TBTT型窄带隙有机给体材料的设计、合成及其光伏性能研究

Organic photovoltaic technique has got considerable attention because of the potential advantages, such as low costs and high flexibility. Various high-performance organic donor materials were designed and synthesized by utilizing the push-pull effect between donor and acceptor units. Quite a few mid-bandgap (MBG) donor materials with optical bandgaps of ca. 1.70 eV have afforded high power conversion efficiencies (PCE) of over 8% by utilizing fullerene derivatives as the acceptor materials. Further utilization of sunlight in near-infrared region via decreasing optical bandgaps of materials is one of the most direct and efficient strategies to improve PCEs and has been realized recently, i.e., PCEs of over 10% at 1.5~1.6 eV. Compared with MBG-donor materials, high-performance LBG-donor materials with optical bandgaps of comparable to or less than 1.5 eV is relatively few and is mainly limited to the 2,5-dialkyl-pyrrolo[3,4-c]pyrrole-1,4-dione (DPP)-containing polymers, which can be attributed the scarcity of effective acceptor units with strong electron-withdrawing ability. Thus, we designed in this project new composite acceptor moiety TBTT that is composed of 5-alkyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (TPD) and thieno[3,4-b]thiophene (TT) units. TPD is viewed as one of the most valuable electron-deficient units available for the construction of MBG-polymers. In our design, the incorporation of proaromatic TT units can effectively decrease the optical bandgap by enhancing the quinoidal resonance of the D-A conjugated molecular frameworks. Meanwhile, the weak intramolecular S-S and/or S-O interactions will enhance the molecular planarity together with large pi-surface, which is favorable for improving semiconductivity. New TBTT-type LBG-donor materials can be obtained by combining TBTT with suitable weakly electron-donating units, such as benzodithiophene, in order to obtain reasonable open voltages via keeping HOMO levels adequately low. The key contents of this project include: (1) Design and regioselective synthesis of TBTT moieties; (2) The effect of TT orientations on the photovoltaic performance and its origin; (3) Fine tuning the electronic property, aggregation structure, and hole mobility of materials by further selective functionalization of TPD and TT subunits. By tightly combining material design/synthesis and photovoltaic evaluation, we will be able to screen out high-mobility LBG TBTT-type donor materials with suitable energy levels including small molecules and copolymers, and realize the continuing promotion of the performance of organic solar cells.

有机太阳能电池由于在成本和柔性器件等方面的潜力而受到广泛关注。近年来，利用给受体推拉电子效应人们设计出各种太阳能电池给体材料，不少带隙在1.70 eV左右的材料通过与富勒烯受体共混实现了超过8%的光电转换效率。降低带隙提高太阳光利用率是进一步提高效率最直接有效的策略之一，并且已经得到了证明。本项目设计了复合型受体单元TBTT，其由噻吩酰亚胺（TPD）和噻吩并[3,4-b]噻吩（TT）组成，将TBTT与合适的弱供电子给体单元组合可以获得各种窄带隙光伏给体材料，核心内容包括：（1）TBTT受体单元的设计与选择性合成；（2）TT取向对材料光伏性能的影响及其根源；（3）通过对TPD和TT亚单元进行选择性官能化，进一步调控材料的电子结构、聚集态结构及空穴迁移率。紧密结合材料的设计合成与光伏性能评价，筛选出具有高迁移率且能级匹配的窄带隙光伏给体新材料，以期实现太阳能电池性能的不断提升。

提出通过“增强给受体体系醌式共振”设计构建有机光伏材料的新思路，设计了一类非富勒烯受体新材料ATT-1，通过与广泛应用的给体材料PTB7-Th匹配，光电转化效率高达10.07%。用14pi-电子茚并茚取代ATT-n分子中的引达省并二噻吩设计合成了具有扭曲结构的小分子受体NITI，通过与宽带隙聚合物给体材料匹配实现了高达12.74%的光电转换效率，在此基础上，进一步合成了另一具有平面结构的茚并茚-二噻吩受体材料ZITI，该材料对常用的商用聚合物材料PBDB-T和J71具有很好的兼容性，优化的器件分别可获得最高12.97%和13.18%的效率，并通过中国国家光伏质检中心的验证。半透明有机光伏器件作为能量收集窗户是有机光伏技术最有前景的应用方向之一，受限于太阳光吸收,基于富勒烯受体的单节半透明器件效率相对较低，这可以归因于高透明度和高光电转换效率这对基础性矛盾。通过将ATT-1受体分子缺电子结构单元绕丹宁丙二腈变成更缺电子的3-(二氰基亚甲基)靛酮，设计合成了小带隙受体ATT-2，受益于小带隙ATT-2与窄带隙PTB7-Th 在近红外区的互补性吸收，实现了单结半透明器件7.84%的光电转换效率（透光率为～37%），由此提出“发展非富勒烯受体，遴选电子给体，实现活性层对可见光的高透过率和近红外光利用率”策略，用以实现高性能半透明光伏器件。三元有机太阳能电池保持单节电池结构，在二元活性层中引入吸收互补的第三组分，增强光谱吸收，利用自主发展的噻吩并噻吩类光伏受体新材料NITI，合理选择二元体系，构筑了具有“分级结构”的三元活性层形貌，实现了光电转化效率的大幅提升。优化的三元器件在300nm膜厚可取得13.63%（平均13.20%）光电转换效率，相对二元器件性能提升幅度高达51%和100%，提出了“分级结构”的三元活性层形貌新见解。