Abstract
In this work, a series of eight thiophene-based polymers (exploited as “donors” in bulk heterojunction photovoltaics cells), whose structures were designed to be suitably tuned with the electronic characteristics of the [6,6]-Phenyl C61 butyric acid methyl ester (PCBM), is considered,. The electronic properties of the mono-, di-, trimeric oligomers are reckoned (at the Hartree-Fock and DFT level of the theory) and compared to experimental spectroscopic and electrochemical results. Indeed, electrochemical and spectroscopic results show a systematic difference whose physical nature is assessed and related to the exciton (electron-hole) binding energy (). The critical comparison of the experimental and theoretical band gaps, i.e., the HOMO-LUMO energy difference, suggests that electrochemical and DFT values are the most suited to being used in the design of a polythiophene-based p-n junction for photovoltaics.
Highlights
The electronic properties of eight thiophene-based polymers (Figure 1 shows the relevant structures), with a particular focus on the interfacial behavior, are rationalized within a “Lego-like sum approach”: the electronic properties of the mono, di, trimeric species are calculated, and eventually the trimer results are selected and shown, in the following figures, to represent the electronic features of the polymer system well
Periodic boundaryperiodic condition (PBC) calculations were calculations performed, the latter results the latter results well compare with the band gap relevant to the dimeric and trimeric well compare with the HOMO-LUMO band gap relevant to the dimeric and trimeric species, together species, with the systematic of with the together systematic calculationdi, of TDDFT
(optical band gap, calculated latter are obtained (i) by means of spectroscopical measurements, ∆EOPT, and (ii) by means of Cyclic voltammetry (CV)
Summary
The electronic properties of eight thiophene-based polymers (Figure 1 shows the relevant structures), with a particular focus on the interfacial behavior, are rationalized within a “Lego-like sum approach”: the electronic properties of the mono-, di-, trimeric species are calculated, and eventually the trimer results are selected (the differences between the dimer and trimer oligomers are almost negligible) and shown, in the following figures, to represent the electronic features of the polymer system well. Such a general modelistic approach spans extremely different worlds: from the. [21,22]
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