Cavendish Laboratory, University of Cambridge , J.J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom.
J Am Chem Soc. 2014 Mar 5;136(9):3424-9. doi: 10.1021/ja410092n. Epub 2014 Feb 21.
The nanoscale morphology and high charge densities in organic photovoltaics (OPVs) lead to a high rate of bimolecular encounters between spin-uncorrelated electrons and holes. This process can lead to the formation of low-energy triplet excitons on the donor polymer that decay nonradiatively and limit the device performance. We use time-resolved optical spectroscopy to characterize the effect of morphology through the use of solvent additives such as 1,8-octanedithiol (ODT) on triplet dynamics and charge recombination in blends of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] and [6,6]-phenyl-C71-butyric acid methyl ester. This is an attractive OPV system since the extended absorption of the polymer into the near-infrared gives good coverage of the solar spectrum, but nevertheless, the internal quantum efficiency (IQE) has not been reported to be higher than ~65% under short circuit conditions. We find that, without ODT, the IQE is 48% and 16% of excitations decay via bimolecular triplet formation. With ODT treatment, which improves crystallinity and carrier mobility, the IQE increases to 65%, but bimolecular triplet formation significantly increases and now accounts for all of the recombination (35% of charges).
有机光伏器件（OPVs）中的纳米级形态和高电荷密度导致自旋不相关电子和空穴之间的双分子碰撞速率很高。这一过程会导致给体聚合物上形成低能三重态激子，这些激子无辐射衰减，从而限制了器件性能。我们使用时间分辨光学光谱法通过使用溶剂添加剂（如 1,8-辛二硫醇（ODT））来表征形态对混合体中三重态动力学和电荷复合的影响，该混合体由聚[2,6-(4,4-双(2-乙基己基)-4H-环戊二烯并[2,1-b;3,4-b']-二噻吩)-交替-4,7-(2,1,3-苯并噻二唑)]和[6,6]-苯基-C71-丁酸甲酯组成。这是一种很有吸引力的 OPV 体系，因为聚合物的扩展吸收进入近红外区域，很好地覆盖了太阳光谱，但尽管如此，短路条件下的内部量子效率（IQE）尚未报道高于~65%。我们发现，没有 ODT 时，IQE 为 48%，16%的激发通过双分子三重态形成衰减。通过 ODT 处理，可以提高结晶度和载流子迁移率，IQE 增加到 65%，但双分子三重态形成显著增加，现在占所有复合（35%的电荷）。
