Experimental Physics VI, Julius-Maximilians-University of Würzburg, D-97074 Würzburg, Germany.
J Phys Chem B. 2011 Nov 24;115(46):13513-8. doi: 10.1021/jp2077215. Epub 2011 Oct 31.
Understanding of degradation mechanisms in polymer:fullerene bulk-heterojunctions on the microscopic level aimed at improving their intrinsic stability is crucial for the breakthrough of organic photovoltaics. These materials are vulnerable to exposure to light and/or oxygen, hence they involve electronic excitations. To unambiguously probe the excited states of various multiplicities and their reactions with oxygen, we applied combined magneto-optical methods based on multifrequency (9 and 275 GHz) electron paramagnetic resonance (EPR), photoluminescence (PL), and PL-detected magnetic resonance (PLDMR) to the conjugated polymer poly(3-hexylthiophene) (P3HT) and polymer:fullerene bulk heterojunctions (P3HT:PCBM; PCBM = [6,6]-phenyl-C(61)-butyric acid methyl ester). We identified two distinct photochemical reaction routes, one being fully reversible and related to the formation of polymer:oxygen charge transfer complexes, the other one, irreversible, being related to the formation of singlet oxygen under participation of bound triplet excitons on the polymer chain. With respect to the blends, we discuss the protective effect of the methanofullerenes on the conjugated polymer bypassing the triplet exciton generation.
富勒烯体异质结的降解机制在微观水平上对于提高其内在稳定性至关重要，这对于有机光伏的突破至关重要。这些材料容易受到光和/或氧气的暴露，因此它们涉及电子激发。为了明确探测各种多重态的激发态及其与氧气的反应，我们应用基于多频（9 和 275 GHz）电子顺磁共振（EPR）、光致发光（PL）和 PL 探测磁共振（PLDMR）的组合磁光方法，对共轭聚合物聚（3-己基噻吩）（P3HT）和聚合物：富勒烯体异质结（P3HT：PCBM；PCBM = [6,6]-苯基-C（61）-丁酸甲酯）进行了研究。我们确定了两种截然不同的光化学反应途径，一种是完全可逆的，与聚合物：氧电荷转移复合物的形成有关，另一种是不可逆的，与聚合物链上结合的三重态激子参与下形成单线态氧有关。对于混合物，我们讨论了甲氧基富勒烯对共轭聚合物的保护作用，该作用绕过了三重态激子的产生。
