Ambipolar transport

Zaumseil J, Sirringhaus H (2007) Electron and ambipolar transport in organic field-effect transistors. Chem Rev 107 1296-1323... 

Saudari SR, Frail PR, Kagan CR (2009) Ambipolar transport in solution-deposited pentacene transistors enhanced by molecular engineering of device contacts. Appl Phys Lett 95 023301... 

Saudari SR, Lin Y-J, Lai Y, Kagan CR (2010) Device configurations for ambipolar transport in flexible pentacene transistors. Adv Mater 44 5063-5068... 

Langmuir-Blodgett (LB) technique has been also used for the preparation of Pc-based OFET, as it allows the fine control of both the structure and the thickness of the film at the molecular level [226,227], OFET devices based on amphiphilic tris(phthalocyaninato) rare earth, triple-decker complexes have been prepared by LB technique, showing good OFET performances [228], More recently, ambipolar transport has also been realized in OFET devices through a combination of holeconducting CuPc and n-conducting Cgo fullerene, in which the asymmetry of the... 

Fig. 5.11. Comparison of the unipolar and ambipolar transport characteristics of a p-type semiconductor (MDMO-PPV) based diode at different temperatures...

Formally, it will be even necessary to make corrections already in the starting flux equations. The detailed formulation of linear irreversible thermodynamics also includes coupling terms (cross terms) obeying the Onsager reciprocity relation. They take into account that the flux of a defect k may also depend on the gradient of the electrochemical potential of other defects. This concept has been worked out, in particular, for the case of the ambipolar transport of ions and electrons.230... 

Depending on the details of the carrier distributions and densities, majority and minority carrier parameters have different importance. Under ambipolar transport conditions, which often hold in solar cell operation, the ambipolar urproduct is the relevant transport parameter. This has a somewhat complicated dependence on the minority- and majority-carrier parameters, but in many cases it can be approximated by the minority-carrier uz product. However, when the absorber material is not sufficiently doped, or if the absorber layer is depleted, a distinction between minority and majority carriers becomes difficult, and a more in-depth analysis may be needed, as discussed by Bube (1992). 

In this work we have chosen the combination of hole-conducting copper-phthalocyanine (CuPc) and the n-conducting fullerene C o, which are both known from organic photovoltaic cells either as heterolayer structures or bulk-heterojunctions [18-21]. They can be considered as model systems for ambipolar transport where the asymmetry of the electron and hole mobilities is adjustable by the concentration of both materials in the mixture. 

The change from p- to n-conduction was already observed following the first step of fluorination, from PcZn to p4PcZn. If ambipolar transport in phthalocyanines is aimed at, unsubstituted phthalocyanines seem to be the best choice [47] since hole conduction could not be achieved for any of the presently stud-... 

Zaumseil, J., Friend, R., and Sirringhaus, H., Spatial control of the recombination zone in an ambipolar light-emitting organic transistor, Nat. Mater., 5, 69, 2006. Chesterfield, R. J. et al.. High electron mobility and ambipolar transport in organic thin-fibn transistors based on a Jt-stacking quinoidal terthiophene, Adv. Mater., 15, 1278, 2003. 

FIGURE 2.3.5 Transfer characteristics of bottom-gate OC,C,q PPV and P3HT FET with trap-free BCB gate dielectric exhibiting clean ambipolar transport (V = 60V). (Courtesy of Jana Zaumseil, University of Cambridge.)... 

Chesterfield, R.J. et al.. High electron mobility and ambipolar transport in organic thin-... 

Quaterthiophenes High Mobility N-Channel Semiconductors and Ambipolar Transport, J. Am. Chem. Soc. 127 (5), 1348-1349, 2005. 

Th B. Singh, S. Gunes, N. Marjanovic, N. S. Sariciftci, and R. Menon. Correlation between morphology and ambipolar transport in organic field-effect transistors. Journal of Applied Physics, 97(ll) 114508-5, 2005. 

By assuming that the transport number for oxygen ions is zero (cf. Eq. (1.32)), the only flux of hydrogen remaining is that of ambipolar transport of protons and electrons ... 

This is a good point at which to look a little closer at the ambipolar transport term that we have mentioned eartier in passing. The materials property of interest here is the protonic-electronic ambipolar conductivity term, which can be written in... 

We note that the molecular flux is proportional to the difference in hydrogen pressure (as in gas phase transport through a piorous membrane), whereas atomic transport has a square root dependence, and as such would behave similarly to ambipolar transport of protons and electrons limited by the conductivity of a minority concentration of protons. 

Ambipolar Transport in Conjugated Organic Polymers and Transistors... 

This chapter concentrates on organic bipolar transistors, including details about the basic operation principles, device configurations, and processing methods, and describing the various strategies that have been applied to achieve ambipolar transport. Touching upon small molecule-based FETs and the hybrid approach, the main focus will be on polymer-based bipolar transistors since they can provide one of the ultimate solutions for simple, low-cost fabrication of flexible bipolar FETs. 

R. J. Chesterfield, C. R. Newman, T. M. Pappenfus, P. C. Ewbank, M. H. Haukaas, K. R. Maim, L. L. Miller and C. D. Frisbie, High electron mobility and ambipolar transport in organic thin-film transistors based on a a-stacking quinoidal terthiophene, Adv. Mater, 15, 1278-1282 (2(X)3). 

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