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Air-stable dimers of sandwich compounds including rhodocene and (pentamethylcyclopentadienyl)(arene)ruthenium and iron derivatives can be used for n-doping electron-transport materials with electron affinities as small as 2.8 eV. A p-i-n homojunction diode based on copper phthalocyanine and using rhodocene dimer as n-dopant shows a rectification ratio of greater than 10(6) at 4 V.

Molecular doping is a powerful method to fine-tune the thermoelectric properties of organic semiconductors, in particular to impart the requisite electrical conductivity. The incorporation of molecular dopants can, however, perturb the microstructure of semicrystalline organic semiconductors, which complicates the development of a detailed understanding of structure-property relationships. To better understand how the doping pathway and the resulting dopant counterion influence the thermoelectric performance and transport properties, a new dimer dopant, (N-DMBI) 2 , is developed. Subsequently, FBDPPV is then n-doped with dimer dopants (N-DMBI) 2 , (RuCp*mes) 2 , and the hydride-donor dopant N-DMBI-H. By comparing the UV-vis-NIR absorption spectra and morphological characteristics of the doped polymers, it is found that not only the doping mechanism, but also the shape of the counterion strongly influence the thermoelectric properties and transport characteristics. (N-DMBI) 2 , which is a direct electron-donating dopant with a comparatively small, relatively planar counterion, gives the best power factor among the three systems studied here. Additionally, temperature-dependent conductivity and Seebeck coefficient measurements differ between the three dopants with (N-DMBI) 2 yielding the best thermoelectric properties.

CVD graphene has been n-and p-doped using redox-active, solutionprocessed metal-organic complexes. Electrical measurements, photoemission spectroscopies, and Raman spectroscopy were used to characterise the doped films and give insights into the changes.The work function decreased by as much as 1.3 eV with the n-dopant, with contributions from electron transfer and surface dipole, and the conductivity significantly increased.

Solution-based n-doping of the polymer poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} [P(NDI2OD-T2)] and the small molecule 6,13-bis(tri(isopropyl)silylethynyl)pentacene (TIPS-pentacene) is realized with the air-stable dimers of rhodocene, [RhCp2]2, and ruthenium(pentamethylcyclopentdienyl)(1,3,5-triethylbenzene), [Cp*Ru(TEB)]2. Fermi level shifts, measured by direct and inverse photoemission spectroscopy, and orders of magnitude increase in current density and film conductivity point to strong n-doping in both materials. The strong reducing power of these air-stable dopants is demonstrated through the n-doping of TIPS-pentacene, a material with low electron affinity (3.0 eV). Doping-induced reduction of the hopping transport activation energy indicates that the increase in film conductivity is due in part to the filling of deep gap states by carriers released by the dopants.

2197 www.MaterialsViews.com wileyonlinelibrary.comcan be straightforwardly controlled down to a few nanometers by co-evaporation of the host and the dopant molecules. [ 2,4,12,13 ] Carrier injection enhancement of several orders-of-magnitude in organic lightemitting diodes and transistors has been demonstrated. [14][15][16][17][18] Doping-induced enhancement of charge carrier collection at small-molecule organic solar cell contacts has also been demonstrated. [ 12,13,19 ] Achieving the same degree of spatial control of dopant profi le for polymerbased devices is more challenging: polymer fi lms are solution-deposited and, although doped fi lms can be obtained via deposition of a solution containing the host and dopant, spatial distribution of the dopants cannot be easily controlled. Sequential spin-coating of undoped and doped fi lms using orthogonal solvents is one possible approach; however, the polymer-solvent compatibility needed for forming high quality fi lms and interfaces is not assured. We present here a conceptually simple approach based on soft-contact transferlamination (SCTL) of a polymer homojunction, using a soft stamp, for example, polydimethylsiloxane (PDMS), as a transfer medium. SCTL has been extensively used in the past for the deposition of metal electrodes [ 20,21 ] or active layers in organic transistors [ 22,23 ] and photovoltaic cells. [24][25][26][27][28] In the present case, two polymer fi lms, one undoped and one doped, are prepared separately via spin-coating, and then joined via SCTL to realize doped hole-injection or -collection contacts for diodes and solar cells. We have previously demonstrated with two polymers, poly(3-hexylthiophene) (P3HT) ( Figure 1 ) and poly[(9-,9-dioctylfl uorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′-3}-thiadiazole)] (F8BT), that the lamination process of undoped fi lms leads to "transparent" homojunctions, that is, interfaces that are electronically and electrically seamless [ 29 ] as evidenced by the facts that i) no signifi cant energy shift of molecular levels occurs across the SCTL junction, and ii) the current injected from either electrode is independent of whether the middle layer consists of a single polymer fi lm of thickness "t", or of two laminated fi lms with the same total thickness "t' . These results demonstrate that SCTL is a viable method for assembling multilayer polymer devices from separately fabricated layers, thus enabling functionalization, doping, and other materials modifi cation of specifi c parts of a device structure. Though demonstrated to work effectively across metal-metal interfaces, this Poly(3-hexylthiophene) (P3HT) is p-doped by the new soluble dopant molybdenum tris[1-(methoxycarbonyl)-2-(trifl uoromethyl)-ethane-1,2-dithiolene] and investigated via photoemission spectroscopy and transport measurements.Soft-contact transfer lamination of thin layers of the doped P3HT on undoped polymer layers is used to create spatially-confi ned doped regions, which serve as hole-injection contacts on P3HT diodes. This strategy is then used to...

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