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.

The efficiency of polymer based bulk heterojunction (BHJ) solar cells mainly depends on the film morphology of the absorption layer and the interface properties between the stacked layers. A comparative study using atomic force microscopy (AFM) and optical in situ thin film drying measurements is performed. The strong impact of distinct drying scenarios on the polymer:fullerene BHJ layer morphology is investigated by AFM. The AFM images show a systematic dependency of structure sizes at the surface on drying kinetics. In addition thin film optical measurements for the determination of thin film drying kinetics and parameters are performed using a dedicated experimental setup. The data are used as the input for a quantitative simulation of the drying process. The film thickness decreases linearly during drying while the solvent mass fraction decreases moderately over a wide range until it drops rapidly. Subsequently the remaining solvent fraction evaporates considerably slower. Our work gives a fundamental understanding of the film formation kinetics and prerequisites for the systematic optimization of the film morphology in solution processed organic photovoltaic devices.

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The drying process of the bulk heterojunction (BHJ) layer has a strong impact on the solar cell performance for the well-investigated material system P3HT:PC 61 BM. For higher performing low-bandgap polymers and C 71 fullerene derivatives, no comprehensive studies of the BHJ structure evolution during film drying are available. In this work we investigate the structure formation of the low-bandgap polymer poly{[4,40-bis(2-ethylhexyl)dithieno(3,2-b;20,30-d)silole]-2,6-diyl-alt-(2,1,3-benzothidiazole)-4,7-diyl} (PSBTBT) and [6,6]-phenyl C 71 -butyric acid methyl ester (PC 71 BM) in the transition from wet to solid by in-situ grazing incidence Xray diffraction (GIXD) and laser reflectometry simultaneously. The nucleation and crystallization of PSBTBT differs from the interface-induced crystallization of P3HT and occurs partially in the solution. It is shown that PSBTBT:PC 71 BM blend nanomorphology and optoelectronic device properties are rather insensitive to the drying process in the investigated temperature range of 40−85°C. This is beneficial for fast drying at elevated temperatures which enables high throughput fabrication of efficient organic photovoltaics.

From sorption experiments in literature it is known, that the solvent diffusion coefficient in nanoscale polymer layers decreases compared to its value in thicker films due to an increasing influence of the substrate. However, it is unclear whether this behavior is only related to thickness variation or also to concentration dependency, inadequate measurement routines, nonconsidered influence of phase-equilibrium or unsuitable data analysis. Here, we describe a measurement setup on the basis of a quartz crystal microbalance, that allows for a clear differentiation between the parameters thickness and concentration. For the material system poly(vinyl acetate)-methanol, sorption experiments with dry film thicknesses ranging from 50 to 685 nm on SiO 2 and gold surfaces were conducted and analyzed using different evaluation methods. A comparison to micrometerscale data (30 μm) reveals that the phase equilibrium does not vary with film thickness, but the diffusion coefficient decreases by orders of magnitude due to both thickness (10 −13 to 10 −16 m 2 /s) and concentration (10 −11 to 10 −13 m 2 /s). On the basis of the different evaluation methods we propose a model that divides the diffusional characteristics in two zones: a top layer with bulk-like behavior and a substrate-near region where solvent diffusion is significantly slower.

The use of solvent additives has become a successful strategy to control the structural evolution upon film formation in bulk-heterojunction (BHJ) solar cells. Nonetheless, a complete understanding of the additive's role in the phase separation mechanisms and organization of donor and acceptor materials in BHJs is still lacking. In this work we gain further insight about the specific role that a widely used additive, 1,8-octanedithiol (ODT), has in the crystallization of both PCPDTBT and PC 71 BM, directly after wet film deposition using blade-coating. By in situ X-ray scattering and optical reflectometry, we correlate the additive-driven crystallization with the evolution of film composition from the earliest time of solvent evaporation. It is shown that ODT influences the evolution of both PCPDTBT and PC 71 BM. ODT leads to prolonged crystallization time during the ODT-drying dominated period corresponding to an overall solvent content (x) of 75 wt % > x > 15 wt % and delays the onset of PC 71 BM aggregation to x < 20 wt %, being pushed out of the crystalline polymer domains.

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Um Klimaneutralität zu erreichen sind Maßnahmen mit verschiedenen Ansatzpunkten notwendig. Prozesse müssen neu entwickelt und elektrifiziert werden. Besonders in der Übergangsphase müssen die Verbräuche und Emissionen korrekt erfasst werden, damit die neuen Prozesse in Zukunft mit maximaler Effizienz vollautomatisch gefahren werden können. Die Automatisierung und die Digitalisierung, hierbei die Messung von Betriebszuständen und die Kombination verschiedener Datenquellen,spielen eine Hauptrolle in dieser Umsetzung. In diesem Beitrag wird ein Weg geschildert, die Energieeffizienz zu verbessern, die CO2e-Emissionen zu analysieren und mit den richtig priorisierten Maßnahmen die Reduktion der Emission von Treibhausgasen zu erreichen. Die Möglichkeiten und Anforderungen an die  Automatisierungstechnik werden in diesem Kontext beleuchtet, damit die Automatisierung weiter als Enabler für die notwendige Verbesserung dienen kann.