Category: organic solar cells

Hot CT complexes and Geminate Recombination

Lately, the notion that geminate recombination in organic solar cells is a major loss mechanism is more and more under fire. Foothill MountainsStreet et al present an “experimental test” for geminate recombination [Street 2010a]. They investigate P3HT:PC60BM nor PCDTBT:PC70BM bulkheterojunction solar cells with a transient current technique at 200K and 300K between -1 and 1V external voltage bias. The authors conclude that neither exhibit significant geminate recombination, while pointing out that

Since the relative importance of geminate or nongeminate recombination depends on the specific materials comprising the cell and possibly on the method of preparation, other cells may or may not have a larger geminate recombination contribution.

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Brief Ad: Organic Solar Cell Review Online [Update]

Sunset in UmbriaIf 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 (submitted to 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!

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Type of Polaron Recombination under Short Circuit Conditions [Update]

Eagle (?) in the EvergladesAs 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.

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Be aware of ads…

I finished the Review article I was Schlumpf1recently 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).

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Towards ten percent… Solarmer hits 7.9% with plastic solar cell

Via pv-tech. Brief note on efficiency record: Solarmer has managed to get an (NREL certified) power conversion efficiency of 7.9% for an organic solar cell… sounds good, and broke the recent record (by the same company). It is important to mention, though, that the active area was very small with 0.1cm2 (aperture 0.047cm2).

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Funding for Organic Photovoltaics Company

Many people believe that organic photovoltaics companies will have to prove soon that Fliegenpilz im Herbstwald (no direct connection between photo and blog content are implied;-)they can come up with commercially viable products within the next two-three years. In this context, Heliatek, a Germany based company developing organic small molecule solar cells with high efficiency, has received 18 Million Euros in a second round of funding from venture capitalists and others. From the press release:

Heliatek will be utilizing the new funding primarily to build an initial production facility in Dresden. In this step and right through to mass production, the company will be using its proprietary tandem technology to efficiently produce, flexible and very lightweight PV modules on a film substrate. Their weight will be merely 500 grams per square meter, instead of today’s customary 20 kilograms per square meter. This will open up a forward-looking market for mobile applications, for architectural solutions and for independently supplying regions with weak infrastructures.

Indeed, interesting times for OPV – particularly in view of the commercial aspects! The science aspects are also getting more and more interesting, but unfortunately I thus have less and less time to write about them here…

P.S. Another company Solexant just starts the production of hybrid solar cells after the process developed by the group of Paul Alivisatos at Berkeley, as reported by Technology Review.

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