I would like to get an answer in relation to exciton quenching in organic solar cells.
The reference: http://pubs.rsc.org/en/Content/ArticleLanding/2011/JM/C1JM12820E#!divAbstract
For a reliable answer to the question one will have to do a band-structure calculation. The experimental data shown in the Doc1.pdf file (regrettably the figure has no caption specifying the relevant details) seem to suggest that Au NPs introduce energy levels at band edges, and not like typical impurities inside the gap; impurities that introduce levels deep inside the gap generally give rise to reduction of peaks in the PL intensity (they give rise to exciton quenching, or non-radiative exciton recombination).
Dear benham,
Could you please more specific about metal nanoparticle concentration and PL intensity.
Dear Shamjid, PL intensity is a measure of the density of states. In the figure contained in the attached pdf file, one sees the PL intensity monotonically increasing for the concentration of gold nanoparticles increasing from 0% to 1.92% outside the double PEDOT:PSS layer (0.32% of gold nanoparticles in the latter region leaves the PL intensity corresponding to the case of 0% gold nonoparticles virtually unchanged). Importantly, the peak positions do not depend on the concentration of gold nanoparticles. These results could mean only one thing: that the gold nanoparticles do not introduce energy levels (localized states) inside the gap (for the concentrations considered), for if they did the PL intensities at the peak positions would only diminish, since mid-gap states would allow for non-radiative recombination of excitons; they seem only to increase the density of states in the energy regions where one already has considerable density of states in the case of 0% nonoparticles (recall that the peak positions prove to be independent of the concentration of gold nanoparticles; in all cases the PL intensity is describable in terms of two Lorentzians with constant peak positions, and increasing heights and increasing areas covered by them in the relevant frequency range).
@Benham,
'Importantly, the peak positions do not depend on the concentration of gold nanoparticles. ' then why PL increases with increase in concentration.
As I understood that, PL intensity inversely proportional to donnar/acceptor interface area. As PL increases D/A interface reduces and leading to decrease the exciton dissociation efficiency. so for higher concentration of NPs , PL higher lead to reduced exciton dissociation and device become less efficient. But how PL intensity varies with concentration of metal nanoparticles.
I thought you have given something related to this contest ,sorry I could understand.
Dear Shamjid, I was explicitly referring to the experimental data in file "Doc1.pdf" given below the question on this page (you may have noticed that in my first response on this page I point out lack of a caption specifying experimental details; for instance, the temperature is not given). These results indicate increase in the PL intensity with the increase in the concentration of gold nanoparticles. I explicitly mentioned the reason for this: increase in the density of states at the band edges. To appreciate this, the photons released in the photoluminescence process come about by the recombination of electrons and holes; when the peak positions do not depend on the concentration of gold nanoparticles, the conclusion can only be that energies of initial and final states do not change with changing this concentration; increase in the intensity further suggests increase in the number of relevant initial and final states (the are more electron-hole recombination events per unit time, thus increasing the intensity of photoluminescence).
Respect you benham....
Thanks a lot for your sincere approach .... I think you will help me as a good friend in the coming questions.... once again... thank you very much
You are welcome Shamjid. Incidentally, you may find the following excellent review by Timothy Gfroerer (published in Encyclopaedia of Analytic Chemistry, John Wiley & Sons, 2000) very useful:
http://www.phy.davidson.edu/FacHome/thg/Welcome_files/EAC-PL.pdf
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