Quantitative Bimolecular Recombination in Organic Photovoltaics through Triplet Exciton Formation

被引:93
作者
Chow, Philip C. Y. [1 ]
Gelinas, Simon [1 ]
Rao, Akshay [1 ]
Friend, Richard H. [1 ]
机构
[1] Univ Cambridge, Cavendish Lab, Cambridge CB3 0HE, England
基金
英国工程与自然科学研究理事会;
关键词
CHARGE-TRANSFER EXCITONS; SOLAR-CELLS; STATE DYNAMICS; POLYMER; MORPHOLOGY; EFFICIENCY; ANNIHILATION; ADDITIVES; ENERGY;
D O I
10.1021/ja410092n
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
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-ethylhexy1)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] and [6,6]-phenyl-C-71-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 similar to 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).
引用
收藏
页码:3424 / 3429
页数:6
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