近年来，以稠环电子受体为活性层的有机太阳能电池 (OSCs) 光电转换效率 (PCE) 已经超过18%，推动了有机太阳能电池的快速发展。目前，然而，高性能的稠环电子受体材料合成路线冗长、价格昂贵，成为未来商业应用的瓶颈。作为比较，非稠环电子受体由于合成简单且成本低，近年来逐渐受到人们的关注。然而，基于非稠环电子受体的OSCs的PCE较低。所以，建立分子结构、光电物理性质与光伏性能之间的关系，进一步开发高性能非稠环电子受体显得尤为重要。该博士学位论文聚焦于非稠环电子受体材料的分子设计、合成以及光伏性能研究，主要内容如下：
一、合成了四种结构简单的非稠环电子受体H-2F、CH3-2F、OCH3-2F和SCH3-2F。利用大位阻的二苯胺衍生物作为侧基，构建三芳胺单元，其具有三维分子构型和较强的给电子能力，既能有效抑制分子的过度聚集，又能增强分子内电荷转移效应拓宽吸收光谱。研究表明二苯胺基上的取代基对受体吸收、能级和分子的堆积方式以及共混薄膜的电子迁移率和形貌都有显著影响。单晶分析表明，取代基会影响单分子构型，产生截然不同的分子堆积方式；其中，受体CH3-2F独特的堆积结构，更加有利于电荷传输。最终，基于CH3-2F的有机太阳能电池的光电转换效率最高，为12.28%。
二、在第一个工作的基础上，该博士学位论文以烷基二苯胺为侧链，设计并合成了两种具有不同核心单元和不同分子构型的受体BTh-OC8-2F和DTh-OC8-2F。在S···O分子内相互作用的帮助下，两个受体均能形成平面分子构象。与之不同的是，BTh-OC8-2F具有线性分子骨架，侧链位于分子骨架两侧，结晶性强于分子构型为C形且侧链位于分子骨架同侧的受体DTh-OC8-2F。因此，基于DTh-OC8-2F的共混膜呈现纳米级相分离尺寸、能抑制电荷复合、具有更高效的激子解离效率和更低的非辐射能量损失。基于DTh-OC8-2F:PBDB-T器件的光电转换效率为14.13%，远高于受体BTh-OC8-2F的光电转换效率，11.95%。
三、为考察不同π桥及分子共轭长度对器件性能的影响，设计了三种受体2Th-2F，BTh-Th-2F和2BTh-2F。研究表明，随着共轭π长度的增加，受体的摩尔消光系数和电子迁移率逐渐增大。此外，受体2BTh-2F同时具有S···N和S···O分子内相互作用力，形成平面分子骨架。更重要的是，受体2BTh-2F具有三维网状堆积结构。基于受体2BTh-2F及其衍生物的共混薄膜，纤维结构更明显、更致密。最终，2BTh-2F:PBDB-T的器件具有14.53%的光电转换效率，更重要的是，当选择D18作为给体聚合物时，光电转换效率可以进一步提高到15.44%，这是基于非稠环电子受体的最高PCE，通过进一步的器件制备条件优化，基于该受体的单结电池的效率达到了17%以上，已经可以与高效率的稠环受体相媲美，显示了非稠环受体的巨大发展潜力。

In recent years, fused ring electron acceptors (FREAs) have pushed the rapid development of organic solar cells (OSCs) with power conversion efficiency (PCE) up to over 18%. However, high performance FREAs are difficult to synthesize and expensive, which has become a bottleneck for the future commercial application. As a comparison, the cost-effective nonfused ring electron acceptors (NFREAs) gradually attract more and more attention during the last several years. However, the PCE of NFREAs based OSCs is still far behind that of FREAs. To further develop high-performance NFREAs, it is important to establish the relationship between molecular structure, property and photovltaic performance. The results are summarized as follows: 
1. Four simple NFREAs (H-2F, CH3-2F, OCH3-2F and SCH3-2F) with diphenylamine derivatives as the flanking group are designed and synthesized, which can improve solubility and further avoid oversized aggregates. The substituent group at the diphenylamine unit has a significant influence on the absorption and energy level of acceptors as well as the electron mobility and morphology of the blend films. A single-crystal analysis demonstrates that substituent group affect the single molecule configuration, resulting in completely different molecular stacking modes. Among them, the acceptor CH3-2F has unique stacking structure and favorable for electron transport, and CH3-2F-based OSCs provide the highest PCE of 12.28%. 
2. Two NFREAs BTh-OC8-2F and DTh-OC8-2F with different molecular conformation are designed and synthesized. Both acceptors can form planar molecular conformations by the assistance of S···O interactions. Differently, BTh-OC8-2F with a linear molecular backbone and two trans-arranged side chains at the core unit exhibits too much stronger crystallinity than DTh-OC8-2 with a C-shape molecular conformation and two cis-arranged steric side chains at the core unit. Thus, DTh-OC8-2F based blend films display a better nanoscale phase separation, more suppressed charge recombination, more efficient exciton dissociation, and lower nonradiative energy loss. OSCs based on DTh-OC8-2F can deliver a PCE of 14.13%, which is higher than BTh-OC8-2F based ones (11.95%).
3. Three NFREAs (2Th-2F, BTh-Th-2F and 2BTh-2F) with thieno[3,2-b]thiophene bearing two bis(4-butylphenyl)amino substituents as the core, 3-octylthiophene or 3-octylthieno[3,2-b]thiophene as the spacer, and 3-(1,1-dicyanomethylene)-5,6-difluoro-1-indanone as the terminal group are designed and synthesized. The molar extinction coefficient of acceptors and the electron mobility of blend films gradually increase with increasing the π-conjugation length. Moreover, 2BTh-2F displays a planar molecular conformation assisted by S···N and S···O intramolecular interactions. More importantly, the molecular stacking changes from 2D packing for 2Th-2F analogue to 3D network packing for 2BTh-2F. Due to these comprehensive merits, 2BTh-2F:PBDB-T based OSCs give a high PCE of 14.53%. More impressively, when D18 is used as the donor polymer, the PCE is enhanced to 15.44%, which is the highest value reported for OSCs based on NFREAs, further optimized the devices, a high PCE over 17% was obtained, which can compare with the high performance FREAs, indicating the large potential of the simple NFREAs.