从导电聚吡咯到共轭聚合物光伏材料——我在中科院化学所30年共轭高分子研究历程

From Conducting Polypyrrole to Conjugated Polymer Photovoltaic Materials——My 30 Years Research Carrier on Conjugated Polymers in ICCAS

本文简要回顾了本人在中科院化学所30年的研究历程,重点介绍了在共轭高分子(包括导电聚吡咯电化学、聚合物发光电化学池(LEC)和共轭聚合物给体光伏材料)方面的研究成果。在导电聚吡咯电化学方面,对导电聚吡咯的电化学制备和电化学性质进行了深入研究,阐明了各种电化学聚合条件对制备的导电聚吡咯电导和力学强度等的影响,发现电解液溶剂给电子性(Donor number)对吡咯电化学聚合制备的导电聚吡咯电导的影响:溶剂Donor number越小制备的导电聚吡咯电导越高;使用非离子表面活性剂添加剂在水溶液中制备出表面非常光滑和高力学强度的导电聚吡咯薄膜;对于吡咯电化学聚合提出了电解液阴离子参与的阳离子自由基聚合机理,并推到出吡咯电化学聚合反应的动力学方程;发现在NaNO3水溶液中电化学聚合制备的导电聚吡咯除存在主链氧化、对阴离子掺杂结构外,还存在质子酸掺杂结构;阐明了导电聚吡咯在水溶液中电化学还原和再氧化的机理及其电化学过程的可逆性和稳定性,以及导电聚吡咯在有机电解液中特殊的第一次还原和再氧化的机理。在LEC方面,通过交流阻抗法确认了LEC的电化学掺杂机理和p-i-n结构,合成了多种适用于LEC的主链带离子导电单元的兼具离子导电性的发光嵌段共聚物,避免了LEC活性层中存在的发光聚合物和离子导电聚合物的分相问题;使用离子液体作为电解质制备了室温准冷冻p-i-n结LEC,改善了LEC的电致发光性能。在共轭聚合物给体光伏材料方面,我们提出了通过共轭侧链来拓宽聚合物吸收和提高空穴迁移率的分子设计思想,设计和合成了一系列带共轭侧链的二维共轭聚噻吩衍生物以及基于二噻吩取代苯并二噻吩的窄带隙高效二维共轭聚合物给体光伏材料。我们使用烷硫基取代进一步降低了这类二维共轭聚合物的HOMO能级从而进一步提高了其光伏性能。最后介绍了本组二维共轭聚合物给体光伏材料在非富勒烯聚合物太阳能电池方面的最新研究进展。

This article briefly introduces my 30 years research carrier on conjugated polymers in Institute of Chemistry, Chinese Academy of Sciences （ICCAS）. The achievements mentioned here mainly focus on the fields ol con）ugated polymers, including the electrochemistry of conducting polypyrrole （PPy）, polymer light-emitting electrochemical cells （LECs） and conjugated polymer donor materials for polymer solar cells （PSCs）. In the field of electrochemistry of conducting PPy, I and my group systematically studied the electrochemical preparation and electrochemical properties of conducting PPy. We elucidated the effects of various electropolymerization conditions on conductivity and mechanical properties of the as-prepared PPy films. We found that donor number of the electrolyte solvents greatly influences the conductivity of the as-prepared PPy films., the smaller the donor number of the electrolyte solvent, the greater the electric conductivity of the as-prepared PPy films. Very smooth conducting PPy films with high mechanical strength were prepared by using non ionic surfactant additive in the aquesous electrolyte solution. For the reaction mechanism of pyrrole electropolymerization, I proposed and confirmed the solutionsparticipated cation-radical electropolymerization mechanism, and deduced a kinetic equation for the pyrrole eleetropolymerization reaction. We also found that there are two doping structures （main chain oxidized with counter-anions doping structure and the proton-acid doping structure） in the conducting PPy films prepared from NaNO3 aqueous solution. We studied and elucidated mechanisms of the reduction and re-oxidation of conducting PPy films in aqueous solutions, and the mechanisms of the first reduction and re-oxidation of conducting PPy films in organic electrolyte solutions. In the studies of LECs, I confirmed the electrochemical doping mechanism and the formation of p-i-n structure of the LECs after applying voltage higher than Eg/e of the luminescent conjugated polymers by ac impedance measurements. We synthesized a series of luminescent and ionic conductive conjugated polymers with main chian containing ionic-conducting units, and the phase separation problem in the LECs was avoided by using the bi-functional polymers as the luminescent polymers in the LECs. We fabricated quasi-frozen junction LECs by using ionic liquid as electrolyte salt in the active layers of LECs which improved the electroluminescent properties of the LECs significantly. In the studies of conjugated polymer donor materials for PSCs, we proposed a molecular design strategy of two- dimension （2D）-conjugated polymers with conjugated side chains to broaden the absorption and enhance the hole mobility of the conjugated polymers for improving its photovoltaic performance. We synthesized a series of 2D-conjugated polythiophenes with conjugated side chains which show broader absorption, higher hole mobility and improved photovoltaic performance. Then the 2D-conjugation strategy was further extended to the narrow bandgap 2D-conjugated PBDTTTs by attaching thiophene conjugated side chains on benzodithiophene （BDT） units. We introduced alkylthio substituents on the thiophene conjugated side chains of the 2D-conjugated PBDTTTs and further improved their photovoltaic properties. Finally, I introduced our recent research progress on non-fullerene PSCs based on our 2D-conjugated polymers as donor and narrow handgap n-type organic semiconductor as acceptor.