新型二苯基吡喃烯类材料的设计合成及在本体异质结太阳能电池中的光伏性能研究

Currently in the research of organic bulk-heterojunction (BHJ) solar cells, it is desirable to explore novel electron-donating materials that have advantages such as strong UV-Visible absorption, well-matched energy levels with fullerene materials and good solubility. Diphenylpyranylidenes have intense absorptions in the visible region as well as proper HOMO energy levels adjustable by introducing substituents at the end of the phenyl groups. In addtion, diphenylpyranylidenes can be simply prepared and various π-conjugated parts can be combined with the diphenylpyranylidenes, which are helpful to adjust the energy level and extend the absorption region of target molecule. In this project, we will apply diphenylpyranylidenes moiety to the molecular structure of electron donating materials in the BHJ solar cells with following two directions: (1) it will be introduced as side chain in the polythiophene core part; (2) it will be combined with electron-withdrawing cyanoacetonitrile moiety for developing a novel π-conjugated small molecule with push-pull structure. After the systhesis of new electron donating molecules, their thin-film morphology will be optimized for fabricating solution-processable organic bulk-heterojunction (BHJ) solar cells. Through the extended optical absorption spectra and well-tuned energy levels of novel materials with diphenylpyranylidene functional group, we can improve the electron-hole charge separation and charge transfer during the process of Photon-to-Electron Conversion. Furthermore, power conversion efficiency will be enhanced. This research will provide the theoretical support and experimental basis for developing organic solar cells with high photovoltaic performance and stability.

目前本体异质结有机太阳能电池给体材料存在紫外可见光吸收弱、与富乐烯受体材料能级匹配度差、材料来源不够多元化等问题。本项目拟用二苯基吡喃烯这类具有宽光谱强吸收、合成简单、空穴传输能力良好的材料，完成具有二苯基吡喃烯侧基链的噻吩聚合物给体和二苯基吡喃烯给体、丙二腈受体相结合的新型电子推拉结构式小分子给体的设计合成，然后通过改善材料的薄膜界面和形貌，利用溶液加工方法制备相应的本体异质结有机太阳能电池，构筑新材料结构与光伏特性的构效关系，最后拟达到有效扩展给体材料的可见光吸收范围，优化光活性层间的能级匹配，提高电荷分离效率和载流子传输率的目标，为高性能高稳定性有机太阳能电池的制备提供理论与实验依据。这对发展具有低成本、轻便性、柔软性和可大面积化制备的有机太阳能电池具有重大意义。

应用于聚合物太阳能电池的D-A型共轭聚合物虽然可以有效扩大光吸收范围，但在紫外光区和部分可见光区吸收强度较弱，通常，导入共轭型芳香基团可以调节聚合物的光响应能力和电子轨道能级。本项目以二苯基吡喃烯（DPP）基团为电子给体单元，设计合成了应用于有机太阳能电池的聚合物和小分子材料，利用其具有较强的紫外可见光范围内的吸收光谱和强供电子能力等优点，致力于提高器件光吸收效率并对分子轨道能级进行调节。研究结果表明，二苯基吡喃烯侧链加入聚(3-己基噻吩)(P3HT)主链后，在320-450 nm处明显得到光吸收的强度提高，P3HT光吸收在400-650 nm区域，形成了更大程度的互补。在同条件制备和测试太阳能电池后，DPP侧链的导入使电池具有更高的开路电压Voc，最高为0.69 V（相同条件下P3HT器件的Voc值为0.59V）。此外，实际研究中发现DPP功能团分子结构的平面性不足，更适合于在染料敏化太阳能电池(DSC)中作为敏化剂材料，以得到优异的光电转换效率。对称型双锚定二苯基吡喃烯染料分子W2相比于单一锚定基团结构染料分子W1，对共吸附剂有更好的竞争性吸附能力，对二氧化钛薄膜的耦合作用更强。将染料N719与W2进行共敏化后器件的光电转化效率达到8.49％，高于单一N719染料DSSC的效率（7.77％）。这种性能的提高是由于在325-475 nm波长范围内，染料W2的摩尔消光系数高于N719的三倍所致，使钌染料光捕获能力得到了良好的补充。为探索分子结构与光伏性能之间的关系，进一步合成了三种吡喃异构体染料DO，DM和DP，并将其与N719染料共敏化。与标准N719基DSC相比，最具有立体结构的DM分子与N719的共敏化系统将光电转换效率（PCE）从7.60％提高到8.96％，提高18％。此共敏系统的短路光电流密度（Jsc）和开路电压（Voc）均得到优化，这是由于引入DM共敏剂后，N719染料吸附量保持良好，并且染料分子的堆叠行为也得到有效抑制。