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The efficiency of organic bulk heterojunction solar cells strongly depends on the multiscale morphology of the interpenetrating polymer-fullerene network. Understanding the molecular assembly and the identification of influencing parameters is essential for a systematic optimization of such devices. Here, we investigate the molecular ordering during the drying of doctor-bladed polymer-fullerene blends on PEDOT:PSS-coated substrates simultaneously using in situ grazing incidence X-ray diffraction (GIXD) and laser reflectometry. In the process of blend crystallization, we observe the nucleation of well-aligned P3HT crystallites in edge-on orientation at the interface at the instant when P3HT solubility is crossed. A comparison of the real-time GIXD study at ternary blends with the binary phase diagrams of the drying blend film gives evidence of strong polymer-fullerene interactions that impede the crystal growth of PCBM, resulting in the aggregation of PCBM in the final drying stage. A systematic dependence of the film roughness on the drying time after crossing P3HT solubility has been shown. The highest efficiencies have been observed for slow drying at low temperatures which showed the strongest P3HT interchain π-π-ordering along the substrate surface. By adding the "unfriendly" solvent cyclohexanone to a chlorobenzene solution of P3HT:PCBM, the solubility can be crossed prior to the drying process. Such solutions exhibit randomly orientated crystalline structures in the freshly cast film which results in a large crystalline orientation distribution in the dry film that has been shown to be beneficial for solar cell performance.

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One essential process step during electrode processing for Li-ion batteries is the drying of the wet particulate electrode coating. The electrode film solidifies during evaporation of the solvent and a porous film is formed. In this study we focus on the influence of drying temperature on the internal electrode structure of the dry film. Anode slurries that consist of graphite and an aqueous binder system were coated and subsequently dried. To assure defined and controllable drying conditions, a laboratory set-up with a temperaturecontrolled substrate carrier and an impingement dryer was used. To facilitate a scale-up to continuously passed dryers the choice of experimental temperatures was based on a calculation of steady-state temperatures that result from gas temperatures that are commonly applied in industrial drying processes. The delamination behavior of the differently dried electrodes was investigated by means of a 90° peel test. The results show a strong dependency of electrode adhesion on drying temperature. A lower adhesion force at higher temperatures hints to a variation in binder content at the interface between the copper substrate and the coating layer. The formation of a consolidation Downloaded by [University of Manitoba Libraries] at 22:53 26 August 20152 layer at the air-film interface during drying is identified as a possible explanation and a criterion for consolidation layer formation is suggested.

When fabricating battery electrodes, their properties are strongly determined by the adjusted drying parameters. This does not only affect their microstructure in terms of adhesion, but also influences cell performance. The reason is found to be the binder transported to the surface during drying. Herein, it is shown that when thicker electrodes are processed, new challenges arise. On the one hand, loss of adhesion associated with certain drying conditions becomes a more serious problem; on the other hand, cracking occurs at a certain drying rate and with increasing electrode thickness.

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Several high performance polymer:fullerene bulk-heterojunction photo-active layers, deposited from the non-halogenated solvents o-xylene or anisole in combination with the eco-compatible additive p-anisaldehyde, are investigated. The respective solar cells yield excellent power conversion efficiencies up to 9.5%, outperforming reference devices deposited from the commonly used halogenated chlorobenzene/1,8-diiodooctane solvent/additive combination. The impact of the processing solvent on the bulk-heterojunction properties is exemplified on solar cells comprising benzodithiophenethienothiophene co-polymers and functionalized fullerenes (PTB7:PC71BM). The additive p-anisaldehyde improves film formation, enhances polymer order, reduces fullerene agglomeration and shows high volatility, thereby positively affecting layer deposition, improving charge carrier extraction and reducing drying time, the latter being crucial for future large area roll-to-roll device fabrication.

Organic bulk heterojunction (BHJ) solar cells comprising conjugated polymers (as electron donor) and fullerene derivatives (as electron acceptor) deposited from solution make low cost photovoltaic-energy conversion feasible. [ 1 , 2 ] The active layer of BHJ solar cells comprises an interpenetrating network of polymer and fullerene domains that forms during deposition and drying. The energy-conversion process involves the creation of excitons upon light absorption which are dissociated into free charges at the donor/acceptor interface and are further transported towards the respective electrodes. Thus, for a given combination of donor and acceptor materials, the effi ciency of a BHJ critically depends on its nanoscale structural properties. Ideally, BHJs must have a large interface with domain sizes comparable to the exciton diffusion length (a few nano meters) and effective percolation paths to the electrodes, with balanced transport of holes and electrons. In reality, because of the variety and complex interplay of thermodynamic and kinetic factors that infl uence the resulting nanomorphology, optimization of the microstructure and the morphology is a laborious task that involves trialling many processing protocols. [3][4][5] Over recent years numerous studies have been performed on the blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) with the aim of advancing the understanding of the structure-property-performance relationships. The development of P3HT crystalline order with a π -π stacking of the molecules has been found to be an important factor in ensuring suffi cient hole-carrier mobility for charge extraction. [6][7][8] Other structural issues of importance are the relative orientation of P3HT crystallites (due to their anisotropic electrical charge mobility) and the distribution of amorphous P3HT regions (which are expected to affect the electronic interconnection among P3HT domains). [ 6 , 9 ] However, the relative importance of the many implied microstructural features on solar-cell performance and the factors determining the development of specifi c structures during blend solidifi cation are still poorly understood. As many results of studies into the effect of processing conditions on nanomorphology cannot be transferred to an industrially relevant process (because the coating shear forces and solvent-evaporation conditions are different), we have chosen doctor-blading as a lab-scale fabrication method which is scalable to roll-to-roll (R2R) processing. [ 10 , 11 ] Here, the effect of substrate temperature on the structural evolution of P3HT:PCBM blends has been investigated using in situ grazing incidence X-ray scattering (GIXS). In situ X-ray measurements allow real-time observation of the emergence and evolution of the blend microstructure during solvent evaporation. The characterization of the dried fi lms is complemented with ex situ X-ray measurements, optical-absorption data, and the application of atomic force microscopy (AFM) to explore the de...