## Photocurrent again

I covered the photocurrent already before, for instance here. I pointed out that from the light intensity dependence of the short circuit current, it is impossible for many typical conditions to unambiguously determine the dominant loss mechanism or even the recombination order (1st (often called monomolecular, but not my favourite term;-) or 2nd order of decay).

If, however, you know (or guess) that the recombination order is two, you can use the above mentioned $j_{sc}$ vs. $P_L$ data to determine which fraction of charges is lost to bimolecular recombination, $\eta_{br}$. This was shown recently by [Koster 2011]. For $j_{sc} \propto P_L^\alpha$, they found $\eta_{br} = \alpha^{-1}-1$. Although I was not able to follow the exact derivation ([Update 5.4.2011] it can be derived by solving a simple differential equation, $\alpha=(1-dR/dG)/(1-R/G)=(1-\eta_{br}')/(1-\eta_{br})$), it seems to work. Easy method, although make sure not to have too much space charge in your device – even at the contacts, induced by low (ohmic) injection barriers (we compared it to our device simulation, and then you get significant deviations)! In my opinion, the latter point is not stressed enough in the paper, despite the nice approach. Continue reading “Photocurrent again”