## Interaction of light with solids in experiment and simulation

2. February 2015

Hi there, sorry for not getting back to you but starting a new group and having new responsibilities (e.g. involvement in new degree programmes for Material Science) can take (part of) the blame. Just as brief progress indicator, here a link to an interview of the Chemnitz University of Technology press office with me. (Photo: Uwe Meinhold)

The official short name of my group is OPKM, for Optics and Photonics of Condensed Matter. For the (very) long official name I refer you to the web page of the Institute of Physics at the TUC;-) The size of my group is growing slowly but steadily, and the lab building shows progress as well: setups for time correlated single photon counting to measure photoluminescence transients – e.g. to determine charge carrier recombination in perovskite solar cells – and for confocal measurements of luminescence are already available from my predecessor’s group: we just adapt them to our needs. Other setups, time resolved and steady state, are being built and come along nicely. Solar cell preparation is still improvised, using the glovebox system of a colleague and the evaporation chamber of another, until we get our own integrated glovebox/evaporator system. One of my main interests is still Organic Photovoltaics, and with my (PhD) background in inorganic photovoltaics I also look at the hybrid perovskite solar cell hype (as a hype is not necessarily a bad thing;-). What also remains is my joy to combine experiments and simulations (macroscopic device simulations, kinetic Monte Carlo simulations) to understand these systems.

If you are interested in joining us: I have two PhD positions available at present. Please check out the job offer (german; computer-translated here) and contact me.

Cheers!

## Restarting in Chemnitz

20. March 2014

Just a brief note, I moved from Würzburg to the Institute of Physics at Chemnitz University of Technology this March, starting a new group. At present I have one PhD position open on Organic Photovoltaics – funded by the University, therefore including some teaching duty in German. Have a look here (in German) or drop me a line if you are interested. Cheers,

Carsten

25. August 2013

Some links I found interesting since the last time… partly older stuff, though.

## Nongeminate recombination in organic solar cells – slower than expected

21. August 2013

In a “recent” post (just 3 posts but 10 months ago;-) I wrote once again on the derivation of the Langevin recombination rate for nongeminate recombination. The question is, is Langevin recombination really what governs the charge carrier loss rate in organic solar cells?

Recombination of electrons with holes is usually a 2nd order decay. As electrons $n$ and holes $p$ are photogenerated pair wise, the respective excess charge carrier concentrations are symmetric, $n=p$. Then a recombination rate $R$ is

$R = k n p = k n^2$,

where the recombination prefactor $k$ could be a Langevin prefactor – more on that later. In a transient experiment with a photogenerating, short laser pulse at $t=0$, the continuity equation for charge carriers (here, e.g. electrons) under open circuti conditions (no external current flow, for instance if the experiment is done on a thin film without electrodes)

$\frac{dn}{dt} = G-R$

becomes

$\frac{dn}{dt} = -R$

for $t>0$ (as the generation was only at $t=0$).

If all electrons and hole are available for recombination (i.e., can reach all other charge carriers and can be reached by them), then the recombination rate and the continuity equation for $t>0$ yield

$\frac{dn}{dt} = k n^2$ Read the rest of this entry »

## New life – again

18. March 2013

On 11th of February (my birthday, incidentally), our 2nd child was born: Nicolas Jacob. We are so happy, as is our 2 year old daughter Chiara.

Even with only one kid, it was already rather quiet on this blog in the last months (well, 2 years…). Still, I do have some hope to be able to dedicate one or the other quiet minute to write some urgently needed updates to previous posts. All the best, Carsten

## Belectric aquires German Konarka Daughter

23. October 2012

Related to this post on Konarka’s bankruptcy: According to a range of news sites, including pv-tech.org, the german company Belectric has acquired Konarka Technologies. Find the press release here (pdf).

The system integrator Belectric is situated in Lower Franconia, less than 50km from Würzburg and less than 10km from where I live. Let’s keep our fingers crossed!

## Nongeminate Recombination: Langevin (again) and beyond (later;-)

16. October 2012
Nongeminate recombination is the major loss mechanism for state-of-the-art organic solar cells. In an early blog post, I showed how the Langevin recombination was derived. Although there is more to nongeminate recombination than just this mechanism, it is still instructive and also relevant to trap-assisted recombination mechanisms, due to its mobility-containing prefactor.

[Nenashev 2010] pointed out that in the derivation of the Langevin recombination,

since the electric field scales as r−2 and the surface area of the sphere scales as 2, the value of r chosen is unimportant, leading to a simple solution with constant electron den- sity, thus justifying the neglect of diffusion.