We report the conjugated polymer P(tBu-CBP) as a host with high triplet energy (E(T) 2.53 eV) and suitable HOMO (5.3 eV) and LUMO (2.04 eV) energy levels. Upon doping with green and red emission Ir-complexes, it gives devices with high luminous and external quantum efficiencies for green emission (23.7 cd/A, 6.57%) and for red emission (5.1 cd/A, 4.23%), respectively, and low turn-on voltage (3 V). For both devices, the efficiencies are higher than those of the corresponding devices with the same backbone P(3,6-Cz) as a host by a factor of 4, even though the latter has an E(T) (2.6 eV) slightly higher than that of the former. The results reflect that, in phosphorescent devices, the difference in E(T) between the host and guest is not the only factor that determines the device efficiency, and the present side group modification via the 9 position of carbazole also plays an important role, which allows a tuning of HOMO and LUMO levels to provide more balance in electron and hole fluxes and provides prevention from formation of excimer.

occupied molecular orbital (HOMO) level of the polymer, which has a direct impact on the V OC of the cell. In addition, it is important to achieve low-bandgap PSCs with great stability for the purpose of practical applications. While thermal stability of PSCs is related to thermal properties of the polymer, air stability can be affected by the HOMO level of the polymer. Polymers with deeper HOMO levels are generally more stable against the oxidation by air. Lastly, high-performance low-bandgap polymers should also exhibit high charge transport ability in order to achieve high fi ll factors (FF). [ 24,25 ] Among the reported low bandgap polymers, diketopyrrolopyrrole (DPP) has been a commonly used building block due to its excellent properties such as strong absorption covering near-infrared and visible regions, its electron defi cient nature and high charge carrier mobility. A polymer (DT-PDPP2T-TT) has been reported as the best low-bandgap polymer, which could achieve an impressive short-circuit current density ( J sc) of 20.07 mA cm −2 with diphenolether as additive. The open circuit voltage ( V OC ) of cell is still relatively low (0.67 V) due to the relatively electron-rich nature of thienothiophene-based donor unit. [ 13 ] Another high-performance low-bandgap polymer is C3-DPPTT-T (with a high effi ciency up to 8.8%), which offers an excellent J sc up to 23.5 mA cm −2 but still exhibits a V OC of 0.57 V. [ 17 ] To increase the V OC of DPP-based low bandgap polymers, an effective strategy is to copolymerize the DPP unit with donor building blocks that are less electron-rich than thiophene or thienothiophene. When a benzodithiophene unit was copolymerized with DPP, a signifi cantly higher V OC of 0.73 V was achieved, but the cell effi ciency was signifi cantly lower (6.6% for single junction cell). [ 10 ] Recently, a DPP-based D 1 -A-D 2 -Atype low bandgap polymer (PDPP3T alt TPT) was reported with the introduction of a phenyl ring between two DPP2T moieties. This polymer further increases the V OC to 0.75 V and can achieve an excellent PCE of 8.0%. [ 16 ] In this paper, we report a novel DPP polymer (named poly(difluorobenzothiadiazole-bisthiophene-alt -diketopyrrolopyrrole-bisthiophene) or PffBTT2-DPPT2) that combines a D-A 1 -D-A 2 copolymer strategy and our temperature-dependent aggregation polymer design. The chemical structure of PffBTT2-DPPT2 is shown in Figure 1 a. While the fi rst acceptor unit (A 1 ) is DPP, 5,6-difl uoro-2,1,3-benzothiadiazole (ffBT) is selected as the second acceptor unit (A 2 ), as it was shown in our previous studies to introduce excellent polymer properties for high-effi ciency PSCs. [ 8 ] Although the bandgap of PffBTT2-DPPT2 is small (1.43 eV), PSCs based on PffBTT2-DPPT2 can still achieve an impressive V OC of 0.81 V, indicating a very small V OC loss of 0.62 V. The bandgap and V OC loss of PffBTT2-DPPT2-based PSCs are very close to the optimal Polymer solar cells (PSCs) have been developed as a promising low-cost and environmentally friendly alternative to conventional inorg...

A novel dual‐functional composite layer composed of a high ionization potential nonconjugated polymer or conjugated molecular material and an inorganic salt of a low work function metal is demonstrated. The composite provides superior hole blocking along with promising electron transport capability and results in good device performance for two model electroluminescent polymers, PFO and MEH‐PPV.

ObjectivesThis study aims to investigate the electrical properties of lumbar paraspinal muscles (LPM) of patients with acute lower back pain (LBP) and to study a new approach, namely Electrical Impedance Myography (EIM), for reliable, low-cost, non-invasive, and real-time assessment of muscle-strained acute LBP.DesignPatients with muscle-strained acute LBP (n = 30) are compared to a healthy reference group (n = 30). Electrical properties of LPM are studied.BackgroundEIM is a novel technique under development for the assessment of neuromuscular disease. Therefore, it is speculated that EIM can be employed for the assessment of muscle-strained acute LBP.MethodsSurface electrodes, in 2-electrode configurations, was used to measure the electrical properties of patient's and healthy subject's LPM at six different frequencies (0.02, 25.02, 50.02, 1000.02, 3000.02, and 5000.02 kHz), with the amplitude of the applied voltage limited to 200 mV. Parameters of impedance (Z), extracellular resistance (Re), intracellular resistance (Ri), and the ratio of extracellular resistance to intracellular resistance (Re/Ri) of LBP patient's and healthy subject's LPM were assessed to see if significant difference in values obtained in muscle-strained acute LBP patients existed.ResultsIntraclass correlation coefficient (ICC) showed that all measurements (ICC>0.96 for all studying parameters: Z, Re, Ri, and Re/Ri) had good reliability and validity. Significant differences were found on Z between LBP patient's and healthy subject's LPM at all studying frequencies, with p<0.05 for all frequencies. It was also found that Re (p<0.05) and Re/Ri (p<0.05) of LBP patient's LPM was significant smaller than that of healthy subjects while Ri (p<0.05) of LBP patient's LPM was significant greater than that of healthy subjects. No statistical significant difference was found between the left and right LPM of LBP patients and healthy subjects on the four studying parameters.ConclusionEIM is a promising technique for assessing muscle-strained acute LBP.

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