TY - JOUR A1 - Albrecht, Steve A1 - Janietz, Silvia A1 - Schindler, Wolfram A1 - Frisch, Johannes A1 - Kurpiers, Jona A1 - Kniepert, Juliane A1 - Inal, Sahika A1 - Pingel, Patrick A1 - Fostiropoulos, Konstantinos A1 - Koch, Norbert A1 - Neher, Dieter T1 - Fluorinated Copolymer PCPDTBT with enhanced open-circuit voltage and reduced recombination for highly efficient polymer solar cells JF - Journal of the American Chemical Society N2 - A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC70BM compared to the well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer HOMO level, resulting in high open-circuit voltages well exceeding 0.7 V. Optical spectroscopy and morphological studies with energy-resolved transmission electron microscopy reveal that the fluorinated polymer aggregates more strongly in pristine and blended layers, with a smaller amount of additives needed to achieve optimum device performance. Time-delayed collection field and charge extraction by linearly increasing voltage are used to gain insight into the effect of fluorination on the field dependence of free charge-carrier generation and recombination. F-PCPDTBT is shown to exhibit a significantly weaker field dependence of free charge-carrier generation combined with an overall larger amount of free charges, meaning that geminate recombination is greatly reduced. Additionally, a 3-fold reduction in non-geminate recombination is measured compared to optimized PCPDTBT blends. As a consequence of reduced non-geminate recombination, the performance of optimized blends of fluorinated PCPDTBT with PC70BM is largely determined by the field dependence of free-carrier generation, and this field dependence is considerably weaker compared to that of blends comprising the non-fluorinated polymer. For these optimized blends, a short-circuit current of 14 mA/cm(2), an open-circuit voltage of 0.74 V, and a fill factor of 58% are achieved, giving a highest energy conversion efficiency of 6.16%. The superior device performance and the low band-gap render this new polymer highly promising for the construction of efficient polymer-based tandem solar cells. Y1 - 2012 U6 - https://doi.org/10.1021/ja305039j SN - 0002-7863 VL - 134 IS - 36 SP - 14932 EP - 14944 PB - American Chemical Society CY - Washington 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 -