The study of polythiophene/water interfaces by sum-frequency generation spectroscopy and molecular dynamics simulations

Bellani, Sebastiano; Porro, M.; Caddeo, Claudia; Saba, Maria Ilenia; Miranda, Paulo B.; Mattoni, Alessandro; Lanzani, Guglielmo; Antognazza, Maria Rosa

doi:10.1039/c5tb00388a

Cited by 21 publications

(22 citation statements)

References 97 publications

(174 reference statements)

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“…The polymer bulk model was built as in refs. (see the Supporting Information). In Figure a (right panel) it is reported the stick and balls representation of water/PS atomistic models and the corresponding stationary cross section (obtained after a few nanoseconds).…”

Section: Resultsmentioning

confidence: 99%

Hydrophilicity and Water Contact Angle on Methylammonium Lead Iodide

Caddeo

Marongiu

Meloni

et al. 2018

Adv Materials Inter

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and by relating its value to the liquidsurface adhesion: the larger the adhesion, the smaller the contact angle. [1] Contact angle measurements have become accordingly a powerful yet cheap technique to quantify the water interaction with solid surfaces, a problem of huge technological importance in fluid dynamics, [2] aerospace engineering, [3] biology, [4] surface chemistry, [5] textile, [6] and materials science. [7] In photovoltaics, the interaction of water with surfaces is of great importance for example for organic and hybrid solar cells that are sensitive to humid conditions. This is the case of methylammonium lead iodide (CH 3 NH 3 PbI 3 or MAPI) which is at the core of the nowadays most efficient hybrid-based solar technology (with 23% maximum power conversion efficiencies [8][9][10][11] ) and which has potential applications also in the fields of optoelectronics, [12,13] lasing, [14][15][16][17][18] photocatalysis, [19] and thermoelectricity. [20][21][22] The interaction of MAPI with water is a major concern for such technology as it drives degradation in humid air and full decomposition in liquid water. [23][24][25] Accordingly, there is an increasing number of research items focusing on increasing the hydrophobicity of MAPI via, e.g., surface functionalization. In this context, contact angle measurements have been performed on pristine and hydrophobized films to assess their wettability. [26][27][28] Measurements of the contact angle of water on hybrid perovskites and, more in general, on soluble or transforming surfaces is challenging. If the substrate degrades, several nonequilibrium phenomena must be taken into account such as the solubilization and phase transformations of the solid. This led to ambiguous results on MAPI, with a contact angle that strongly depends on the time of measurement, [26][27][28] calling for a detailed microscopic investigation at the origin of the variability of the measured CA.Here, we combine molecular dynamics (MD) simulations with millisecond contact angle-measurements. We show that finite temperature MD simulations can reproduce experimental contact angles of water in a good agreement with the Young-Dupré (YD) continuum relation between liquid-solid adhesion and contact angle, and we explain the high CA value measured for water on MAPI as the result of the interaction of water with degraded superficial layers at the water/perovskite interface.Surface properties are often assessed with measurements of the contact angle of a water drop. The process is however flawed for the very important class of hybrid perovskite materials, extensively employed in solar cells and optoelectronics research, because they are water soluble and their surface degrades during contact angle measurements. While hybrid perovskites are considered to be highly hydrophilic, a contact angle with water of 83° can be measured, as if they were almost hydrophobic. By combining experiments and simulations, the actual value is explained as the result of the interaction of water with degraded superficial...

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Section: Resultsmentioning

confidence: 99%

Hydrophilicity and Water Contact Angle on Methylammonium Lead Iodide

Caddeo

Marongiu

Meloni

et al. 2018

Adv Materials Inter

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“…The systems were carefully equilibrated by 10 ns long constant pressure and constant temperature annealing (NPT) at room conditions, during which anisotropic volume fluctuations were allowed. In fact, polymer systems are known to have a complex configurational landscape that requires full relaxation and a suitable sampling of the configurational space . Examples of molecular distribution inside the polymer blend at three different fullerene concentrations (i.e., mass ratios) are reported in Figure 3 a.…”

Section: Resultsmentioning

confidence: 99%

“…The VMD 1.9 molecular visualization program has been used to analyze the trajectories. [54] The PTB7 bulk consists of 20 regioregular PTB7 chains of length ≈12 nanometer and periodically replicated along the backbone to mimic an infinite chain. Equilibration at room temperature and pressure was obtained by annealing by the Langevin thermostat and barostat [71] (constant pressure constant temperature NPT ensemble) with anisotropic cell fluctuations for 1 ns.…”

