http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:6938 The morphological evolution of laterally phase-separated polyfluorene blends composed of poly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)-bis-N,N′-phenyl-1,4-phenylenediamine) (PFB) and poly(9,9′-dioctylfluoreneco-benzothiadiazole) (F8BT) has been studied with scanning transmission X-ray microscopy (STXM). The degree of phase separation in the films was regulated by controlling the time spent in a solvent-saturated atmosphere during solution processing, typically between 1 and 6 min. For films with a 5:1 weight ratio of PFB:F8BT, we observe a systematic increase in domain size and domain purity, with the enclosed F8BT-rich domains growing both through coalescence and flow of material across the domain boundary. For 1:1 and 1:5 blends a more complicated evolution of morphology is observed with evidence of additional vertical stratification. For 1:1 blends, primary and secondary phase separation is observed, with the evolution of the PFB-rich phase evolving similar to the 5:1 blend. Interestingly,the PFB-rich spots within the F8BT domain are observed to disappear after around 3 min of morphology evolution. Similar behavior is also seen in 1:5 blends, where a dramatic partial phase inversion is observed. The origin of this transition is attributed to subsequent vertical phase separation, with PFB wetting the substrate/film interface or film/vapor interface or both. In addition to the mechanisms of phase separation, the implications of the observed morphology changes for device performance are also discussed. 2012-01-30T05:07:10.977Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:6934 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)₄P) 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. 2012-01-30T05:07:08.477Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7933 Scanning transmission X-ray microscopy has been used to quantitatively map the composition of P3HT:PCBM blend films in the vicinity of PCBM crystals formed during annealing at 140°C. The observed PCBM concentration profiles around these crystals have been fitted to Fick’s second law of diffusion and the diffusion constant found to be 2.5 x 10⁻¹⁴ m² s⁻¹. The PCBM concentration at the crystal boundary was found to be 19% (v/v) and is interpreted, together with the annealing temperature of 140°C, as a point on the bimodal line of the composition-temperature phase diagram. The diffusion ofPCBM through P3HT is observed to be bulk-dominated, in contrast to the surface/interface-dominated diffusion observed in MDMO-PPV:PCBM blend films by Yang et al. 2011-06-23T23:31:45.967Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3195 poly(9,9‘-dioctylfluorene-co-bis-N,N‘-(4-butylphenyl)-bis-N,N‘-phenyl-1,4-phenylenediamine) (PFB) and poly(9,9‘-dioctylfluorene-co-benzothiadiazole) (F8BT) used in prototype polymer solar cells has been quantitatively mapped using scanning transmission X-ray microscopy (STXM). The resolution of the STXM technique is 50 nm or better, allowing the first nanoscale lateral chemical mapping of this blend system. For 1:1 blend films spin-coated from xylene we find that the F8BT-rich domain is over 90% pure (by weight) and the PFB-rich domain contains 70% PFB. For 5:1 and 1:5 blend films processed from xylene, the minority phases are found to be intermixed, containing as much as 50% by weight of the majority polymer. Films prepared from chloroform with a 1:1 weight ratio have also been imaged but show no features on the length scale of 50 nm or greater. Additionally, the performance of photovoltaic devices fabricated using films prepared in an identical fashion to those prepared for STXM analysis has been evaluated and compared to the performance of chloroform blends with varied weight ratio. By studying the influence of blend composition on device performance in chloroform blends with a uniform morphology, we relate the performance of xylene-processed films to the local blend composition measured by STXM and the degree of nanoscale phase separation. 2010-04-27T05:24:46.992Z ]]>