Permalink
Posted by deibel
6. May 2010
As promised, here a glimpse of why I believe that recombination in organic bulk heterojunction solar cells under short circuit conditions (and also at Voc) is not necessarily monomolecular.
Sometimes, the short circuit current density vs light intensity is measured, and from the linear scaling a dominant monomolecular recombination is concluded. In (partial) answer, we have performed some relevant device simulations (thanx to wapf). In short, we varied the generation of free charges over four orders of magnitude, assuming different polaron recombination mechanisms.
Read the rest of this entry »
18 Comments | organic solar cells | Tagged: organic solar cells, physics | Permalink
Posted by deibel
12. April 2010
Last week, the MRS Spring Meeting took place in San Francisco. It was my first time there, but certainly not the last! 
I enjoyed it immensely, despite my extensive last minute preparations of the talk I was invited to give… another first timer for me (on an international conference). In case you are interested, find the slides on scribd. Prof. Venkateswara Bommisetty, one of the organisers of the GG symposium told me that the slides of invited talks will also be made available (if the authors agree).
Many interesting talks, too many to go into more detail in the given time!;-) Anyway, it was nice to meet Alex (glidera) and his colleague Bertrand in person, and spend time with Andy B and Tom!
It was difficult (if not impossible) to agree with Alan Heeger and Robert Street on their propositions that monomolecular recombination is the limiting factor for organic bulk heterojunction solar cells at short circuit current under one sun illumination. Thus, despite both of them being well-known and highly respected, I allow myself to express my strong belief (supported by transient experiments and macroscopic simulations;-) that bimolecular polaron recombination is the dominant loss mechanism for free polarons, instead of monomolecular polaron recombination. Maybe more on this later.
During the conference, and featured in the talk of Karl Leo, Heliatek announced another efficiency record for small molecule solar cells, enhancing their recent achievements to now 7.7% certified efficiency for a tandem cell with 1.1cm2. Again, my congratulations, great stuff!
Read the rest of this entry »
4 Comments | science&culture | Tagged: organic solar cells, science&culture | Permalink
Posted by deibel
1. March 2010
I finished the Review article I was 
recently talking about. If you are interested, the preprint can be accessed here (in a few hours, 20:00 EST according to arXiv, so be patient;-) [Update 2nd March 2010] It’s up:-)
Reviews seem to be pretty subjective, and I am sure there are many omissions, but hopefully not too many inconsistencies. If there are any particular things you do like or do not like, or which are plain wrong: I am happy about every bit of constructive criticism! I submitted the article to Rep. Prog. Phys. It will be peer-reviewed, and I am pretty sure the referees’ comments will make the current version much less final as I’d like it to be;-)
[Update 25.6.2010] The review was accepted after some minor revisions, and is scheduled for publication by Rep. Prog. Phys. in September (2010).
Add to Connotea
2 Comments | organic solar cells | Tagged: organic solar cells, personal, physics | Permalink
Posted by deibel
24. February 2010
Via Die Zeit and Nature:
The DFG, Germany’s main funding agency, 
just put down new guidelines for proposals. Starting in July, the proposals should contain only two directly relevant publications per year of requested funding, as well as up to five other papers (presumably the most important ones) covering the researcher’s general background. Matthias Kleiner, DFG president:
It is quality, not quantity, which matters.
Good point. Nevertheless, although the publish and perish mentality lately became quite tiring, I wonder if (how quickly) these new conditions will change the mentality of the researchers in general, and in particular the ones who are reviewing the proposals and are sitting in the committees for professorship appointment;-)
[Update 25.2.2010] Find the original DFG statement here (pdf, german).
Add to Connotea
Leave a Comment » | science&culture | Tagged: science&culture | Permalink
Posted by deibel
