Understanding the Reduced Efficiencies of Organic Solar Cells Employing Fullerene Multiadducts as Acceptors
Understanding the Reduced Efficiencies of Organic Solar Cells Employing Fullerene Multiadducts as Acceptors
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DOI：
10.1002/aenm.201200673
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发表时间：
2013-06-01
影响因子：
27.8
通讯作者：
Nelson, Jenny
中科院分区：
文献类型：
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作者：
Faist, Mark A.;Shoaee, Safa;Nelson, Jenny
富勒烯与两个或两个以上的加合物作为受体的使用最近被证明可以提高以聚（3-己基噻吩）（P3HT）为供体的大块异质结太阳能电池的性能。这种增强是由于从单加合物到多加合物时富勒烯最低未占据分子轨道（LUMO）水平的上升导致开路电压的大幅增加。虽然开路电压的增加是由许多不同的聚合物获得的，但除P3HT外，大多数聚合物在与富勒烯多加合物如双pcbm（苯基- c61 -丁酸甲酯的双加合物）或独立C60双加合物ICBA混合时，光电流显着降低。本文研究了光电流减小的原因。我们发现，这可以部分归因于电荷产生效率的损失，这可能与在供体-受体异质结处的LUMO-LUMO和HOMO-HOMO（最高占据分子轨道）偏移有关，部分归因于电荷载流子收集效率的降低。我们发现P3HT由于与单和多加合富勒烯的高空穴和电子迁移率而表现出有效的收集。相比之下，结晶度较低的聚合物聚[[9-（1-辛基壬基）- 9h -咔唑-2,7-二基]-2,5-噻吩二基-2,1,3-苯并噻吩二唑-4,7-二基-2,5-噻吩二基]（pcdbt）表现出低效的载流子收集，这是由于聚合物中的空穴迁移率低，与多加合物富勒烯混合时电子迁移率低。
The use of fullerenes with two or more adducts as acceptors has been recently shown to enhance the performance of bulk-heterojunction solar cells using poly(3-hexylthiophene) (P3HT) as the donor. The enhancement is caused by a substantial increase in the open-circuit voltage due to a rise in the fullerene lowest unoccupied molecular orbital (LUMO) level when going from monoadducts to multiadducts. While the increase in the open-circuit voltage is obtained with many different polymers, most polymers other than P3HT show a substantially reduced photocurrent when blended with fullerene multiadducts like bis-PCBM (bis adduct of Phenyl-C61-butyric acid methyl ester) or the indene C60 bis-adduct ICBA. Here we investigate the reasons for this decrease in photocurrent. We find that it can be attributed partly to a loss in charge generation efficiency that may be related to the LUMO-LUMO and HOMO-HOMO (highest occupied molecular orbital) offsets at the donor-acceptor heterojunction, and partly to reduced charge carrier collection efficiencies. We show that the P3HT exhibits efficient collection due to high hole and electron mobilities with mono- and multiadduct fullerenes. In contrast the less crystalline polymer Poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl (PCDTBT) shows inefficient charge carrier collection, assigned to low hole mobility in the polymer and low electron mobility when blended with multiadduct fullerenes.