TY  - JOUR
A1  - Tregnago, G
A1  - Wykes, M
A1  - Paterno, GM
A1  - Beljonne, D
A1  - Cacialli, F
JF  - Journal of Physical Chemistry C
UR  - http://dx.doi.org/10.1021/acs.jpcc.5b02345
SN  - 1932-7447
N2  - PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) is a highly soluble C60 derivative that is extensively used in organic solar cells, enabling power conversion efficiencies above 10%. Here we report, for the first time to the best of our knowledge, the photoluminescence of high-quality solvent-free PCBM crystals between room temperature and 4 K. Interestingly, the PL spectra of these crystals become increasingly structured as the temperature is lowered, with extremely well-resolved emission lines (and a minimum line width of ?1.3 meV at 1.73 eV). We are able to account for such a structured emission by means of a vibronic coupling model including Franck?Condon, Jahn?Teller and Herzberg?Teller effects. Although optical transitions are not formally forbidden from the low-lying excited states of PCBM, the high symmetry of the electronically active fullerene core limits the intensity of the 0?0 transition, such that Herzberg?Teller transitions which borrow intensity from higher-lying states represent a large part of the observed spectrum. Our simulations suggest that the emissive state of PCBM can be considered as a mixture of the T1g and Hg excited states of C60 and hence that the Hg state plays a larger role in the relaxed excited state of PCBM than in that of C60.
ID  - discovery1471747
IS  - 21
N1  - ACS AuthorChoice - This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
AV  - public
SP  - 11846
VL  - 119
Y1  - 2015/05/28/
EP  - 11851
TI  - Low-Temperature Photoluminescence Spectroscopy of Solvent-Free PCBM Single-Crystals
ER  -