Limits...
Role of redox centre in charge transport investigated by novel self-assembled conjugated polymer molecular junctions.

Wang Z, Dong H, Li T, Hviid R, Zou Y, Wei Z, Fu X, Wang E, Zhen Y, Nørgaard K, Laursen BW, Hu W - Nat Commun (2015)

Bottom Line: Molecular electronics describes a field that seeks to implement electronic components made of molecular building blocks.To date, few studies have used conjugated polymers in molecular junctions despite the fact that they potentially transport charge more efficiently than the extensively investigated small-molecular systems.More significantly, we decorate redox-active functionality into polymeric backbones, demonstrating a key role of redox centre in the modulation of charge transport behaviour via energy level engineering and external stimuli, and implying the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.

ABSTRACT
Molecular electronics describes a field that seeks to implement electronic components made of molecular building blocks. To date, few studies have used conjugated polymers in molecular junctions despite the fact that they potentially transport charge more efficiently than the extensively investigated small-molecular systems. Here we report a novel type of molecular tunnelling junction exploring the use of conjugated polymers, which are self-assembled into ultrathin films in a distinguishable 'planar' manner from the traditional vertically oriented small-molecule monolayers. Electrical measurements on the junctions reveal molecular-specific characteristics of the polymeric molecules in comparison with less conjugated small molecules. More significantly, we decorate redox-active functionality into polymeric backbones, demonstrating a key role of redox centre in the modulation of charge transport behaviour via energy level engineering and external stimuli, and implying the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.

No MeSH data available.


Related in: MedlinePlus

Modulation of TTF–PPE junctions via chemical oxidation.I–V characteristics of (a) PPE and (b) TTF–PPE junctions before/as-prepared (black square) and after treated with excess iron perchlorate hexahydrate (red circle). The plots are generated from average values obtained from least 20 junctions of the same batch. Insets of a and b show statistics on sheet resistance of the PPE and TTF–PPE junctions, respectively. (c) Fowler–Nordheim plot for I–V traces of TTF2+–PPE junctions. Inset shows the energy level diagram of TTF2+–PPE/Au.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4557373&req=5

f5: Modulation of TTF–PPE junctions via chemical oxidation.I–V characteristics of (a) PPE and (b) TTF–PPE junctions before/as-prepared (black square) and after treated with excess iron perchlorate hexahydrate (red circle). The plots are generated from average values obtained from least 20 junctions of the same batch. Insets of a and b show statistics on sheet resistance of the PPE and TTF–PPE junctions, respectively. (c) Fowler–Nordheim plot for I–V traces of TTF2+–PPE junctions. Inset shows the energy level diagram of TTF2+–PPE/Au.

Mentions: The electronic properties of CP films before and after chemical oxidation were measured using the above-mentioned rGO top-contact test bed. The sheet resistance of PPE and TTF–PPE junctions (inset of Fig. 5a,b) is calculated from low-bias regimes (−0.1 V≤V≤0.1 V) of I(V) characteristics. Experimental evidences confirmed that a modulation of conductance of TTF–PPE junctions was achieved via oxidant treatment on the CP films, which was not observed for non-redox-active PPE junctions. The Rs of TTF2+–PPE junction was on average one order of magnitude higher than that of their neutral state (Fig. 5b). F–N plots indicated Vtrans at 0.37±0.08 V (Fig. 5c), ∼0.1 V larger than that observed before oxidation. UPS revealed a much larger barrier for hole injection after the oxidant treatment (up to 1.04 eV compared with 0.76 eV, Fig. 5c; inset). In addition, from the absorption spectra (Fig. 4b), the energy gap was enlarged via oxidation (from 2.30 to 2.51 eV). No characteristic changes on conductance of PPE junctions were recorded on oxidant treatment, confirming that the modulating effect is originated from the redox changes of TTF unit. The active role of redox centre in the modulation of device performance also further confirms the contribution from polymeric backbones dominates the charge transport process, agreeing well with previous discussions. A summary of energy levels and Vtrans for CPs and small molecules in this work is shown in Table 1.


