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One strategy to improve the photovoltaic properties of nonfullerene acceptors (NFAs), employed in state-of-art organic solar cells, is the rational fluorination or chlorination of these molecules. Although this modification improves important acceptor properties, little is known about the effects on the triplet states. Here, we combine the polarizable continuum model with an optimally tuned range-separated hybrid functional to investigate this issue. We find that fluorination or chlorination of NFAs decreases the degree of the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) overlap along these molecules. Consequently, the energy gap between T

The solar spectrum matching of the low bandgap polythiophenes is attractive for device applications in photoelectric energy conversion. Polythiophenes can be chemically synthesized as soluble polymers, or deposited by electrochemical methods. They also can present higher mobility values, which is important for improving the efficiency of photovoltaic devices. The use of polythiophenes in combination with bulkminsterfullerene C60 is promising; the photo-induced electron transfer from the excited state of a conducting polymer onto C60 opened the possibility of constructing efficient photovoltaic devices with new approach for the development of plastic photodetectors and solar cells. As a single polymer layer device presents low efficiency due to the mechanism of charge generation and transport, the use of a C60 molecule, which has high electron affinity value, sublimed onto the polymer in a heterojunction (bilayer) or mixed in the polymer film (blend) increased drastically the efficiency of the photovoltaic devices. In this chapter, photovoltaic devices based on several polythiophene derivatives in combination with C60 and its derivatives will be discussed. Electrical, optical, and morphological studies in bilayers or blend active layers will be presented. The photoelectric conversion enhancement was achieved (i) by means of energy transfer between polymers in a blend active layer and (ii) by improving absorption in the active layers by light trapping.

Tin oxide (TO) or fluorine doped tin oxide (FTO) has been frequently used as a transparent electrode in our organic opto-electronic devices [1-3]. In general, these devices are fabricated in a sandwich structure where an organic thin layer (approx. 100nm thick) stays between two conducting electrodes, TO or FTO and Al. Due to higher conductivity FTO is normally our choice. The morphology of the electrodes influences the morphology of the organic layer, mainly when the deposition of the organic layer is done electrochemically.

2,3-Dihydro-2-(4'-hydroxyphenyl)-3-methyl-5(E)-propenylbenzofuran (conocarpan) (1), 2-(4'-hydroxy-3'-methoxyphenyl)-3-methyl-5(E)- propenylbenzofuran (eupomatenoid-5) (2), and 2-(4'- hydroxyphenyl)-3-methyl-5(E)-propenylbenzofuran (eupomatenoid-6) (3), three known neolignans found for the first time in a species of the Piperaceae, were isolated from Piper decurrens via insecticidal bioassay-guided fractionation, along with a small quantity of a new related compound, 2,3-dihydro-5-formyl-2-(4'-hydroxyphenyl)-3-methylbenzofuran (decurrenal) (4), and 3,7,11,15-tetramethyl-2(E)-hexadecen-1-ol (trans-phytol).