基于侧链不对称喹喔啉聚合物的高效非富勒烯太阳电池

喹喔啉衍生物由于合成简单，易功能化，成本较低等特点在众多领域都有广泛应用。其自身具有平面刚性结构，也是构建光电聚合物的重要单体。基于喹喔啉单元的有机分子化学结构和电子结构可修饰性强，通过骨架、侧链和取代基等修饰，易于调控分子的能级和吸光光谱，因此，当使用喹喔啉体系的共轭给体与球形富勒烯受体(如PCBM)及弱结晶性非富勒烯受体(如ITIC)均可表现出优异的光伏性能。在本工作中，基于结晶性较强的非富勒烯受体(o-IDTBR)，我们首次制备出侧链不对称喹喔啉(简称：不对称喹喔啉)基聚合物(TPQ-1)与之匹配。相比于侧链对称性喹喔啉(简称：对称喹喔啉)(HFQx-T)与o-IDTBR组合，“弱结晶给体-强结晶受体”组合能表现出更佳均匀的相分离尺度，从而获得更高的短路电流及能量转换效率。TPQ-1与o-IDTBR共混后器件效率为8.6%，加入15%的TB7-Th后，器件效率达到9.6%。

Asymmetric Quinoxaline-Based Polymer for High Efficiency Non-Fullerene Solar Cells

Polymer solar cells (PSCs) with bulk heterojunction (BHJ) structures have seen rapid development in recent years. In comparison with their inorganic counterparts, PSCs have some advantages such as low cost, light weight, solution processability, and good mechanical flexibility. However, improvement of the power conversion efficiency (PCE) of PSCs is required for commercial applications. In order to achieve high-performance PSCs, active layers, including donor polymers and acceptors, are very important. Several design principles for conjugated donor polymers in PSCs have emerged, including optimization of the conjugated backbone, side-chains, and substituents. In the past few decades, various classes of electron-donating polymers have been reported for PSCs. Among them, quinoxaline (Qx) is a unique building block for the construction of different optoelectronic polymers because of its planar, rigid, and conjugated structure. Qx derivatives have proven interesting and have been widely employed in many fields. Qx-based conjugated polymers (or small molecules) can be easily modified to match with ball-like fullerene derivatives such as PCBM (6, 6]-phenyl-C₆₁ or C₇₁-butyric acid methyl ester) or weak crystalline non-fullerene acceptors such as 2, 2'-6, 6, 12, 12-tetrakis(4-hexylphenyl)-6, 12, -dihydrodithieno2, 3-d:2', 3'-d']-s-indaceno1, 2-b:5, 6-b']dithiophene-2, 8-diyl]bismethylidyne(3-oxo-1H-indene-2, 1(3H)-diylidene)]]bispropanedinitrile (ITIC). Herein, we synthesized a Qx-based polymer with asymmetric side-chains (TPQ-1). The molecular weight, optical properties, molecular energy levels, and mobilities of TPQ-1 were investigated. Furthermore, the blend morphologies and photovoltaic properties of TPQ-1 using a strong crystalline non-fullerene (NF) acceptor (o-IDTBR) were systematically explored. The photovoltaic performance of TPQ-1 and its symmetric side-chain counterpart, HFQx-T, was compared. The introduction of asymmetric side-chains led to a favorable phase separation when blended with o-IDTBR. As expected, the TPQ-1:o-IDTBR-based devices exhibited a high PCE of 8.6% after thermal annealing (TA). In contrast, the HFQx-T:o-IDTBR-based devices showed a moderate PCE of 5.7%, moreover, the PCE was decreased to 4.6% after TA treatment. More importantly, a low bandgap material, PTB7-Th, was specifically selected as a third component to mix with the TPQ-1:o-IDTBR blend to form highly-efficient ternary PSCs. At an optimal weight ratio (15%) of PTB7-Th addition, a PCE of 9.6% was achieved. In the systems that were investigated, TPQ-1 demonstrated significantly better photovoltaic properties than the HFQx-T-based devices. These results indicate that Qx-based polymers with asymmetric side chains have a bright future in photovoltaic devices.