Evolution of vertical phase separation in P3HT:PCBM thin films induced by thermal annealing

Karagiannidis, Panagiotis; Georgiou, D.; Pitsalidis, Charalampos; Laskarakis, A.; Logothetidis, S.

doi:10.1016/j.matchemphys.2011.06.007

Cited by 106 publications

(93 citation statements)

References 53 publications

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“…11b) show improved absorption and pronounced shoulders at 605 nm as compared to films annealed in air. Karagiannidis et al [46] demonstrated that the extinction coefficient of the P3HT:PCBM film increases with annealing time. It is of interest to note that the optical absorption spectrum related to PCBM is minimised for the substrate annealed films (Fig.…”

Section: Spectroscopic Ellipsometrymentioning

confidence: 99%

Comparative study: the effect of annealing conditions on the properties of P3HT:PCBM blends

et al. 2012

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This paper presents a detailed study on the role of various annealing treatments on organic poly(3-hexylthiophene) and [6]-phenyl-C 61 -butyric acid methyl ester blends under different experimental conditions. A combination of analytical tools is used to study the alteration of the phase separation, structure and photovoltaic properties of the P3HT:PCBM blend during the annealing process. Results showed that the thermal annealing yields PCBM ''needle-like'' crystals and that prolonged heat treatment leads to extensive phase separation, as demonstrated by the growth in the size and quantity of PCBM crystals. The substrate annealing method demonstrated an optimal morphology by eradicating and suppressing the formation of fullerene clusters across the film, resulting in longer P3HT fibrils with smaller diameter. Improved optical constants, PL quenching and a decrease in the P3HT optical bad-gap were demonstrated for the substrate annealed films due to the limited diffusion of the PCBM molecules. An effective strategy for determining an optimized morphology through substrate annealing treatment is therefore revealed for improved device efficiency. IntroductionOrganic photovoltaic (OPV) solar cells have attracted significant attention due to their great potential for large-area, light-weight, flexible, and low-cost devices [1][2][3][4]. Recently, OPV research has been dominated by the poly(3-hexylthiophene):[6]-phenyl C 61 -butyric acid methyl ester (P3HT: PCBM) blend reaching power conversion efficiencies (PCEs) of 5-7 % [5,6]. Most recently a record PCE of about 8.13 and 8.5 % has been reported [7, 8]. Despite recent achievements, improvement in PCEs, stability and lifetime of the devices are necessary before organic solar cells become commercially viable [9][10][11]. The PCE of the solar cells based on the P3HT/fullerene system depends strongly on the processing conditions [12] and can be improved by increasing the crystalline content of the P3HT. Different approaches have been suggested for the optimization of the morphology, such as thermal annealing [5,6,[13][14][15]

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Section: Spectroscopic Ellipsometrymentioning

confidence: 99%

Comparative study: the effect of annealing conditions on the properties of P3HT:PCBM blends

et al. 2012

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“…The effect of vertical stratification of P3HT:PCBM blends [18][19][20][21] can be ignored as the film is only ∼100 nm thick; 2 orders of magnitude smaller than the lateral diffusion which extends over ∼10 -20 µm. Figure 1(b) shows the 1-D perpendicular PCBM composition profile from the centre of the phase segregated region.…”

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confidence: 99%

Molecular versus crystallite PCBM diffusion in P3HT:PCBM blends

Berriman¹,

Holdsworth²,

Zhou³

et al. 2015

AIP Advances

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The diffusion of PCBM in P3HT:PCBM blend films has been investigated using multi-wavelength scanning absorption microscopy (MWSAM). By studying the depletion of PCBM in the vicinity of the phase segregated PCBM-rich regions that form upon thermal annealing, we are able to measure the diffusion constant and activation energy for PCBM diffusion in P3HT:PCBM blend films. The measured kinetic parameters are consistent with the diffusion of nanoscale PCBM crystallites rather than molecular PCBM. We show that the presence of two distinct diffusion processes in these blend materials provides an explanation for the large differences that have been reported for PCBM diffusion in P3HT:PCBM blends. This insight allows us to develop a unified model for PCBM mass transport in these materials.

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“…25 Such models were recently utilized to determine the vertical gradient in the active layer of OSCs 13,25 and to investigate the shape of [6,6]-phenyl C 61 -butyric acid methyl ester (PC 61 BM) inclusions in poly(3-hexylthiophene-2,5-diyl) (P3HT) solar cells. 26 In this work, we present a modeling approach for spectroscopic ellipsometry (SE) data analysis, which facilitates the determination of the complex refractive indices of various polymer:fullerene blends.…”

Section: Introductionmentioning

confidence: 99%

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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Evolution of vertical phase separation in P3HT:PCBM thin films induced by thermal annealing

Cited by 106 publications

References 53 publications

Comparative study: the effect of annealing conditions on the properties of P3HT:PCBM blends

Comparative study: the effect of annealing conditions on the properties of P3HT:PCBM blends

Molecular versus crystallite PCBM diffusion in P3HT:PCBM blends

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

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