Role of Solvent Trapping Effects in Determining the Structure and Morphology of Ternary Blend Organic Devices

We present results of scanning transmission X-ray microscopy (STXM) measurements of bulk heterojunction organic solar cells built from a ternary blend of poly(3-hexylthiophene) (P3HT), [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), and [2,3,12,13-tetracyano-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrinato]copper(II) (Cu(CN)(4)R porphyrin. These results show evidence of solvent trapping due to porphyrin in the film. Upon annealing, submicrometer depressions are observed in the ternary blend films, corresponding to the evolution of solvent that is associated with the small porphyrin aggregates that phase segregate in the middle of the depressions. The areal density and size of the depressions change systematically with porphyrin concentration in the ternary blend. The relationship of the observed morphologies to the previously measured device performance is discussed.