A new silole monomer with two 4-（N,N-dimethylamino）phenyl substitutions on silicon atom as designed and synthesized. Three copolymers PF-N-HPS1, PF-N-HPS10 and PF-N-HPS20 were then obtained by copolymerizations of 2,7-fluorene deriva- tives with the silole monomer at feed ratios of 1%, 10%, and 20%. Their UV-vis absorption, electrochemical, photolumines- cent, and electroluminescent （EL） properties were investigated. PF-N-HPS possessed HOMO levels of -5.25-5.58 eV, and showed green emissions. Using PF-N-HPS as the emissive layer, three different polymer light-emitting diodes were fabricated as device A with ITO/PEDOT/PF-N-HPS/A1, device B with ITO/PEDOT/PF-N-HPS/Ba/A1, and device C with ITO/PEDOT/ PF-N-HPS/TPBI/Ba/A1. For the device A, PF-N-HPS only showed very low EL efficiency of 0.06-0.33 cd/A, indicating that the A1 cathode could not inject electron efficiently to the emissive polymers containing the 4-（N,N-dimethylamino）phenyl groups. For the device B, low work function Ba supplied better electron injections, and the EL efficiency could be improved to 0.85-1.44 cd/A. TPBI with a deep HOMO level of -6.2 eV could enhance electron transport and hole blocking. Thus modi- fied recombinations and largely elevated EL efficiency of 4.56-7.96 cd/A were achieved for the device C. The separation of the emissive layer and metal cathode with the TPBI layer may also suppress exciton quenching at the cathode interface.
LIU ZhiTianHU SuJunZHANG LinHuaCHEN JunWuPENG JunBiaoCAO Yong
Two new conjugated copolymers, PBDT-T6-TTF and PBDT-T12-TTF, were derived from a novel 4-fluorobenzoyl thienothi- ophene （TTF）. In addition, two types of benzodithiophene （BDT） units with 2,3-dihexylthienyl （T6） and 2,3-didodecylthienyl （T12） substituents, respectively, were successfully synthesized. The effect of the dual two-dimensional （2D） substitutions of the building blocks upon the optoelectronic properties of the polymers was investigated. Generally, the two polymers exhibited good solubility and broad absorption, showing similar optical band gaps of ~1.53 eV. However, PBDT-T6-TTF with its shorter alkyl chain length possessed a larger extinction coefficient in thin solid film. The highest occupied molecular orbital （HOMO） level of PBDT-T6-TTF was located at -5.38 eV while that of PBDT-T12-TTF was at -5.51 eV. In space charge-limited- current （SCLC） measurement, PBDT-T6-TTF and PBDT-T12-TTF displayed respective hole mobilities of 3.0~10-~ and 1.6x10 5 cm2 V-1 s-l. In polymer solar cells, PBDT-T6-TTF and PBDT-T12-TTF showed respective power conversion efficiencies （PCEs） of 2.86% and 1.67%. When 1,8-diiodooctane （DIO） was used as the solvent additive, the PCE of PBDT-T6-TTF was remarkably elevated to 4.85%, but the use of DIO for the PBDT-T12-TTF-blend film resulted in a lower PCE of 0.91%. Atomic force microscopy （AFM） indicated that the superior efficiency of PBDT-T6-TTF with 3% DIO （v/v） should be related to the better continuous phase separation of the blend film. Nevertheless, the morphology of the PBDT-T12-TTF deteriorated when the 3% DIO （v/v） was added. Our results suggest that the alkyl-chain length on the 2D BDT units play an important role in determining the optoelectronic properties of dual 2D BDT-TT-based polymers.
Zhulin LiuJiangman SunYongxiang ZhuPeng LiuLianjie ZhangJunwu ChenFei HuangYong Cao
