TY - JOUR A1 - Castellani, Mauro A1 - Salzmann, Ingo A1 - Bugnon, Philippe A1 - Yu, Shuwen A1 - Oehzelt, Martin A1 - Koch, Norbert T1 - Structural and electronic implications for carrier injection into organic semiconductors N2 - We report on the structural and electronic interface formation between ITO (indium-tin-oxide) and prototypical organic small molecular semiconductors, i.e., CuPc (copper phthalocyanine) and alpha-NPD (N,N'-di(naphtalen-1-yl)- N,N'-diphenyl-benzidine). In particular, the effects of in situ oxygen plasma pretreatment of the ITO surface on interface properties are examined in detail: Organic layer-thickness dependent Kelvin probe measurements revealed a good alignment of the ITO work function and the highest occupied electronic level of the organic material in all samples. In contrast, the electrical properties of hole-only and bipolar organic diodes depend strongly on the treatment of ITO prior to organic deposition. This dependence is more pronounced for diodes made of polycrystalline CuPc than for those of amorphous alpha-NPD layers. X-ray diffraction and atomic force microscopic (AFM) investigations of CuPc nucleation and growth evidenced a more pronounced texture of the polycrystalline film structure on the ITO substrate that was oxygen plasma treated prior to organic layer deposition. These findings suggest that the anisotropic electrical properties of CuPc crystallites, and their orientation with respect to the substrate, strongly affect the charge carrier injection and transport properties at the anode interface. Y1 - 2009 UR - http://www.springerlink.com/content/100501 U6 - https://doi.org/10.1007/s00339-009-5336-6 SN - 0947-8396 ER - TY - JOUR A1 - Lu, Guanghao A1 - Blakesley, James C. A1 - Himmelberger, Scott A1 - Pingel, Patrick A1 - Frisch, Johannes A1 - Lieberwirth, Ingo A1 - Salzmann, Ingo A1 - Oehzelt, Martin A1 - Di Pietro, Riccardo A1 - Salleo, Alberto A1 - Koch, Norbert A1 - Neher, Dieter T1 - Moderate doping leads to high performance of semiconductor/insulator polymer blend transistors JF - Nature Communications N2 - Polymer transistors are being intensively developed for next-generation flexible electronics. Blends comprising a small amount of semiconducting polymer mixed into an insulating polymer matrix have simultaneously shown superior performance and environmental stability in organic field-effect transistors compared with the neat semiconductor. Here we show that such blends actually perform very poorly in the undoped state, and that mobility and on/off ratio are improved dramatically upon moderate doping. Structural investigations show that these blend layers feature nanometre-scale semiconductor domains and a vertical composition gradient. This particular morphology enables a quasi three-dimensional spatial distribution of semiconductor pathways within the insulating matrix, in which charge accumulation and depletion via a gate bias is substantially different from neat semiconductor, and where high on-current and low off-current are simultaneously realized in the stable doped state. Adding only 5 wt% of a semiconducting polymer to a polystyrene matrix, we realized an environmentally stable inverter with gain up to 60. Y1 - 2013 U6 - https://doi.org/10.1038/ncomms2587 SN - 2041-1723 VL - 4 IS - 1-2 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Salzmann, Ingo A1 - Heimel, Georg A1 - Duhm, Steffen A1 - Oehzelt, Martin A1 - Pingel, Patrick A1 - George, Benjamin M. A1 - Schnegg, Alexander A1 - Lips, Klaus A1 - Blum, Ralf-Peter A1 - Vollmer, Antje A1 - Koch, Norbert T1 - Intermolecular hybridization governs molecular electrical doping JF - Physical review letters N2 - Current models for molecular electrical doping of organic semiconductors are found to be at odds with other well-established concepts in that field, like polaron formation. Addressing these inconsistencies for prototypical systems, we present experimental and theoretical evidence for intermolecular hybridization of organic semiconductor and dopant frontier molecular orbitals. Common doping-related observations are attributed to this phenomenon, and controlling the degree of hybridization emerges as a strategy for overcoming the present limitations in the yield of doping-induced charge carriers. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevLett.108.035502 SN - 0031-9007 VL - 108 IS - 3 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Ghani, Fatemeh A1 - Opitz, Andreas A1 - Pingel, Patrick A1 - Heimel, Georg A1 - Salzmann, Ingo A1 - Frisch, Johannes A1 - Neher, Dieter A1 - Tsami, Argiri A1 - Scherf, Ullrich A1 - Koch, Norbert T1 - Charge Transfer in and Conductivity of Molecularly Doped Thiophene-Based Copolymers JF - Journal of polymer science : B, Polymer physics N2 - The electrical conductivity of organic semiconductors can be enhanced by orders of magnitude via doping with strong molecular electron acceptors or donors. Ground-state integer charge transfer and charge-transfer complex formation between organic semiconductors and molecular dopants have been suggested as the microscopic mechanisms causing these profound changes in electrical materials properties. Here, we study charge-transfer interactions between the common molecular p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane and a systematic series of thiophene-based copolymers by a combination of spectroscopic techniques and electrical measurements. Subtle variations in chemical structure are seen to significantly impact the nature of the charge-transfer species and the efficiency of the doping process, underlining the need for a more detailed understanding of the microscopic doping mechanism in organic semiconductors to reliably guide targeted chemical design. KW - charge transfer KW - conducting polymers KW - doping KW - thiophene Y1 - 2015 U6 - https://doi.org/10.1002/polb.23631 SN - 0887-6266 SN - 1099-0488 VL - 53 IS - 1 SP - 58 EP - 63 PB - Wiley-Blackwell CY - Hoboken ER -