Morphology Development in Amorphous Polymer:Fullerene Photovoltaic Blend Films During Solution Casting

Pearson, Andrew J.; Wang, Tao; Dunbar, Alan D. F.; Huang, Yi; Watters, Darren C.; Coles, David M.; Staniec, Paul A.; Iraqi, Ahmed; Jones, Richard; Lidzey, David G.

doi:10.1002/adfm.201301922

Cited by 56 publications

(45 citation statements)

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“…The latter occurred in a relatively thin region of less than two microns, where the molecular arrangements during film formation caused major changes in the optical constants, thus the loss of interference. 21 The drying period below 2 mm cannot be resolved quantitatively by our thickness calculation approach. Nevertheless, it is observed that this final phase of film formation had a slightly slower drying behavior, as the final WLR signal deviated from the extrapolation of the linear behavior.…”

Section: 30mentioning

confidence: 97%

“…7,8,[10][11][12][13][14][15][16][17][18] Instead of reflectometry, some investigations have employed spectroscopic ellipsometry (SE), which is more sensitive to sub-nanometer regions, allowing the user to probe final stages of thin film drying. [19][20][21] Additionally, laser light and X-ray scattering techniques are used either as stand-alone methods or in combination with other optical methods. While laser light scattering has been used as a tool to investigate liquid-liquid phase separation in organic blends, grazingincidence X-ray scattering, with its wide (GIWAXS) and small angle (GISAXS) forms, has become a very powerful technique to investigate periodic ordering and domain formation in organic thin films, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, in the last few years in situ measurements from blading and bar spreading methods became as popular as spin coating due to their similarities to industrial-scale printing methods. 7,8,[11][12][13][14][15]20,21,23,25 Nevertheless, regardless of whether spin coating is selected or doctor blading, in situ characterization methods are mostly utilized to get deeper insight into the morphology and correlate this information with device performance. There is a very limited amount of reports which studied the precision of solution formulation and drying conditions on the thermodynamics and kinetics of the BHJ thin film drying, thus the current knowledge is still far from building a road map for better solution formulations and drying conditions, which could be transferred to large-scale processing for further optimizations.…”

Section: Introductionmentioning

confidence: 99%

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Real-time evaluation of thin film drying kinetics using an advanced, multi-probe optical setup

et al. 2016

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a Solution-processed organic photovoltaic devices are advantageous due to their low-cost large area manufacturing techniques, such as slot-die coating, gravure printing and roll-to-roll coating. The final microstructure of a polymer:fullerene bulk-heterojunction (BHJ) film is a fine interplay between solution thermodynamics (e.g. solubility, miscibility. . .) and kinetics (e.g. solvent evaporation, polymer ordering, phase separation. . .) during the drying process. In order to design better performing organic photovoltaic devices, gaining knowledge over the drying properties of polymer:fullerene thin films is essential.A novel in situ thin film drying characterization chamber, equipped with white-light reflectometry, laser light scattering and photoluminescence, is presented in combination with grazing-incidence X-ray diffraction on two different polymer:fullerene bulk heterojunctions based on poly-(3-hexylthiophene-2,5-diyl) (P3HT) and polythieno [3,2b]thiophene-diketopyrrolopyrrole-co-thiophene (DPP-TT-T) polymers.With photoluminescence applied for the first time as an in situ method for such drying studies, these single-chamber measurements track the fine interplay between thermodynamics and kinetics of thin film drying and provide invaluable information on solution behavior and microstructure formation.

