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Synthesis, structure, and opto-electronic properties of organic-based nanoscale heterojunctions.

Rezek B, Cermák J, Kromka A, Ledinský M, Hubík P, Mareš JJ, Purkrt A, Cimrová V, Fejfar A, Kočka J - Nanoscale Res Lett (2011)

Bottom Line: We show that employing and combining advanced scanning probe techniques can provide us significant insight into the correlation of these properties.These data are further correlated with local material composition detected using micro-Raman spectroscopy and with other electronic transport data.We demonstrate benefits of this multi-dimensional characterizations on (i) bulk heterojunction of fully organic composite films, indicating differences in blend quality and component segregation leading to local shunts of photovoltaic cell, and (ii) thin-film heterojunction of polypyrrole (PPy) electropolymerized on hydrogen-terminated diamond, indicating covalent bonding and transfer of charge carriers from PPy to diamond.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Physics ASCR, v,v,i,, Cukrovarnická 10, 16200 Prague 6, Czech Republic. rezek@fzu.cz.

ABSTRACT
Enormous research effort has been put into optimizing organic-based opto-electronic systems for efficient generation of free charge carriers. This optimization is mainly due to typically high dissociation energy (0.1-1 eV) and short diffusion length (10 nm) of excitons in organic materials. Inherently, interplay of microscopic structural, chemical, and opto-electronic properties plays crucial role. We show that employing and combining advanced scanning probe techniques can provide us significant insight into the correlation of these properties. By adjusting parameters of contact- and tapping-mode atomic force microscopy (AFM), we perform morphologic and mechanical characterizations (nanoshaving) of organic layers, measure their electrical conductivity by current-sensing AFM, and deduce work functions and surface photovoltage (SPV) effects by Kelvin force microscopy using high spatial resolution. These data are further correlated with local material composition detected using micro-Raman spectroscopy and with other electronic transport data. We demonstrate benefits of this multi-dimensional characterizations on (i) bulk heterojunction of fully organic composite films, indicating differences in blend quality and component segregation leading to local shunts of photovoltaic cell, and (ii) thin-film heterojunction of polypyrrole (PPy) electropolymerized on hydrogen-terminated diamond, indicating covalent bonding and transfer of charge carriers from PPy to diamond.

No MeSH data available.


Related in: MedlinePlus

Hall effect measurements on PPy-diamond heterojunctions. (a) Schematic top view of the diamond in-plane mesa structure for Hall effect measurements showing a bare H-terminated mesa structure and its transformation into PPy-diamond mesa structure. Mesa surroundings are electrically insulated by oxidation of diamond surface. The resin encapsulation is used to confine PPy growth to the mesa area. (b) Hall voltage on the PPy-diamond mesa structure measured under +0.3 T (triangles) and - 0.3 T (squares) as a function of time. (c) The same Hall voltage plotted as a function of magnetic field. All measurements were done under the cold light illumination.
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Figure 10: Hall effect measurements on PPy-diamond heterojunctions. (a) Schematic top view of the diamond in-plane mesa structure for Hall effect measurements showing a bare H-terminated mesa structure and its transformation into PPy-diamond mesa structure. Mesa surroundings are electrically insulated by oxidation of diamond surface. The resin encapsulation is used to confine PPy growth to the mesa area. (b) Hall voltage on the PPy-diamond mesa structure measured under +0.3 T (triangles) and - 0.3 T (squares) as a function of time. (c) The same Hall voltage plotted as a function of magnetic field. All measurements were done under the cold light illumination.

Mentions: To reduce the effect of Hall voltage drift, we re-designed electrical connection of the PPy-diamond structure as shown in Figure 10a and also increased the magnetic field. The obtained diagonal Hall voltage under white light illumination (cold light source, 40 klx) is plotted as a function of time in Figure 10b. The Hall voltage is still varying in time, and the difference between values for positive and negative magnetic field, which should correspond to the true Hall voltage, is decreasing. We assign this effect to temperature gradients (up to several kelvins) arising in the measuring chamber because of heat flow from the magnet coils. These gradients create thermal and thermomagnetic electromotoric forces (EMFs) [55] of the order of 1 mV modifying the measured voltage. In more conductive samples, these EMFs can be partially suppressed by alternating the direction of the measuring current. Unfortunately, in our case, the necessary long times of RC relaxation and integration (tens of minutes) prevent a successful application of this procedure. However, after leaving the magnet to cool down to room temperature, the repeated measurement shows a similar dependence, confirming in this way that we really observed the Hall voltage.


