Polyfluorene homopolymer (P1) and its carbazole derivatives (P2–P4) have been prepared with good yield by Suzuki coupling polymerization. P2 is an alternating copolymer based on fluorene and carbazole; P3 is a hyperbranched polymer with carbazole derivative as the core and polyfluorene as the long arms; P4 is a hyperbranched polymer with carbazole derivative as the core and the alternating fluorene and carbazole as the long arms. These polymers show highly thermal stability, and their structures and physical properties are studied using gel permeation chromatography, 1H NMR, 13C NMR, elemental analysis, Fourier transform infrared spectroscopy, thermogravimetry, UV–vis absorption, photoluminescence, and cyclic voltammetry (CV). The influence of the incorporation of carbazole and the hyperbranched structures on the thermal, electrochemical, and electroluminescent properties has been investigated. Both carbazole addition and the hyperbranched structure increase the thermal and photoluminescent stability. The CV shows an increase of the HOMO energy levels for the derivatives, compared with polyfluorene homopolymer (P1). The EL devices fabricated by these polymers exhibit pure blue‐light‐emitting with negligible low‐energy emission bands, indicating that the hyperbranched structure has a strong effect on the PLED characteristics. The results imply that incorporating carbazole into polyfluorene to form a hyperbranched structure is an efficient way to obtain highly stable blue‐light‐emitting conjugated polymers, and it is possible to adjust the property of light‐emitting polymers by the amount of carbazole derivative incorporated into the polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 790–802, 2008

Excitation migration dynamics and the energy-transfer process in a donor−acceptor pair system on photoexcitation have been investigated by using static and time-resolved photoluminescence (PL) measurements. The PL spectrum of poly(N-vinylcarbazole) (PVK) was fully superposed on the electronic absorption spectrum of poly(9,9‘-di-n-hexyl-2,7-fluorenylvinylene) (PDHFV) to fulfill a requirement for an efficient Förster-type energy transfer. In the PL spectrum of a blended PVK film with 0.5 wt % PDHFV on photoexcitation at 340 nm, the PL emission of PDHFV, which exhibits little absorbance at the excitation wavelength, prevailed over the PL emission of PVK. The PL spectrum of a bilayered structure with a PVK layer thickness of 4 μm and a PDHFV layer thickness of 80 nm, which was prepared by spin-casting PDHFV solution in trichloroethylene on a PVK film, also showed the PL emission of PDHFV on photoexcitation of the PVK layer at 340 nm without a trace of the PL emission of PVK. Excitation energy migration through a PVK bulk was observed up to a PVK thickness of 23 μm. A time-correlated single-photon counting (TCSPC) study deduced an energy migration velocity of 3.5 × 106 cm/s and a dwell time between each hopping of 85 fs, respectively, in the PVK bulk of the bilayered structures with a PDHFV layer thickness of 10 or 80 nm.

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Thiophene-pyrazine-thiophene building blocks with carboxamide or carbamate substituents were synthesized and their crystal structures were compared. The carboxamide substituted building block formed intermolecular hydrogen bonds. It showed twisted conformations and...

The damp‐heat (DH) degradation of silicon heterojunction (SHJ) solar modules leads to severe power loss, necessitating superior‐quality encapsulation materials. Herein, it is aimed to investigate the mechanical, thermal, and optical properties of ethylene vinyl acetate (EVA), polyolefin elastomer (POE), and thermoplastic polyolefin (TPO). TPO demonstrates the lowest water vapor transmission rate (WVTR) of only 3.14 g (m2·day)−1, which is approximately seven times lower than that of EVA. The Fourier transform infrared spectroscopy of EVA demonstrates a loss of the carbonyl group, revealing the formation of acetic acid under DH stress, which is not observed in POE and TPO. Both glass/back sheet and glass/glass (G/G) modules show a significant influence of encapsulant material on DH degradation. The maximum output power (Pmax) of the G/TPO/G single‐cell module maintains 96.6% of its initial value after 1000 h DH stress. After sealing the edge, the G/G commercial‐size modules encapsulated with lower WVTR encapsulants display excellent DH reliability, and Pmax degrades <4.8% after 3000 h of DH stress. The predicted levelized cost of energy (LCOE) decreases ≈0.11 US cents/(KW h), which boosts additional power generation and illustrates the remarkable potential for the SHJ solar modules meeting the requirements of reliable, sustainable, and low‐LCOE systems.