高介电常数有机半导体材料与太阳电池器件研究

Developing new generation photovoltaic technology is one of promising strategies to explore renewable energy. Among various photovoltaic technologies, bulk-heterojunction organic solar cells based on organic semiconducting materials have attracted considerable attention due to their flexibility and solution-processability. Currently, organic solar cells are able to offer very high internal quantum efficiencies (100%), external quantum efficiencies (85%), and fill factors (0.8) that are approaching commercialized crystalline silicon solar cells. However, the voltage losses of organic solar cells are normally in the range of 0.7 – 1.0 V, which is much higher than that of crystalline silicon solar cells (0.3 – 0.5 V). As a result, the power conversion efficiency of organic solar cells is limited by their low open-circuit voltage. Theoretically, enhancing the dielectric constant of organic semiconducting materials can decrease exciton binding energy, reduce various recombination losses, and mitigate space charge effect. Consequently, the voltage losses of organic solar cell can be reduced without sacrificing external quantum efficiency, leading to higher power conversion efficiency. In this proposed project, we plan to develop a series of n-type and p-type organic semiconducting materials with high dielectric constants. Based on the synthesis activities, we will be able to obtain relevant molecular design guidelines for developing high dielectric constant organic semiconducting materials, and the optimization protocols for the morphology of blends based on new materials. And finally, the voltage losses of organic solar cells will be significantly reduced and the power conversion efficiencies will be enhanced.

发展新型光伏电池技术是可再生能源开发利用的重要途径。在众多光伏电池技术中，基于有机半导体材料的体异质结有机太阳电池以其柔性、可溶液加工等优点在全球范围内得到高度关注。在决定太阳电池性能的几个关键参数中，有机太阳电池的内/外量子效率、填充因子等已经非常接近商品化的晶体硅太阳电池的水平。然而有机太阳电池一直存在较大的电压损失（0.7 – 1.0 V），远高于晶体硅太阳电池（0.3 – 0.5 V），从而导致开路电压和器件效率较低。理论研究表明，提高有机半导体材料的介电常数可以降低激子结合能，减少多种复合损失，缓解空间电荷效应，从而能够在保证高量子效率的情况下降低电压损失，提升器件效率。本项目将设计开发一系列高介电常数p-型和n-型有机半导体材料，探究提高介电常数的分子设计规律，建立高介电常数材料共混薄膜的形貌优化方法，降低有机太阳电池的电压损失、提升器件效率。

近年来，随着有机光伏材料和器件工艺的快速发展，有机太阳电池的能量转化效率取得了很大进步。然而和无机或钙钛矿光伏器件相比，有机太阳电池的效率仍偏低。这主要是因为有机半导体通常具有较低的相对介电常数，导致其在吸收光子后，所产生的激子很难直接分离形成自由的载流子，而需要额外的能量去分离，这会造成大的能量损失，不利于有机太阳电池器件性能的提升。因此，探究提高有机半导体介电常数的分子设计规律，开发具有高介电常数的有机半导体材料是解决上述问题的关键。在本项目的资助下，我们提出了对共轭骨架进行氟取代、引入极性的噻唑单元、引入氰基、引入B−N共价键、引入枝化寡聚醚链等五个提高有机半导体的偶极矩和介电常数的方法，设计合成了四个系列的高介电常数p-型有机半导体和一个高介电常数n-型有机半导体。以上述高介电常数p-型和n-型有机半导体为基础，开展了有机太阳电池的制备与性能优化，建立了高介电常数材料共混薄膜的形貌优化方法。进一步，详细探究了高介电常数有机半导体材料对太阳电池中电荷产生、电荷复合和器件电压损失的影响，观察到了极性侧链对高介电常数有机半导体及其有机太阳电池器件中的缺陷态密度、能量有序度、能量损失的不利影响，揭示了有机半导体的介电常数与太阳电池器件性能之间的复杂关系，为后续高介电常数有机半导体的开发与光伏器件的研究提供了重要参考。同时，以高介电常数有机半导体为基础，我们还进行了利用绿色加工工艺制备高性能有机太阳电池的探索，开发了含B−N共价键的高介电常数有机半导体，实现了高效率有机太阳电池的真正绿色加工，为有机太阳电池绿色加工开辟了新思路。