A new semiconducting polymer, PDPP3T, with alternating diketopyrrolopyrrole and terthiophene units is presented. PDPP3T has a small band gap of 1.3 eV and exhibits nearly balanced hole and electron ...mobilities of 0.04 and 0.01 cm2 V−1 s−1, respectively, in field-effect transistors (FETs). By the combination of two identical ambipolar transistors, an inverter was constructed that exhibits a gain of ∼30. When PDPP3T was combined with 60PCBM or 70PCBM in a 1:2 weight ratio, photovoltaic cells were made that provide a photoresponse up to 900 nm and an AM1.5 power conversion efficiency of 3.8 or 4.7%, respectively. In contrast to the almost constant FET mobility, the efficiency of the photovoltaic cells was found to be strongly dependent on the molecular weight of PDPP3T and the use of diiodooctane as a processing agent.
A new easily accessible, high molecular weight, alternating dithieno‐diketopyrrolopyrrolophenylene copolymer provides high electron and hole mobilities exceeding 0.02 cm2 V−1 s−1 in FETs and AM1.5 ...power conversion efficiencies of 4.6% and 5.5% in solar cells when combined with 60PCBM and 70PCBM. The performance of the solar cells strongly depends on the use of a processing agent.
Gelatins are proteinaceous natural materials that are widely used in areas such as conservation and restoration of artifacts as adhesives and consolidants, in pharmaceutics as drug delivery carriers, ...and in the food industry as structurants. Herein, type A porcine gelatin adhesive films are prepared via solution casting method and their physical and mechanical properties are investigated using X‐ray diffraction (XRD), differential scanning calorimetry, contact angle measurement, dynamic mechanical analysis, and uniaxial tensile tests. The results demonstrate a linear correlation between microstructure of gelatin films in terms of their triple‐helix content and their macroscopic mechanical properties such as tensile strength and gel (Bloom) strength. Moreover, the findings of this study can help the scientists, in, e.g., art conservation and restoration, to predict the mechanical performance of these adhesives by performing a less material demanding and nondestructive physical measurement such as XRD.
Gelatins are proteinaceous materials widely used in the conservation of artworks, pharmaceutics as drug delivery carriers, and the food industry as structurants. Herein, the results demonstrate how the molecular level structural features dictate macroscopic mechanical behavior of gelatin films. Moreover, physical techniques such as X‐ray diffraction and differential scanning calorimetry can be used to predict the macroscopic mechanical properties of gelatin films.
Alternating copolymers based on cyclopentadithiophene (CPDT) and five different electron‐deficient aromatic units with reduced optical band gaps are synthesized via Suzuki coupling. All polymers show ...a significant photovoltaic response when mixed with a fullerene acceptor. The frontier orbital levels of the new polymers are designed to minimize energy losses by increasing the open‐circuit voltage with respect to the optical band gap, while maintaining a high coverage of the absorption with the solar spectrum. The best cells are obtained for a copolymer of CPDT and benzooxadiazole (BO) with a band gap of 1.47 eV. This cell gives a short‐circuit current of 5.4 mA cm−2, an open‐circuit voltage of 0.78 V, and a fill factor of 0.6, resulting in a power conversion efficiency of about 2.5%.
Optimization of the energy levels of alternating CPDT‐X copolymers is achieved by varying the electron‐deficient aromatic segment and results in materials that feature minimal energy losses in bulk‐heterojunction solar cells. For PCPDT‐BO:PCBM, the offset between the band gap and open‐circuit voltage cell is only ∼0.7 eV. This low offset contributes to its high power conversion efficiency (2.5%).
In the search of new electron acceptor, n‐type materials for organic solar cells that combine a strong absorption over a broad range with good electrical characteristics, the use of ...diketopyrrolopyrrole (DPP) derivatives with low reduction potentials is explored. A series of small molecule DPP derivatives is presented and the compounds are tested as electron acceptors in combination with poly(3‐hexylthiophene) (P3HT) as the donor material. Working photovoltaic devices are obtained that show a photoresponse in the wavelength region where the DPP molecules absorb. The best device shows a power conversion efficiency of 0.31% in simulated solar light, with a photon‐to‐electron conversion efficiency of ∼10% up to 700 nm. The efficiency seems to be limited by the coarse morphology of the blend.
Diketopyrrolopyrroles (DPPs) are explored in the search of new electron acceptor materials for organic solar cells. DPPs have already been successfully used as donor materials, but also have low reduction potentials and significant electron mobilities. A series of small DPP molecules is presented and the compounds are tested as electron acceptors, in combination with polythiophene as a donor, in organic solar cells. The best device shows an efficiency of 0.31%.
In this work, we propose the use of regular branching of polyurethanes as a way to regulate chain dynamics and govern crystallization in highly dense hydrogen-bonded systems. As a result, robust and ...healable polyurethanes can be obtained. To this end, we synthesized a range of aliphatic propane diol derivatives with alkyl branches ranging from butyl (C4) to octadecanyl (C18). The series of brush polyurethanes was synthesized by polyaddition of the diols and hexamethylene diisocyanate. Polyurethanes with very short (C < 4) and very long (C = 18) brush lengths did not lead to any significant healing due to crystallization. An intermediate amorphous regime appears for polymers with middle branch lengths (C = 4 to 8) showing a fine control of material toughness. For these systems, the side chain length regulates tube dilation, and significant macroscopic healing of cut samples was observed and studied in detail using melt rheology and tensile testing. Despite the high healing degrees observed immediately after repair, it was found that samples with medium to long length brushes lost their interfacial strength at the healed site after being heated to the healing temperature for some time after the optimal time to reach full healing. Dedicated testing suggests that annealed samples, while keeping initial tackiness, are not able to completely heal the cut interface. We attribute such behavior to annealing-induced interfacial crystallization promoted by the aliphatic branches. Interestingly, no such loss of healing due to annealing was observed for samples synthesized with C4 and C7 diols, which is identified as the optimal healing regime. These results point at the positive effect of branching on healing, provided that a critical chain length is not surpassed, as well as the need to study healing behavior long after the optimal healing times.
A series of polythiophenes (PT
n) based on dialkyl-cyclopentadithiophene (CPDT) units alternating with short un-substituted thiophene segments of length
n (
n being the number of thiophenes) along ...the chain has been synthesized to control the morphology of PT
n:PCBM blends for solar cell applications via the chemical structure of the polymer rather than via (post) processing conditions. The degree of phase separation in PT
n:PCBM blends can be controlled via
n, because with increase in
n the number of solublizing side chains per thiophene is reduced. For the most soluble derivative, PT0, we find that PCBM crystallizes first, while for the least soluble version, PT3, polymer aggregation prevails. The most intimately mixed morphology and best solar cells were obtained for PT2, which exhibits a power conversion efficiency (PCE) of about 1.5% under AM1.5G conditions when mixed with PCBM. Although the final PCE is moderate, the study represents an example of a rational approach towards morphology control via chemical structure, rather than via processing.
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