Role of redox centre in charge transport investigated by novel self-assembled conjugated polymer molecular junctions.

Wang Z, Dong H, Li T, Hviid R, Zou Y, Wei Z, Fu X, Wang E, Zhen Y, Nørgaard K, Laursen BW, Hu W - Nat Commun (2015)

Modulation of TTF–PPE junctions via chemical oxidation.I–V characteristics of (a) PPE and (b) TTF–PPE junctions before/as-prepared (black square) and after treated with excess iron perchlorate hexahydrate (red circle). The plots are generated from average values obtained from least 20 junctions of the same batch. Insets of a and b show statistics on sheet resistance of the PPE and TTF–PPE junctions, respectively. (c) Fowler–Nordheim plot for I–V traces of TTF2+–PPE junctions. Inset shows the energy level diagram of TTF2+–PPE/Au.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4557373&req=5

f5: Modulation of TTF–PPE junctions via chemical oxidation.I–V characteristics of (a) PPE and (b) TTF–PPE junctions before/as-prepared (black square) and after treated with excess iron perchlorate hexahydrate (red circle). The plots are generated from average values obtained from least 20 junctions of the same batch. Insets of a and b show statistics on sheet resistance of the PPE and TTF–PPE junctions, respectively. (c) Fowler–Nordheim plot for I–V traces of TTF2+–PPE junctions. Inset shows the energy level diagram of TTF2+–PPE/Au.
Mentions: The electronic properties of CP films before and after chemical oxidation were measured using the above-mentioned rGO top-contact test bed. The sheet resistance of PPE and TTF–PPE junctions (inset of Fig. 5a,b) is calculated from low-bias regimes (−0.1 V≤V≤0.1 V) of I(V) characteristics. Experimental evidences confirmed that a modulation of conductance of TTF–PPE junctions was achieved via oxidant treatment on the CP films, which was not observed for non-redox-active PPE junctions. The Rs of TTF2+–PPE junction was on average one order of magnitude higher than that of their neutral state (Fig. 5b). F–N plots indicated Vtrans at 0.37±0.08 V (Fig. 5c), ∼0.1 V larger than that observed before oxidation. UPS revealed a much larger barrier for hole injection after the oxidant treatment (up to 1.04 eV compared with 0.76 eV, Fig. 5c; inset). In addition, from the absorption spectra (Fig. 4b), the energy gap was enlarged via oxidation (from 2.30 to 2.51 eV). No characteristic changes on conductance of PPE junctions were recorded on oxidant treatment, confirming that the modulating effect is originated from the redox changes of TTF unit. The active role of redox centre in the modulation of device performance also further confirms the contribution from polymeric backbones dominates the charge transport process, agreeing well with previous discussions. A summary of energy levels and Vtrans for CPs and small molecules in this work is shown in Table 1.

Bottom Line: Molecular electronics describes a field that seeks to implement electronic components made of molecular building blocks.To date, few studies have used conjugated polymers in molecular junctions despite the fact that they potentially transport charge more efficiently than the extensively investigated small-molecular systems.More significantly, we decorate redox-active functionality into polymeric backbones, demonstrating a key role of redox centre in the modulation of charge transport behaviour via energy level engineering and external stimuli, and implying the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.

ABSTRACT
Molecular electronics describes a field that seeks to implement electronic components made of molecular building blocks. To date, few studies have used conjugated polymers in molecular junctions despite the fact that they potentially transport charge more efficiently than the extensively investigated small-molecular systems. Here we report a novel type of molecular tunnelling junction exploring the use of conjugated polymers, which are self-assembled into ultrathin films in a distinguishable 'planar' manner from the traditional vertically oriented small-molecule monolayers. Electrical measurements on the junctions reveal molecular-specific characteristics of the polymeric molecules in comparison with less conjugated small molecules. More significantly, we decorate redox-active functionality into polymeric backbones, demonstrating a key role of redox centre in the modulation of charge transport behaviour via energy level engineering and external stimuli, and implying the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.

No MeSH data available.


Related in: MedlinePlus