Charge Generation at Polymer/Metal Oxide Interface: from Molecular Scale Dynamics to Mesoscopic Effects

Kandada, Ajay Ram Srimath; Guarnera, Simone; Tassone, F.; Lanzani, Guglielmo; Petrozza, Annamaria

doi:10.1002/adfm.201303689

Cited by 10 publications

(11 citation statements)

References 31 publications

(45 reference statements)

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“…They are related to the excess of sulfonic acid groups brought in by the PFI and FOS agents along with the electro-negativity of the fluorinated moieties. This is equivalent to negative Burstein shifts induced on the apparent band gap when extra charges are added, for instance through doping, [111][112][113][114] and consistent with the variation of n and k observed for various conjugated molecules when in oxidized or reduced states. [115][116][117] Noticeably, this trend was preserved when the PEDOT:PSS based thin films were covered by the conjugated polymer:PCBM blends (Fig.…”

supporting

confidence: 68%

Enhanced organic solar cells efficiency through electronic and electro-optic effects resulting from charge transfers in polymer hole transport blends

et al. 2016

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 and ‡ These authors contributed equally to this work.We demonstrate that blending fluorinated molecules in PEDOT:PSS hole transport layers (HTL) induces charge transfers which impact on both charge extraction and photogeneration within organic photovoltaic (OPV) devices. OPVs fabricated with modified HTL and two photoactive polymer blends led systematically to power conversion efficiencies (PCE) increases, with PTB7:PC70BM blend exhibiting PCE of ~ 8.3 %, i.e. ~ 15 % increase compared to pristine HTL devices. A reduced device-to-device characteristics variations was also noticed when fluorinated additives were used to modify the PEDOT:PSS. Shading lights onto the effect of HTL fluorination, we show that the morphology of the polymer:PCBM blends remains surprisingly unaffected by the fluorinated HTL surface energy but that, instead, the OPVs are impacted not only by the HTL electronic properties (work function, dipole layer, open circuit voltage, charge transfer dynamic) but also by alteration of the complex refractive indices (photogeneration, short circuit current density, external quantum efficiencies, electro-optic modelling). Both mechanisms find their origin in fluorination induced charge transfers. This work points towards fluorination as a promising strategy toward combining both external quantum efficiency modulation and power conversion efficiency enhancement in OPVs. Charge transfers could also be used more broadly to tune the optical constants and electric field distribution, as well as to reduce interfacial charge recombinations within OPVs. [21][22][23][24][25][26][27][28][29]

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confidence: 68%

Enhanced organic solar cells efficiency through electronic and electro-optic effects resulting from charge transfers in polymer hole transport blends

et al. 2016

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“…III C we could show that mesoporous TiO 2 only has marginal effect on the polymer crystallinity compared to plane glass substrates. This is not in accordance with previous observations by Kandada et al [15]. The authors report a noticeable amount of disorder introduced by the mesoporous surface.…”

Section: Discussioncontrasting

confidence: 95%

“…The similarity of both spectra implies that the inorganic metal oxide does not have a decisive influence on the bulk polymer morphology. Note that this observation does not contradict findings by Kandada et al [15], who report a noticeable amount of disorder introduced by the mesoporous surface, because there is a large dependence on the amount of pore filling, different molecular weights, process conditions, and TiO 2 composition.…”

Section: Uv/visible Absorption and Pl-morphology Investigationsupporting

confidence: 70%

“…This paper addresses this question by comparing three model systems for (1) dye only (DO) photocurrent contribution, (2) exciton dissociation (ED) in the polymer at the dye interface, and (3) FRET of the exciton from the polymer to the dye. A HTM poly(3hexylthiophene) (P3HT) is used due to its widely known and extensively studied properties [11][12][13][14][15]. Furthermore, it is the most widely employed polymeric HTM in hybrid solar cells and thus is well suited to serve as a model HTM.…”

Section: Introductionmentioning

confidence: 99%

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Role of charge separation mechanism and local disorder at hybrid solar cell interfaces

et al. 2015

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Dye-sensitized metal oxide polymer hybrid solar cells deliver a promising basis in organic solar cell development due to many conceptual advantages. Since the power conversion efficiency is still in a noncompetitive state, it has to be understood how the photocurrent contribution can be maximized (i.e., which dye-polymer properties are most beneficial for efficient charge generation in hybrid solar cells). By the comparison of three model systems for hybrid solar cells with TiO 2-dye-polymer interfaces, this paper was aimed at elucidating the role of the exact mechanism of charge generation. In the exciton dissociation (ED) case, an exciton that is generated in the polymer is split at the dye-polymer interface. Alternatively, this exciton can be transferred to the dye via an energy transfer (ET), upon which charge separation occurs between dye and TiO 2. For comparison, the third case is included in which the high lowest unoccupied molecular orbital of the dye does not allow exciton separation or ET from the dye to the polymer, so that the dye only is responsible for charge generation. To separate effects owing to differences in energy levels of the involved materials from the impact of local order and disorder in the polymer close to the interface, this paper further comprises a detailed analysis of the polymer crystallinity based on the H-aggregate model. While the massive impact of the poly(3-hexylthiophene) crystallinity on device function has been outlined for bare metal oxide-polymer interfaces, it has not been considered for hybrid solar cells with dye-sensitized TiO 2. The results presented here indicate that all dye molecules in general influence the polymer morphology, which has to be taken into account for future optimization of hybrid solar cells. Apart from that, it can be suggested that ED on the polymer needs an additional driving force to work efficiently; thus, energy transfer seems to be currently the most promising strategy to increase the polymer photocurrent contribution.

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“…The thickness of a P3HT film is adjusted by spin-casting solutions of varying polymer concentration. This is a commonly used and an appropriate method 16 17 18 for low concentrations, in which the intermolecular interaction in solution is minimal 19 . In general, the lower the concentration, the thinner the polymer film.…”

Section: Resultsmentioning

confidence: 99%

H-aggregate analysis of P3HT thin films-Capability and limitation of photoluminescence and UV/Vis spectroscopy

Ehrenreich

Birkhold

Zimmermann

et al. 2016

Sci Rep

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Polymer morphology and aggregation play an essential role for efficient charge carrier transport and charge separation in polymer-based electronic devices. It is a common method to apply the H-aggregate model to UV/Vis or photoluminescence spectra in order to analyze polymer aggregation. In this work we present strategies to obtain reliable and conclusive information on polymer aggregation and morphology based on the application of an H-aggregate analysis on UV/Vis and photoluminescence spectra. We demonstrate, with P3HT as model system, that thickness dependent reflection behavior can lead to misinterpretation of UV/Vis spectra within the H-aggregate model. Values for the exciton bandwidth can deviate by a factor of two for polymer thicknesses below 150 nm. In contrast, photoluminescence spectra are found to be a reliable basis for characterization of polymer aggregation due to their weaker dependence on the wavelength dependent refractive index of the polymer. We demonstrate this by studying the influence of surface characteristics on polymer aggregation for spin-coated thin-films that are commonly used in organic and hybrid solar cells.

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Charge Generation at Polymer/Metal Oxide Interface: from Molecular Scale Dynamics to Mesoscopic Effects

Cited by 10 publications

References 31 publications

Enhanced organic solar cells efficiency through electronic and electro-optic effects resulting from charge transfers in polymer hole transport blends

Enhanced organic solar cells efficiency through electronic and electro-optic effects resulting from charge transfers in polymer hole transport blends

Role of charge separation mechanism and local disorder at hybrid solar cell interfaces

H-aggregate analysis of P3HT thin films-Capability and limitation of photoluminescence and UV/Vis spectroscopy

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