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Flow-enhanced solution printing of all-polymer solar cells.

Diao Y, Zhou Y, Kurosawa T, Shaw L, Wang C, Park S, Guo Y, Reinspach JA, Gu K, Gu X, Tee BC, Pang C, Yan H, Zhao D, Toney MF, Mannsfeld SC, Bao Z - Nat Commun (2015)

Bottom Line: Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes.The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation.We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA [2] Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.

ABSTRACT
Morphology control of solution coated solar cell materials presents a key challenge limiting their device performance and commercial viability. Here we present a new concept for controlling phase separation during solution printing using an all-polymer bulk heterojunction solar cell as a model system. The key aspect of our method lies in the design of fluid flow using a microstructured printing blade, on the basis of the hypothesis of flow-induced polymer crystallization. Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes. The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation. We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.

No MeSH data available.


Related in: MedlinePlus

Characterization of phase-separated morphology in blend thin films via RSoXS.(a) Two-dimensional scattering images of reference versus FLUENCE films prepared at 25 μm s−1. The intensity is plotted in log scale, with white, brown, yellow, green ranging from high to low intensities. (b) Integrated intensity profiles of reference versus FLUENCE films prepared at various printing speeds. Data corresponding to 100 μm s−1 printing speeds closely resemble those at 75 μm s−1 and are therefore omitted. To compare the scattering anisotropy, intensity from the vertical sector (parallel to the beam polarization direction) is compared with that from the horizontal sector (perpendicular to the beam polarization direction) and the circular average. The vertical (red) and horizontal (green) sectors correspond to the highlighted regions in figure (a). (c) Radius of gyration from Guinier analysis assuming spherical domains. Rg is calculated by fitting the scattering data with I(q)=I0 exp(−q2Rg2/3). The error bars displayed were calculated from s.e. of the fitted parameter Rg. The fitted Rg values are summarized in Supplementary Table 2. The analysis was performed over a q range of 0.001–0.007 Å−1. Beyond this range, poor linearity was found in ln(I) versus q2 plot. Due to this poor linearity and the weak scattering intensity, the higher q feature is not quantitatively analysed but is instead illustrated schematically in d. The corresponding Iq2 versus q plots (vertical sector) are shown in Supplementary Fig. 4. (d) Schematic illustrating the possible in-plane morphology. The schematic is simplified, and the domain connectivity is not shown. The blue medium denotes the amorphous electron-acceptor polymer, P(TP). The red domains represent electron donor PII-tT-PS5, forming amorphous (shown without red bars) and semicrystalline domains (with red bars) The semicystalline domains are not crystallites but are likely aggregates of crystallites, possibly separated by small amorphous regions.
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f3: Characterization of phase-separated morphology in blend thin films via RSoXS.(a) Two-dimensional scattering images of reference versus FLUENCE films prepared at 25 μm s−1. The intensity is plotted in log scale, with white, brown, yellow, green ranging from high to low intensities. (b) Integrated intensity profiles of reference versus FLUENCE films prepared at various printing speeds. Data corresponding to 100 μm s−1 printing speeds closely resemble those at 75 μm s−1 and are therefore omitted. To compare the scattering anisotropy, intensity from the vertical sector (parallel to the beam polarization direction) is compared with that from the horizontal sector (perpendicular to the beam polarization direction) and the circular average. The vertical (red) and horizontal (green) sectors correspond to the highlighted regions in figure (a). (c) Radius of gyration from Guinier analysis assuming spherical domains. Rg is calculated by fitting the scattering data with I(q)=I0 exp(−q2Rg2/3). The error bars displayed were calculated from s.e. of the fitted parameter Rg. The fitted Rg values are summarized in Supplementary Table 2. The analysis was performed over a q range of 0.001–0.007 Å−1. Beyond this range, poor linearity was found in ln(I) versus q2 plot. Due to this poor linearity and the weak scattering intensity, the higher q feature is not quantitatively analysed but is instead illustrated schematically in d. The corresponding Iq2 versus q plots (vertical sector) are shown in Supplementary Fig. 4. (d) Schematic illustrating the possible in-plane morphology. The schematic is simplified, and the domain connectivity is not shown. The blue medium denotes the amorphous electron-acceptor polymer, P(TP). The red domains represent electron donor PII-tT-PS5, forming amorphous (shown without red bars) and semicrystalline domains (with red bars) The semicystalline domains are not crystallites but are likely aggregates of crystallites, possibly separated by small amorphous regions.

