TTA as a potential hole transport layer for application in conventional polymer solar cells

Hole transport layers(HTLs)play a vital role in organic solar cells(OSCs).In this work,a derivative of tetrathiafulvalene with four carboxyl groups TTA was introduced as a novel HTL to fabricate OSC with high performance.Displaying a better energy level match between HTL and active layers,the TTA based devices show a peak power conversion efficiency of 9.09%,which is comparable to the devices based on PEDOT:PSS.The favorable surface morphology recorded via atomic force microscopy,low series loss and charge recombination indicated by electrochemical impedance spectroscopy,synchronously verify the potential of TTA for application in OSCs as a valid kind of HTLs.

Hydrogen bonding networks controllable by the substitution position of tetrathiafulvalene on the pyridine ring

Tetrathiafulvalene(TTF), as a classical building unit, has attracted considerable attention, especially its functional derivatives. Hydrogen bonding(H-bonding) networks are a class of traditional and stable nanostructures, which play an important role in two-dimensional self-assembly and multi-component co-assembly. In this paper, we studied the regulation of H-bonding networks by functional groups in TTF derivatives. The results indicate that the position of pyridine on TTF not only affects their self-assembly structures in different solvents, but also controls the H-bonding networks through different mechanisms. Both para-TTF and meta-TTF molecules show different co-assembled structures with solvents depending on whether or not the presence of carboxylic acid group. On the pre-prepared H-bonding networks formed by famous 1,3,5-tris(10-carboxydecyloxy)-benzene(TCDB) molecule, both para-TTF and meta-TTF disturbed the original network structures with different degree of TCDB deformation. The formed new H-bonding networks with or without TTF derivatives participation are mainly attributed to the position of pyridine in TTF-based molecules. These results would be important for design of exceptional and functional nanostructures starting with the design of building block.

Self-assemblies of TTF derivatives with fluorinated phenyls and pyridine group

The self-assembly characteristics of tetrathiafulvalene(TTF) derivatives molecules 1-3 at the 1-phenyloctane/HOPG(HOPG = highly oriented pyrolytic graphite) interface had been carefully studied by scanning tunneling microscopy(STM) method. The number of F atoms on the phenyl group had significantly affected the self-assembly structures. High-resolution STM images make clear the different assembly structures between the molecules 1-3, which attribute to the different F atom numbers and pyridine group in the molecule. Density functional theory(DFT) calculations have been performed to reveal the formation mechanism.

Sequence modulation of tunneling barrier and charge transport across histidine doped oligo-alanine molecular junctions

Series tunneling across peptides composed of various amino acids is one of the main charge transport mechanisms for realizing the function of protein. Histidine, more frequently found in redox active proteins, has been proved to be efficient tunneling mediator. While how it exactly modulates charge transport in a long peptide sequence remains poorly explored. In this work, we studied charge transport of a model peptide junction, where oligo-alanine peptide was doped by histidine at different position,and the series of peptides were self-assembled into a monolayer on gold electrode with soft EGa In as top electrode to form molecular junction. It was found that histidine increased the overall conductance of the peptide, meanwhile, its position modulated the conductance as well. Quantitative analysis by transport model and ultraviolet photoelectron spectroscopy(UPS) indicated a sequence dependent energy landscape of the tunneling barrier of the junction. Density-functional theory(DFT) calculation on the electronic structure of histidine doped oligo-alanine peptides revealed localized highest occupied molecular orbital(HOMO) on imidazole group of the histidine, which decreased charge transport barrier.