有机太阳能电池体系中新型富勒烯类受体材料的研究

Fullerene is known as the best acceptor material in bulk hetero-junction organic photovoltaic (BHJOPV) devices for its outstanding capturing electrons. At present, 10.1% of power conversion efficiency (PCE) has been achieved in BHJOPV. But studying further to obtain higher PCE still remains a challenge. It is found that the high PCE always results from higher open-circuit voltage (Voc), which depends on the lowest unoccupied molecular orbital (LUMO) level of acceptor to a great extent. Fullerene material is a diverse family composed of empty fullerenes, endohedral fullerenes and various fullerene derivatives. It is reported that the LUMO level of Lu3N@C80 derivative is 260 mV higher than that of C60. Meanwhile, the LUMO levels of large cage fullerenes are also higer obviously than those of smaller cage fullerenes. Therefore, it is very meaningful to explore more novel fullerene acceptor materials besides C60 and C70. In the previous study, several novel fullerene derivatives have been designed and synthesized followed by the achievement of OPV devices with excellent properties. In this project, more fullerene derivatives based on metallofullerenes and larger cage fullerenes will be studied to improve Voc further and PCE.

富勒烯具有优良的得电子特性，是构筑本体异质结有机光伏器件最优秀的电子受体材料。目前，本体异质结光伏器件的最高光电转换效率已经达到了10.1%，但如何进一步提高PCE依然是国际竞争的热点。研究发现，提高光伏器件的开路电压是进一步提高其能量转换效率的关键因素之一，而器件开路电压的提高主要依赖于受体材料中LUMO能级的提高。富勒烯是一个由空心富勒烯、金属富勒烯以及各种富勒烯衍生物共同组成的庞大家族。已有研究发现金属富勒烯Lu3N@C80衍生物受体材料比C60同样衍生物的LUMO能级高260 mV之多，大碳笼富勒烯的LUMO能级也要明显高于小碳笼富勒烯，从而展现出大幅提高器件开路电压以及光电转换效率的潜力。在前期青年基金项目的研究工作中，我们通过设计合成新的富勒烯衍生物获得了高性能光伏器件，本项目拟在此基础上研究金属富勒烯衍生物及大碳笼富勒烯衍生物受体材料，提高器件开路电压，获得高光电转换效率。

本项目的研究内容紧密围绕光伏器件中富勒烯与金属富勒烯基受体材料研究展开，取得了如下研究成果：成功合成了富勒烯受体材料NC60BA和NC70BA，与P3HT构筑的有机聚合物太阳能电池的效率分别为5.37%和5.95%；并在此基础上分离出NC60BA四种异构体，与P3HT共混构筑器件后使开路电压提高了60mV并获得了6.3%的能量转制效率，同时证明减少异构体数目是一种提高器件开路电压和效率的有效途径；分离IC60BA异构体得到e-ICBA异构体单晶结构，在同一类型器件中可将开路电压提高50mV，但进一步研究发现此异构体因与P3HT结构不匹配而出现过度相分离，导致器件效率大幅度降低。上述研究结果说明在改变受体LUMO能级提高开路电压的同时，给受体结构匹配也应予以充分考虑。.为获取高效的光伏器件，我们还开展了富勒烯基界面修饰材料的研究工作。设计合成的PCMI:K+，可改善无机ZnO 层与活性层的界面接触情况、降低器件因缺陷引起的载流子的复合、优化能级结构，同时提高器件的开路电压、短路电流密度、填充因子，将PTB7-Th:PC71BM 反向器件结构效率由8.41%提高到10.30%。同时PCMI:K+界面修饰材料也可提升PBDTTT-C-T 体系的器件效率，说明PCMI:K+很有潜力成为一种普适、高效的富勒烯界面修饰材料。上述研究结果均为光伏器件的发展提供了重要参考。