Mentions: We next characterized the domain size of the FLUENCE-printed blend films compared with the reference films to understand how our flow design impacts the phase separation. Unlike polymer-fullerene solar cells, small angle X-ray scattering based on hard X-rays is not suitable for characterizing all-polymer BHJ solar cells, due to the low contrast in electron densities between two polymer domains of similar atomic compositions and densities. Thus, we employed resonant soft X-ray scattering (RSoXS) with polarized light, where scattering contrast can be enhanced by tuning the X-ray energy through the aromatic C1s→π* resonance as opposed to the plain electron density differences ‘seen' by X-rays at harder (keV) energies16596061. The use of polarized X-rays offer sensitivity to local molecular orientation due to the anisotropic nature of molecular orbitals involved in the resonant electronic transitions. RSoXS obtained at an off-resonant energy of 270 eV did not yield scattering intensities above the background (other than speckles from surface roughness), whereas at a resonant energy of 283.5 eV, markedly different scattering profiles emerged as seen by comparing FLUENCE-printed films with the reference films prepared at the same conditions (Fig. 3, Supplementary Fig. 4). At low printing speeds, the application of FLUENCE substantially enhanced the scattering anisotropy when comparing the scattering profiles parallel and perpendicular to the beam polarization direction (Fig. 3a,b). Such anisotropy is insensitive to sample in-plane rotation, indicating that the polymer chains have local correlation in their orientation alignment (over tens of nanometres), but are globally isotropic. In the reference films, two characteristic length scales were revealed, one isotropic (low q) and the other anisotropic (high q). In comparison, FLUENCE-printed films exhibited one dominant length scale with a broad distribution and anisotropic scattering profile throughout the investigated q range. At the same time, the dominant scattering feature shifted to higher q. At high printing speeds, the isotropic scattering features diminished in the reference films and the impact of FLUENCE became less obvious other than modestly shifting the scattering feature to higher q (Fig. 3).


Flow-enhanced solution printing of all-polymer solar cells.

Diao Y, Zhou Y, Kurosawa T, Shaw L, Wang C, Park S, Guo Y, Reinspach JA, Gu K, Gu X, Tee BC, Pang C, Yan H, Zhao D, Toney MF, Mannsfeld SC, Bao Z - Nat Commun (2015)

Characterization of phase-separated morphology in blend thin films via RSoXS.(a) Two-dimensional scattering images of reference versus FLUENCE films prepared at 25 μm s−1. The intensity is plotted in log scale, with white, brown, yellow, green ranging from high to low intensities. (b) Integrated intensity profiles of reference versus FLUENCE films prepared at various printing speeds. Data corresponding to 100 μm s−1 printing speeds closely resemble those at 75 μm s−1 and are therefore omitted. To compare the scattering anisotropy, intensity from the vertical sector (parallel to the beam polarization direction) is compared with that from the horizontal sector (perpendicular to the beam polarization direction) and the circular average. The vertical (red) and horizontal (green) sectors correspond to the highlighted regions in figure (a). (c) Radius of gyration from Guinier analysis assuming spherical domains. Rg is calculated by fitting the scattering data with I(q)=I0 exp(−q2Rg2/3). The error bars displayed were calculated from s.e. of the fitted parameter Rg. The fitted Rg values are summarized in Supplementary Table 2. The analysis was performed over a q range of 0.001–0.007 Å−1. Beyond this range, poor linearity was found in ln(I) versus q2 plot. Due to this poor linearity and the weak scattering intensity, the higher q feature is not quantitatively analysed but is instead illustrated schematically in d. The corresponding Iq2 versus q plots (vertical sector) are shown in Supplementary Fig. 4. (d) Schematic illustrating the possible in-plane morphology. The schematic is simplified, and the domain connectivity is not shown. The blue medium denotes the amorphous electron-acceptor polymer, P(TP). The red domains represent electron donor PII-tT-PS5, forming amorphous (shown without red bars) and semicrystalline domains (with red bars) The semicystalline domains are not crystallites but are likely aggregates of crystallites, possibly separated by small amorphous regions.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4557117&req=5