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Section: 30mentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Real-time evaluation of thin film drying kinetics using an advanced, multi-probe optical setup

et al. 2016

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“…The dynamics of solvent evaporation and phase separation govern the final structure. In situ studies have been performed on timescales corresponding to realistic processing conditions for practical applications [31][32][33][34] . However, in none of these systems co-solvents are necessary to decrease domain sizes.…”

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A real-time study of the benefits of co-solvents in polymer solar cell processing

et al. 2015

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The photoactive layer of organic solar cells consists of a nanoscale blend of electron-donating and electron-accepting organic semiconductors. Controlling the degree of phase separation between these components is crucial to reach efficient solar cells. In solution-processed polymer-fullerene solar cells, small amounts of co-solvents are commonly used to avoid the formation of undesired large fullerene domains that reduce performance. There is an ongoing discussion about the origin of this effect. To clarify the role of co-solvents, we combine three optical measurements to investigate layer thickness, phase separation and polymer aggregation in real time during solvent evaporation under realistic processing conditions. Without co-solvent, large fullerene-rich domains form via liquid-liquid phase separation at B20 vol% solid content. Under such supersaturated conditions, co-solvents induce polymer aggregation below 20 vol% solids and prevent the formation of large domains. This rationalizes the formation of intimately mixed films that give high-efficient solar cells for the materials studied.

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“…Using reflectance imaging we could identify the higher performing areas as areas with a higher wet film drying rate. To probe the evolution of the morphology in-situ x-ray scattering has been used to determine the onset of crystallization for semi-crystalline polymers [73,76] and for PCBM [73,77]. Recently also an optical method to probe the morphology formation by a combination of absorption, reflectance and scattering was introduced [65].…”

Section: In-situ Morphology Monitoringmentioning

confidence: 99%

Optoelectrical Imaging Methods for Organic Photovoltaic Materials and Moduls

Bergqvist¹

2015

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Linköping 2015 IICover image: LED array based photocurrent imaging method for in-line characterization of printed organic solar cells developed during the course of this thesis. Illustration by Cecilia Kornehed.During the course of research underlying this thesis, Jonas Bergqvist was enrolled in Agora Materiae, a multidisciplinary doctoral program at Linköping University, Sweden. III AbstractTo achieve a high living standard for all people on Earth access to low cost energy is essential. The massive burning of fossil fuels must be drastically reduced if we are to avoid large changes of our climate. Solar cells are both technologically mature and have the potential to meet the huge demand for renewable energy in many countries. The prices for silicon solar cells have decreased rapidly during the course of this thesis and are now in grid parity in many countries.However, the potential for even lower energy costs has driven the research on polymer solar cells, a class of thin film solar cells. Polymer solar cells can be produced by roll to roll printing which potentially enables truly low cost solar cells. However, much research and development remain to reach that target.Polymer solar cells consist of a semiconducting composite material sandwiched between two electrodes, of which one is transparent, to let the light energy in to the semiconductor where it is converted to electric energy. The semiconductor comprise an intimate blend of polymer and fullerenes, where the nanostructure of this blend is crucial for the photo current extraction.To reach higher solar cell performance the dominating strategy is development and fine tuning of new polymers. To estimate their potential as solar cell materials their optical response have been determined by spectroscopic ellipsometry. Furthermore, optical simulations have been performed where the direction dependency of the optical response of the transparent electrode material PEDOT:PSS have been accounted for. The simulations show reduced electrode losses for light incident at large oblique angles.Moreover, we have shown that a gentle annealing of the active layer induces a local conformational changes of an amorphous polymer that is beneficial for solar cell performance. The active layer is deposited from solution where the drying kinetics determine the final nanostructure. We have shown that using in-situ photoluminescence phase separation can be detected during the drying process while a reflectance method have been developed to image lateral variations of solvent evaporation rate.Imaging methods are important tools to detect performance variations over the solar cell area. For this purpose an intermodulation based photo current imaging method have been developed to qualitatively differentiate the major photo current loss mechanisms. In addition, a 1D LED-array photo current imaging method have been developed and verified for high speed in-line characterization of printed organic solar modules. IV Populärvetenskaplig sammanfattningFör att uppnå en hög levnadsstandard för...

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Morphology Development in Amorphous Polymer:Fullerene Photovoltaic Blend Films During Solution Casting

Cited by 56 publications

References 44 publications

Real-time evaluation of thin film drying kinetics using an advanced, multi-probe optical setup

Real-time evaluation of thin film drying kinetics using an advanced, multi-probe optical setup

A real-time study of the benefits of co-solvents in polymer solar cell processing

Optoelectrical Imaging Methods for Organic Photovoltaic Materials and Moduls

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