Pump‐Probe Spectroscopy in Organic Semiconductors: Monitoring Fundamental Processes of Relevance in Optoelectronics

Cabanillas‐González, Juan; Grancini, Giulia; Lanzani, Guglielmo

doi:10.1002/adma.201102015

Cited by 144 publications

(134 citation statements)

References 115 publications

(89 reference statements)

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“…In this work, we will assess the photoinduced dynamics of the [SQB] n polymer in two different solutions, in DCM where predominantly stretched polymer chains prevail, and in DMF where, besides stretched sections, the polymer possesses mainly helix sections. By transient absorption pump-probe spectroscopy 83 we will show that the dynamics are significantly different in these two solvents which can be traced back to the different superstructure. Finally, support for the interpretation is given by coherent two-dimensional (2D) electronic spectroscopy, as it separates signal contributions into excitation and detection energies.…”

Section: Introductionmentioning

confidence: 98%

Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back

et al. 2015

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We provide a joint experimental and theoretical study of squaraine polymers in solution. The absorption spectra show evidence that two different conformations are present in the polymer: a helix and a zigzag structure. This unique situation allows investigating ultrafast energy-transfer processes between different structural segments within a single polymer chain in solution. The understanding of the underlying dynamics is of fundamental importance for the development of novel materials for light-harvesting and optoelectronic applications. Here, we combine femtosecond transient absorption spectroscopy with time-resolved 2D electronic spectroscopy in order to demonstrate that ultrafast energy transfer within the squaraine polymer chains proceeds from initially excited helix segments to zigzag segments or vice versa, depending on the solvent as well as on the excitation wavenumber. These observations contrast other conjugated polymers such as MEH-PPV where much slower intrachain energy transfer was reported. The reason for the very fast energy transfer in squaraine polymers is most likely a close matching of the density of states between donor and acceptor polymer segments because of the very small reorganization energy in these cyanine-like chromophores.

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Section: Introductionmentioning

confidence: 98%

Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back

et al. 2015

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“…In an operating solar cell, the bound charge pair states have to dissociate by overcoming the mutual Coulomb attraction between electrons and holes, to form free mobile charges (charge-separated states) that can be extracted as photocurrent. While the dissociation of charge pairs in polymer-fullerene blends has been intensively investigated [6][7][8][9][10][11][12][13][14][15][16] , no consensus has yet been reached on how, when and why carriers separate against their mutual Coulomb attraction, to form free independent charges from bound-charge pair states. A point charge description of the electron and hole of the charge pair state appears to result in a high binding energy that would prevent efficient charge separation.…”

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confidence: 99%

Visualizing charge separation in bulk heterojunction organic solar cells

et al. 2013

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Solar cells based on conjugated polymer and fullerene blends have been developed as a low-cost alternative to silicon. For efficient solar cells, electron-hole pairs must separate into free mobile charges that can be extracted in high yield. We still lack good understanding of how, why and when carriers separate against the Coulomb attraction. Here we visualize the charge separation process in bulk heterojunction solar cells by directly measuring charge carrier drift in a polymer:fullerene blend with ultrafast time resolution. We show that initially only closely separated (o1 nm) charge pairs are created and they separate by several nanometres during the first several picoseconds. Charge pairs overcome Coulomb attraction and form free carriers on a subnanosecond time scale. Numerical simulations complementing the experimental data show that fast three-dimensional charge diffusion within an energetically disordered medium, increasing the entropy of the system, is sufficient to drive the charge separation process.

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“…16 Here, we use femtosecond pump-probe spectroscopy to study fewlayer MoS 2 from liquid exfoliation in water and sodium cholate 17 with different amounts of adsorbed surfactant controlled by a multistep washing protocol. We exploit the sensitivity of the pump-probe signal to the change of the electronic excited state population 18 in order to investigate the effect of the surfactant on the carrier and exciton dynamics of MoS 2 . For different amounts of surfactant, we obtain the same shape and relaxation behavior of the pump-probe spectra.…”

Section: Introductionmentioning

confidence: 99%

Femtosecond spectroscopy on MoS₂flakes from liquid exfoliation: surfactant independent exciton dynamics

et al. 2015

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Abstract. Ionic surfactants, which are widely used to stabilize nanomaterials in dispersions, can drastically alter the nanomaterial's photophysical properties. Here, we use femtosecond optical spectroscopy to study the dynamics of excitons and charges in few-layer flakes of the twodimensional semiconductor MoS 2 . We compare samples obtained via exfoliation in water with different amounts of adsorbed sodium cholate, obtained by repeated washing of the dried flakes. We find that the femtosecond dynamics is remarkably stable against the surfactant adsorption, with a slight increase of the initial exciton quenching occurring during the first few picoseconds as the only appreciable effect.

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Pump‐Probe Spectroscopy in Organic Semiconductors: Monitoring Fundamental Processes of Relevance in Optoelectronics

Cited by 144 publications

References 115 publications

Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back

Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back

Visualizing charge separation in bulk heterojunction organic solar cells

Femtosecond spectroscopy on MoS₂flakes from liquid exfoliation: surfactant independent exciton dynamics

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Pump‐Probe Spectroscopy in Organic Semiconductors: Monitoring Fundamental Processes of Relevance in Optoelectronics

Cited by 144 publications

References 115 publications

Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back

Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back

Visualizing charge separation in bulk heterojunction organic solar cells

Femtosecond spectroscopy on MoS2flakes from liquid exfoliation: surfactant independent exciton dynamics

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Femtosecond spectroscopy on MoS₂flakes from liquid exfoliation: surfactant independent exciton dynamics