f3: Characterization of phase-separated morphology in blend thin films via RSoXS.(a) Two-dimensional scattering images of reference versus FLUENCE films prepared at 25 μm s−1. The intensity is plotted in log scale, with white, brown, yellow, green ranging from high to low intensities. (b) Integrated intensity profiles of reference versus FLUENCE films prepared at various printing speeds. Data corresponding to 100 μm s−1 printing speeds closely resemble those at 75 μm s−1 and are therefore omitted. To compare the scattering anisotropy, intensity from the vertical sector (parallel to the beam polarization direction) is compared with that from the horizontal sector (perpendicular to the beam polarization direction) and the circular average. The vertical (red) and horizontal (green) sectors correspond to the highlighted regions in figure (a). (c) Radius of gyration from Guinier analysis assuming spherical domains. Rg is calculated by fitting the scattering data with I(q)=I0 exp(−q2Rg2/3). The error bars displayed were calculated from s.e. of the fitted parameter Rg. The fitted Rg values are summarized in Supplementary Table 2. The analysis was performed over a q range of 0.001–0.007 Å−1. Beyond this range, poor linearity was found in ln(I) versus q2 plot. Due to this poor linearity and the weak scattering intensity, the higher q feature is not quantitatively analysed but is instead illustrated schematically in d. The corresponding Iq2 versus q plots (vertical sector) are shown in Supplementary Fig. 4. (d) Schematic illustrating the possible in-plane morphology. The schematic is simplified, and the domain connectivity is not shown. The blue medium denotes the amorphous electron-acceptor polymer, P(TP). The red domains represent electron donor PII-tT-PS5, forming amorphous (shown without red bars) and semicrystalline domains (with red bars) The semicystalline domains are not crystallites but are likely aggregates of crystallites, possibly separated by small amorphous regions.
Mentions: We next characterized the domain size of the FLUENCE-printed blend films compared with the reference films to understand how our flow design impacts the phase separation. Unlike polymer-fullerene solar cells, small angle X-ray scattering based on hard X-rays is not suitable for characterizing all-polymer BHJ solar cells, due to the low contrast in electron densities between two polymer domains of similar atomic compositions and densities. Thus, we employed resonant soft X-ray scattering (RSoXS) with polarized light, where scattering contrast can be enhanced by tuning the X-ray energy through the aromatic C1s→π* resonance as opposed to the plain electron density differences ‘seen' by X-rays at harder (keV) energies16596061. The use of polarized X-rays offer sensitivity to local molecular orientation due to the anisotropic nature of molecular orbitals involved in the resonant electronic transitions. RSoXS obtained at an off-resonant energy of 270 eV did not yield scattering intensities above the background (other than speckles from surface roughness), whereas at a resonant energy of 283.5 eV, markedly different scattering profiles emerged as seen by comparing FLUENCE-printed films with the reference films prepared at the same conditions (Fig. 3, Supplementary Fig. 4). At low printing speeds, the application of FLUENCE substantially enhanced the scattering anisotropy when comparing the scattering profiles parallel and perpendicular to the beam polarization direction (Fig. 3a,b). Such anisotropy is insensitive to sample in-plane rotation, indicating that the polymer chains have local correlation in their orientation alignment (over tens of nanometres), but are globally isotropic. In the reference films, two characteristic length scales were revealed, one isotropic (low q) and the other anisotropic (high q). In comparison, FLUENCE-printed films exhibited one dominant length scale with a broad distribution and anisotropic scattering profile throughout the investigated q range. At the same time, the dominant scattering feature shifted to higher q. At high printing speeds, the isotropic scattering features diminished in the reference films and the impact of FLUENCE became less obvious other than modestly shifting the scattering feature to higher q (Fig. 3).

Bottom Line: Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes.The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation.We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA [2] Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.

ABSTRACT
Morphology control of solution coated solar cell materials presents a key challenge limiting their device performance and commercial viability. Here we present a new concept for controlling phase separation during solution printing using an all-polymer bulk heterojunction solar cell as a model system. The key aspect of our method lies in the design of fluid flow using a microstructured printing blade, on the basis of the hypothesis of flow-induced polymer crystallization. Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes. The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation. We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.

No MeSH data available.


Related in: MedlinePlus