Structure Formation in Low-Bandgap Polymer:Fullerene Solar Cell Blends in the Course of Solvent Evaporation

Schmidt‐Hansberg, Benjamin; Klein, Michael F. G.; Sanyal, Monamie; Buss, Felix; Medeiros, Gustavo Q. G. de; Munuera, Carmen; Vorobiev, Alexeï; Colsmann, Alexander; Scharfer, Philip; Lemmer, Uli; Barrena, Esther; Schabel, Wilhelm

doi:10.1021/ma300945k

Cited by 26 publications

(24 citation statements)

References 37 publications

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“…Initially, the dominant source of X-ray scatter (at Q = 1.15 and 1.82 Å −1 ) is from DCB solvent molecules. [ 22,32 ] As the solvent content reduces, the relative intensity of these diffuse solvent scattering rings decreases. At approximately 230 s into the fi lm drying process (corresponding to the point where the relative solid content of the fi lm has substantially increased), X-ray scatter from PCDTBT and PC 70 BM begins to dominate (see Figure 3 (c)).…”

Section: Drying Dynamics Of Pcdtbt:pc 70 Bmmentioning

confidence: 99%

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

Pearson

Wang

Dunbar

et al. 2013

Adv Funct Materials

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659www.MaterialsViews.com wileyonlinelibrary.com . IntroductionThe ability to process photovoltaic devices using solution-based techniques is an attractive proposition [ 1,2 ] owing to the potential for such devices to be manufactured over large areas at low cost. [ 3 ] Organic photovoltaic (OPV) devices are one category of solution processable photovoltaics that have seen a rapid rise in power conversion effi ciency (PCE) [ 4,5 ] and operating lifetime [ 6 ] in recent years, bringing the technology closer to the specifi cations deemed necessary for commercial viability. [ 7,8 ] The photoactive semiconducting layer within these devices is typically composed of a blend of a conjugated polymer and a functionalised fullerene, forming a self-assembled bulk-heterojunction (BHJ) architecture. In addition to the electronic properties of the constituent semiconductors, the structure of the BHJ has been demonstrated to signifi cantly infl uence the efficiency of photocurrent generation. [9][10][11][12] It is presently believed that BHJ fi lms are characterised by a partially phase separated nanoscale morphology, with co-existing regions of pure polymer, pure fullerene and a mixed polymer/ fullerene phase all being present. [13][14][15][16] Effi cient OPVs are in general characterised by structures that exist over a series of length-scales, including organisation at molecular length-scales and the formation of nanoscale percolated networks, with each length-scale having an important infl uence on the processes of photocurrent generation and charge extraction. To optimise BHJ morphology and create an OPV device having a high PCE requires control over many different parameters, including the choice of solvent, the conditions of fi lm casting and the possible application of post-fi lm deposition techniques.Several studies [17][18][19][20][21][22][23][24][25] have applied a range of techniques to probe the formation and evolution of morphology in polymer:fullerene blend fi lms during various stages in their preparation, drying and post processing in order to gain insight into the dynamic mechanisms that drive morphology evolution. [ 26 ] In addition to an improved physical understanding of such processes, the information obtained is likely to be of signifi cant importance if such materials and devices undergo commercialisation and manufacture, as real-time process control will be a critical requirement. To date, the majority of Morphology Development in Amorphous Polymer:Fullerene Photovoltaic Blend Films During Solution CastingAndrew J. Pearson ,* Tao Wang , Alan D. F. Dunbar , Hunan Yi , Darren C. Watters , David M. Coles , Paul A. Staniec , Ahmed Iraqi , Richard A. L. Jones , and David G. Lidzey * The evolution of fi lm structure is reported during solution casting of PCDTBT:PC 70 BM 1:4 wt%, a polymer:fullerene blend system that fi nds application in an organic photovoltaic device. Using the complimentary techniques of grazing-incidence wide-angle X-ray scattering and spectroscopic ellipsometry, a number of distinct proc...

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Section: Drying Dynamics Of Pcdtbt:pc 70 Bmmentioning

confidence: 99%

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

Pearson

Wang

Dunbar

et al. 2013

Adv Funct Materials

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“…This interpretation of the polymer orientation from SE experiments fits well to the time-resolved x-ray analysis that we published earlier, where we found that PSBTBT nucleation takes place in defined orientation at an interface, while randomly oriented aggregates form in the bulk during solvent evaporation. 29 As the degree of PSBTBT∶PC 71 BM anisotropy is similar to the anisotropy of neat PSBTBT, the polymer orientation remains mostly unaffected upon blending with PC 71 BM.…”

Section: Polymersmentioning

confidence: 91%

“…The blend ratios were chosen according to optimized process protocols. 27,29 SE data of the neat polymer films and the blend films were recorded between 250 and 1,700 nm at different angles of incidence α between 30 and 80 deg in 5 deg steps. Datasets were analyzed over the entire spectral range.…”

Section: Materials and Sample Preparationmentioning

confidence: 99%

“…PSBTBT and PCPDTBT are wellknown donor-acceptor copolymers with good power conversion efficiencies when blended with PC 71 BM. [27][28][29][30][31] Their similar structures allow a direct comparison. For the active layer deposition and blend ratios, we follow literature-known process protocols, which are optimized for high-performance solar cells.…”

Section: Introductionmentioning

confidence: 99%

“…For the active layer deposition and blend ratios, we follow literature-known process protocols, which are optimized for high-performance solar cells. [27][28][29] Optical data are presented in the spectral region from 250 to 1,000 nm.…”

Section: Introductionmentioning

confidence: 99%

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Modeling approach to derive the anisotropic complex refractive index of polymer:fullerene blends for organic solar cells utilizing spectroscopic ellipsometry

et al. 2015

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Abstract. The knowledge of the complex refractive indices of all thin layers in organic solar cells (OSCs) is a prerequisite for comprehensive optical device simulations that are particularly important for sophisticated device architectures, such as tandem OSCs. Therefore, refractive indices are often determined via spectroscopic ellipsometry and subsequent time-consuming modeling. Here, we investigate a modeling approach that allows for the determination of complex refractive indices of bulk-heterojunctions by superimposing the optical models of the respective fullerenes and polymers. The optical constants of neat [6,6]-phenyl C 71 -butyric acid methyl ester (PC 71 BM), poly{[4,4'-bis(2-ethylhexyl)dithieno(3,2-b;2',3'-d)silole]-2,6-diyl-alt-(2,1,3-benzothidiazole)-4,7-diyl} (PSBTBT) and poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole) (PCPDTBT) are determined, covering the OSC relevant spectral region from 250 to 1,000 nm. Then the blends PSBTBT∶PC 71 BM and PCPDTBT∶PC 71 BM are described within an effective medium approximation. From this approximation, the mass density ratio of polymer and fullerene can be derived. This approach furthermore allows for a uniaxial anisotropic optical description of the polymers and provides insight into thin-film morphology. In contrast to x-ray diffraction experiments, this method also allows for probing amorphous materials. Spectroscopic ellipsometry can be a valuable tool for the investigation of bulk-heterojunction morphologies of the latest highperformance OSC materials that exhibit a low degree of crystallinity. © The Authors.Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Organic Photovoltaic Morphology

Collins

Bokel

DeLongchamp

2014

Organic Photovoltaics

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Structure Formation in Low-Bandgap Polymer:Fullerene Solar Cell Blends in the Course of Solvent Evaporation

Cited by 26 publications

References 37 publications

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

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

Modeling approach to derive the anisotropic complex refractive index of polymer:fullerene blends for organic solar cells utilizing spectroscopic ellipsometry

Organic Photovoltaic Morphology

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