Electronic: QMMM in the complex TDDFT representation

Since the development of the first organic solar cell in 1983 with a power conversion efficiency lower than 1% [1] this area, also called plastic electronics, has grown and is growing today by leaps and bounds. From a power conversion efficiency of 2% in 2001 [2], we today reach efficiencies of over 8% [3], and BHJ solar cells with efficiencies approaching 10% are predicted [4].

Even if these recent development have been applied to concrete commercial applications, a lot of questions remain about the principle of functioning of those devices and about the photo-physical properties of conjugated materials. Consequently the full potential of those materials and devices has not been reached yet. One key question that needs to be answered is the relationship between the morphology of one phase and its absorption properties.
We focus here on the case of the C70(PCBM) system, which has been used together with a low band gap polymer (TQ1) that has a donor phase [5].

Molecular dynamics simulations are performed at a finite temperature, from which snapshots are selected. From these, absorption spectra are computed using QM/MM complex response theory and averaged to create the final absorption spectrum.

1 – Chamberlain, G. A. Sol. Cells, 1983, 8, 47
2 – Shaheen, S. E.; Brabec, C. J.; Saricifti, N. S. Appl. Phys. Lett., 2001, 78, 841
3 – Green, M. A.; Emery, K.; Hishikawa, Y. ; Warta, W.; Dunlop, E. D. Prog. Photovolt., 2010, 19, 565
4 – Brabec, C. J., Gowrisanker, S., Halls, J. J. M., Laird, D., Jia, S., and Williams, S. P. Adv. Mater., 2010, 22, 3839
5 – Wang, E. G.; Hou, L. T.; Wang, Z. Q.; Hellstrom, S.; Zhang, F. L.; Inganäs, O.; Andersson, M.R. Adv. Mater., 2010 , 22 , 5240-5244