Section: Methodsmentioning

confidence: 99%

“…In fact, polymer systems are known to have a complex configurational landscape that requires full relaxation and a suitable sampling of the configurational space. [51,54] Examples of molecular distribution inside the polymer blend at three different fullerene concentrations (i.e., mass ratios) are reported in Figure 3a. A rich statistics of configurations was obtained in this way enabling calculation of the energy as a function of the fullerene concentration (see additional details in the Supporting Information).…”

Section: Thermal Stability Of Ptb7 Blendsmentioning

confidence: 99%

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Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

Dkhil

Pfannmöller

Saba

et al. 2016

Advanced Energy Materials

105

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The use of fullerene as acceptor limits the thermal stability of organic solar cells at high temperatures as their diffusion inside the donor leads to phase separation via Ostwald ripening. Here it is reported that fullerene diffusion is fully suppressed at temperatures up to 140 °C in bulk heterojunctions based on the benzodithiophene‐based polymer (the poly[[4,8‐bis[(2‐ethylhexyl)oxy]‐benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3,4‐b]thiophenediyl]], (PTB7) in combination with the fullerene derivative [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC70BM). The blend stability is found independently of the presence of diiodooctane (DIO) used to optimize nanostructuration and in contrast to PTB7 blends using the smaller fullerene derivative PC70BM. The unprecedented thermal stability of PTB7:PC70BM layers is addressed to local minima in the mixing enthalpy of the blend forming stable phases that inhibit fullerene diffusion. Importantly, although the nanoscale morphology of DIO processed blends is thermally stable, corresponding devices show strong performance losses under thermal stress. Only by the use of a high temperature annealing step removing residual DIO from the device, remarkably stable high efficiency solar cells with performance losses less than 10% after a continuous annealing at 140 °C over 3 days are obtained. These results pave the way toward high temperature stable polymer solar cells using fullerene acceptors.

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“…Rigid bonds conditions were applied for the hydrogens and the atoms to which they are bonded. The VMD 1.9 molecular visualizationprogram has been used to analyze the trajectories 55,56. The PTB7 bulk consists of 20 regioregular PTB7 chains of length ≈ 12 nm and periodically replicated along the backbone to mimic an infinite chain.…”

mentioning

confidence: 99%

Direct Correlation of Nanoscale Morphology and Device Performance to Study Photocurrent Generation in Donor-Enriched Phases of Polymer Solar Cells

Dkhil

Perkhun

Luo

et al. 2020

ACS Appl. Mater. Interfaces

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The nanoscale morphology of polymer blends is a key parameter to reach high efficiency in bulk heterojunction solar cells. Thereby, research typically focuses on optimal blend morphologies while studying non-optimized blends may give insight into blend design that can be more robust against morphology defects. Here we focus on the direct correlation of morphology and device performance of PTB7:PC71BM bulk heterojunction (BHJ) blends processed without additive in different donor:acceptor weight ratios. We show that while blends of a 1:1.5 ratio are composed of large donor enriched and fullerene domains beyond exciton diffusion length, reducing the ratio below 1:0.5 leads to blends composed purely of polymer enriched domains. Importantly photocurrent density in such blends can reach values between 45 to 60% of those reached of fully optimized blend using additives. We provide here a direct visual evidence that fullerenes in the donor enriched domains are not distributed homogeneously but fluctuate locally. To this end, we performed compositional nanoscale morphology analysis of the blend using spectroscopic imaging of low energy-loss electrons in the transmission electron microscope. Charge transport measurement in combination with molecular dynamics simulations show that the fullerene sub-structures inside the polymer phase generate efficient electron transport in the polymer enriched phase. Furthermore, we show that the formation of densely 3 packed regions of fullerene inside the polymer phase is driven by the PTB7:PC71BM enthalpy of mixing. The occurrence of such a nanoscale network of fullerene clusters leads to a reduction of electron trap states and thus efficient extraction of photocurrent inside the polymer domain. Suitable tuning of the polymer acceptor interaction can thus introduce acceptor sub-networks in polymer enriched phases improving the tolerance for high efficiency BHJ towards morphological defects such as donor enriched domains exceeding exciton diffusion length.

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The study of polythiophene/water interfaces by sum-frequency generation spectroscopy and molecular dynamics simulations

Cited by 21 publications

References 97 publications

Hydrophilicity and Water Contact Angle on Methylammonium Lead Iodide

Hydrophilicity and Water Contact Angle on Methylammonium Lead Iodide

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

Direct Correlation of Nanoscale Morphology and Device Performance to Study Photocurrent Generation in Donor-Enriched Phases of Polymer Solar Cells

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