Abstract
The variation of the HOMO-LUMO band gap is explored for varying packing arrangements of the 4mod BT-4TIC donor-acceptor molecule pair, by means of a high-throughput ab-initio random structure search of packing possibilities. 350 arrangements of the dimer have been relaxed from initial random dispositions, using non-local density-functional theory. We find that the electronic band gap varies within 0.3 eV, and that this magnitude, the binding energy, and the geometry are not significantly correlated. A clearly favoured structure is found with a binding energy of 1.75±0.07 eV, with all but three other arrangements displaying values of less than one third of this highest binding one, which involves the aliphatic chain of 4TIC.
Highlights
The need to find renewable and environmentally friendly energy sources alternative to the traditional fossil fuels is nowadays a global quest
The absorption of the solar photons in the donor-acceptor mixture gives rise to electron-hole pairs which spontaneously separate into charge carriers, the latter being collected by charge-selective electrodes thereby generating electric power
One of the most important and used magnitudes in organic solar cells (OSCs) is the difference between the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor, which is commonly known as the HOMO-LUMO band gap, or gap hereafter
Summary
The need to find renewable and environmentally friendly energy sources alternative to the traditional fossil fuels is nowadays a global quest. The solar energy is a promising candidate and solution-processed organic solar cells (OSCs) have attracted attention because of their low cost, light weight, mechanical flexibility, and potential application in large-area devices [1,2,3]. A typical OSC is formed by mixed donor and acceptor molecules placed between two electrodes. The absorption of the solar photons in the donor-acceptor mixture gives rise to electron-hole pairs which spontaneously separate into charge carriers, the latter being collected by charge-selective electrodes thereby generating electric power.
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