有机光伏电池是一种可以将太阳能直接转化为电能的装置。由于其具有质轻、便携、可进行大面积卷对卷印刷等优势，而受到了越来越多研究人员的关注。由电子受体和电子给体材料共混而成的活性层是决定有机光伏电池能量转换效率的关键因素之一。目前，常用的受体材料是A-D-A型稠环小分子，给体材料是D-A型共轭聚合物。A-D-A型稠环小分子的合成比较复杂，涉及到的关环反应收率较低，昂贵的材料成本限制了有机光伏的产业化。本论文中，我们设计并合成了一系列低成本A₁-D-A₂-D-A₁型非稠环小分子受体材料和D-A型聚合物给体材料，并通过制备有机光伏器件，深入研究了材料结构与器件性能之间的关系，具体研究内容如下：

1. 设计、合成了一系列A₁-D-A₂-D-A₁型共轭小分子作为电子受体材料。以苯并噻二唑为中心单元的受体小分子BT-IC4F作为参照分子，在其5,6位上分别引入氟原子或烷氧基进行修饰得到了BT2F-IC4F和BTOR-IC4F。通过DFT理论计算发现，这三个小分子的中心单元与桥接单元二噻吩并环戊二烯（CPDT）之间分别存在分子内非共价作用，如S···N，S···F和S···O等，从而均构筑了类似梯形稠环核的结构。而桥接单元CPDT与双氟氰基茚酮端基单元之间同样存在分子内非共价S···O作用进行构象锁定，从而保证了整个分子的平面性。这种利用分子内非共价相互作用设计小分子受体材料的方法，可以避免复杂的关环反应，合成相对简单、收率较高，是一种有效的非富勒烯受体分子合成策略。

2. 将BT-IC4F，BT2F-IC4F和BTOR-IC4F分别作为电子受体材料，与电子给体材料聚合物PBDB-T共混，制备了倒置有机太阳能电池器件。其中，基于BTOR-IC4F的太阳能电池器件取得了最好的光伏性能，光电转换效率达到了11.48%。这主要是由于BTOR-IC4F相比BT-IC4F和BT2F-IC4F具有更好的溶解性和更高的LUMO能级，并且与PBDB-T共混可以获得最佳的活性层膜形貌。同时，经过电压损失测试分析发现，基于BTOR-IC4F的二元光伏器件表现出最低的非辐射能量损失（0.28 eV）和辐射能量损失（0.27 eV）。

3. 合成了两种含有苯并噻二唑（BT）和噻吩（Th）单元的D-A型共轭聚合物PTBT-1和PTBT-2，并将其分别作为电子给体材料与Y6共混制备了有机太阳能电池。这两种聚合物结构简单、合成成本较低。根据有机光伏器件的测试结果，基于PTBT-1的太阳能电池可以获得12.55%的光电转换效率，而基于PTBT-2的电池器件能量转换效率仅为6.18%。后续我们会系统地研究共混膜形貌对其光伏性能的影响。

Solar energy, as a kind of clean and renewable energy, can be directly converted to electricity by organic solar cells (OSCs). Due to their advantages of light weight, mechanical flexibility and the capability of large-area roll-to-roll printing, OSCs have attracted extensive attention from more and more research groups globally. The active layer, a blend of a donor material and an acceptor material, plays a significant role in promoting photovoltaic performance of OSCs. At present, most high-performance fullerene-free OSCs adopt A-D-A type small molecule acceptors (SMAs) and D-A type polymer donors. The syntheses of fused ring electron acceptors are often complicated, low-yield and high-cost. In this thesis, I mainly focus on developing novel low-cost A₁-D-A₂-D-A₁ type small molecule acceptors and D-A type polymer donors. The relationship between the molecular structures and photovoltaic performance is also systemically studied. The main results are as follows:

1. We have designed and synthesized a series of A₁-D-A₂-D-A₁ type small molecule acceptors (BT-IC4F, BT2F-IC4F and BTOR-IC4F). BT-IC4F is synthesized as the reference molecule. BT2F-IC4F and BTOR-IC4F also possess a “ladder-like” core, which is composed of a central benzothiadiazole unit and two flanking 4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene (CPDT) units. The two fluorine atoms or two alkoxyl chains at the 5,6-positions of the benzothiadiazole unit can form F···S or O···S intramolecular noncovalent interactions with the sulfur atoms at the two CPDT units. According to DFT calculations, the central D-A₂-D units of simplified BT-IC4F, BT2F-IC4F and BTOR-IC4F all display good planarity due to the existence of S···N, F···S and S···O intramolecular interactions. Meanwhile, the same outer A₁–D units of the three SMAs exhibit 0° dihedral angles due to S···O intramolecular noncovalent interaction, which can ensure that the whole molecule is conjugated. Our work has demonstrated that the use of intramolecular noncovalent interaction can bypass complicated ring-closure reactions, which is an effective strategy for the synthesis of SMAs with simple synthesis and high yield.

2. The photovoltaic properties of these three acceptors are evaluated with an inverted device architecture, in which wide band-gap polymer PBDB-T is chosen as the electron donor. Consequently, BTOR-IC4F based devices demonstrate a PCE of 11.48%, which is higher than that of BT2F-IC4F (8.45%) and BT-IC4F (9.83%) based devices. Our further results demonstrate that the introduction of alkoxyl chains in BTOR-IC4F can improve the LUMO energy level and solubility, thus beneficial for higher open-circuit voltage and better blend film morphology. Moreover, according to the voltage loss analysis, BTOR-IC4F based devices exhibit the lowest non-radiative and radiative energy losses of 0.28 and 0.27 eV, respectively.

        3. We have synthesized two D-A type polymer donors PTBT-1 and PTBT-2. The structures of these two polymers are simple so that the synthesis of them is low-cost. According to the preliminary test results, PTBT-1 based organic solar cells show a 12.55% power conversion efficiency, while PTBT-2 based devices give a low PCE of 6.18%. Moreover, we will systematically study the influence of the blend film morphology on the photovoltaic performance.