Synthesis, structure, and opto-electronic properties of organic-based nanoscale heterojunctions.

Rezek B, Cermák J, Kromka A, Ledinský M, Hubík P, Mareš JJ, Purkrt A, Cimrová V, Fejfar A, Kočka J - Nanoscale Res Lett (2011)

Hall effect measurements on PPy-diamond heterojunctions. (a) Schematic top view of the diamond in-plane mesa structure for Hall effect measurements showing a bare H-terminated mesa structure and its transformation into PPy-diamond mesa structure. Mesa surroundings are electrically insulated by oxidation of diamond surface. The resin encapsulation is used to confine PPy growth to the mesa area. (b) Hall voltage on the PPy-diamond mesa structure measured under +0.3 T (triangles) and - 0.3 T (squares) as a function of time. (c) The same Hall voltage plotted as a function of magnetic field. All measurements were done under the cold light illumination.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211298&req=5

Figure 10: Hall effect measurements on PPy-diamond heterojunctions. (a) Schematic top view of the diamond in-plane mesa structure for Hall effect measurements showing a bare H-terminated mesa structure and its transformation into PPy-diamond mesa structure. Mesa surroundings are electrically insulated by oxidation of diamond surface. The resin encapsulation is used to confine PPy growth to the mesa area. (b) Hall voltage on the PPy-diamond mesa structure measured under +0.3 T (triangles) and - 0.3 T (squares) as a function of time. (c) The same Hall voltage plotted as a function of magnetic field. All measurements were done under the cold light illumination.
Mentions: To reduce the effect of Hall voltage drift, we re-designed electrical connection of the PPy-diamond structure as shown in Figure 10a and also increased the magnetic field. The obtained diagonal Hall voltage under white light illumination (cold light source, 40 klx) is plotted as a function of time in Figure 10b. The Hall voltage is still varying in time, and the difference between values for positive and negative magnetic field, which should correspond to the true Hall voltage, is decreasing. We assign this effect to temperature gradients (up to several kelvins) arising in the measuring chamber because of heat flow from the magnet coils. These gradients create thermal and thermomagnetic electromotoric forces (EMFs) [55] of the order of 1 mV modifying the measured voltage. In more conductive samples, these EMFs can be partially suppressed by alternating the direction of the measuring current. Unfortunately, in our case, the necessary long times of RC relaxation and integration (tens of minutes) prevent a successful application of this procedure. However, after leaving the magnet to cool down to room temperature, the repeated measurement shows a similar dependence, confirming in this way that we really observed the Hall voltage.

Bottom Line: We show that employing and combining advanced scanning probe techniques can provide us significant insight into the correlation of these properties.These data are further correlated with local material composition detected using micro-Raman spectroscopy and with other electronic transport data.We demonstrate benefits of this multi-dimensional characterizations on (i) bulk heterojunction of fully organic composite films, indicating differences in blend quality and component segregation leading to local shunts of photovoltaic cell, and (ii) thin-film heterojunction of polypyrrole (PPy) electropolymerized on hydrogen-terminated diamond, indicating covalent bonding and transfer of charge carriers from PPy to diamond.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Physics ASCR, v,v,i,, Cukrovarnická 10, 16200 Prague 6, Czech Republic. rezek@fzu.cz.

ABSTRACT
Enormous research effort has been put into optimizing organic-based opto-electronic systems for efficient generation of free charge carriers. This optimization is mainly due to typically high dissociation energy (0.1-1 eV) and short diffusion length (10 nm) of excitons in organic materials. Inherently, interplay of microscopic structural, chemical, and opto-electronic properties plays crucial role. We show that employing and combining advanced scanning probe techniques can provide us significant insight into the correlation of these properties. By adjusting parameters of contact- and tapping-mode atomic force microscopy (AFM), we perform morphologic and mechanical characterizations (nanoshaving) of organic layers, measure their electrical conductivity by current-sensing AFM, and deduce work functions and surface photovoltage (SPV) effects by Kelvin force microscopy using high spatial resolution. These data are further correlated with local material composition detected using micro-Raman spectroscopy and with other electronic transport data. We demonstrate benefits of this multi-dimensional characterizations on (i) bulk heterojunction of fully organic composite films, indicating differences in blend quality and component segregation leading to local shunts of photovoltaic cell, and (ii) thin-film heterojunction of polypyrrole (PPy) electropolymerized on hydrogen-terminated diamond, indicating covalent bonding and transfer of charge carriers from PPy to diamond.

No MeSH data available.


Related in: MedlinePlus