Gao Yongqian, Grey John K
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
J Am Chem Soc. 2009 Jul 22;131(28):9654-62. doi: 10.1021/ja900636z.
Resonance Raman spectroscopic imaging is introduced as a physical probe to identify and spatially map morphology-dependent variations of intra- and interchain interactions and order in poly-3-hexylthiophene (P3HT) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) photovoltaic blend thin films. Absorption spectra and C=C symmetric stretching Raman modes of P3HT/PCBM blend films show contributions from two distinct species that are assigned as aggregated and unaggregated P3HT chains with characteristic Raman frequencies of approximately 1450 (I(C=C)(agg)) and approximately 1470 cm(-1) (I(C=C)(un)), respectively. Upon thermal annealing of blend films, the relative concentrations of I(C=C)(agg) and I(C=C)(un) species (R = I(C=C)(agg)/I(C=C)(un)) changes on average from 0.79 +/- 0.20 (as-cast) to 2.45 +/- 0.77 (annealed). It is proposed that R values report on the relative densities of states (DOS) of aggregated and unaggregated species, and resonance Raman imaging is then used to spatially map morphology-dependent variations of R values and uncover subclassifications of these species. From both R and frequency dispersion resonance Raman images of I(C=C)(agg) and I(C=C)(un) species, four distinct types of P3HT chains are identified and mapped in annealed P3HT/PCBM blend thin films: (i) highly aggregated/crystalline, (ii) partially aggregated, (iii) interfacial, and (iv) unaggregated/PCBM rich. The change in aggregation upon annealing is attributed to an increase in planarity of the P3HT chains that is determined from the ratios of C=C/C-C symmetric stretching mode intensities.
共振拉曼光谱成像作为一种物理探针被引入，用于识别和空间映射聚3-己基噻吩（P3HT）和[6,6]-苯基-C61-丁酸甲酯（PCBM）光伏共混薄膜中链内和链间相互作用及有序性的形态依赖性变化。P3HT/PCBM共混薄膜的吸收光谱和C = C对称拉伸拉曼模式显示出来自两种不同物种的贡献，它们分别被指定为聚集态和非聚集态的P3HT链，其特征拉曼频率分别约为1450（I(C = C)(agg)）和约1470 cm-1（I(C = C)(un)）。在共混薄膜进行热退火后，I(C = C)(agg)和I(C = C)(un)物种的相对浓度（R = I(C = C)(agg)/I(C = C)(un)）平均从0.79±0.20（铸态）变为2.45±0.77（退火态）。有人提出R值反映了聚集态和非聚集态物种的相对态密度（DOS），然后共振拉曼成像被用于空间映射R值的形态依赖性变化，并揭示这些物种的子分类。从I(C = C)(agg)和I(C = C)(un)物种的R和频散共振拉曼图像中，在退火后的P3HT/PCBM共混薄膜中识别并映射出四种不同类型的P3HT链：（i）高度聚集/结晶的，（ii）部分聚集的，（iii）界面的，以及（iv）非聚集/富含PCBM的。退火后聚集情况的变化归因于由C = C/C - C对称拉伸模式强度比确定的P3HT链平面度的增加。
