Light Harvesting for Organic Photovoltaics

Hedley, Gordon J.; Ruseckas, Arvydas; Samuel, Ifor D. W.

doi:10.1021/acs.chemrev.6b00215

Cited by 490 publications

(439 citation statements)

References 296 publications

(682 reference statements)

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“…[1] In addition, directional exciton transport on the nanoscale is exemplified in a sophisticated manner in the lightharvesting antennas of natural photosynthetic systems which give inspiration for research on artificial counterparts for sun light and energy conversion into "solar fuels". [2][3][4][5] Among the potential candidates for exciton transport, conjugated polymers, organic crystalline films of small molecules, as well as…”

Section: Introductionmentioning

confidence: 99%

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

Brixner

Hildner

Köhler

et al. 2017

Advanced Energy Materials

292

301

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The transport of excitation energy in molecular aggregates is of crucial importance for the function of organic optoelectronic devices and next‐generation solar cells. First, this review summarizes the theoretical background of the nature of the electronically excited states of molecular aggregates. For these systems, the electronic interaction between the monomers leads to the formation of exciton states. This goes along with a shift of the excitation energies and a redistribution of the oscillator strength with respect to the monomers. Next, a brief overview is provided over experimental techniques that allow to study the properties of excitons in molecular aggregates. This includes single‐molecule spectroscopy, coherent two‐dimensional (2D) spectroscopy, and single‐molecule coherent spectroscopy. Finally, examples of molecular aggregates spanning the range from natural systems that act in photosynthesis as light‐harvesting antennas to artificial aggregates built from synthetic chromophores are illustrated.

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Section: Introductionmentioning

confidence: 99%

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

Brixner

Hildner

Köhler

et al. 2017

Advanced Energy Materials

292

301

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“…[1][2][3] Many different techniques have been developed to probe exciton transport; however, each measurement has its own implicit assumptions and constraints. [1][2][3] Many different techniques have been developed to probe exciton transport; however, each measurement has its own implicit assumptions and constraints.…”

Section: Introductionmentioning

confidence: 99%

Decoupling Photocurrent Loss Mechanisms in Photovoltaic Cells Using Complementary Measurements of Exciton Diffusion

Curtin

Holmes

2018

Advanced Energy Materials

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techniques which have been previously applied to extract L D in organic semiconductors. Each of these measurements probes a different stage of the photoconversion process, and by combining these techniques we quantitatively decouple the associated exciton and charge carrier losses as a function of forward bias, providing insight into materials and device properties which limit OPV performance.Photoconversion in OPVs relies on a heterojunction between electron donating and accepting materials and occurs via a series of steps, each characterized by its own efficiency. [1,4] Incident photons are absorbed by the active material with efficiency η A leading to exciton generation. Excitons then diffuse to the dissociating donor-acceptor (D-A) interface with a diffusion efficiency η D . The exciton diffusion length is typically on the order of tens of nanometers, limiting active layer thickness and consequently η A . [2,4,5] At the D-A interface, the offset in molecular orbital energy levels drives exciton dissociation by charge transfer with efficiency η CT , leading to the formation of a Coulombically bound charge transfer (CT) state across the interface. The CT state may be dissociated into a pair of charge carriers with efficiency η CS , or undergo geminate recombination at the interface. Generated free charge carriers may be collected at the electrodes as photocurrent (η FC ) or undergo non-geminate recombination with a carrier of opposite polarity. [6,7] The product of these efficiencies determines the device external quantum efficiency (η EQE ).As a function of forward bias, the values of η D , η CS , and η FC can be reduced due to exciton-and polaron-driven losses. These parasitic loss pathways often result in a steep reduction in the photocurrent (J photo ) as a function of forward bias voltage, leading to low device fill factors that limit the maximum operating power. [6,8] Reductions in η D may result from excitonic losses by exciton-polaron quenching. [9][10][11][12] It has been previously established that there is a direct relationship between the operating voltage and the number of polarons present in an OPV. [13][14][15][16] Therefore, it follows that as the forward bias voltage increases in a device, so does the number of polarons, increasing the likelihood of an exciton being quenched prior to dissociation. [9] Dissociation of the interfacial CT state is assisted by the device built-in field. [8,[17][18][19] However, as the Significant work has been directed at measuring the exciton diffusion length (L D ) in organic semiconductors due to its significance in determining the performance of photovoltaic cells. Several techniques have been developed to measure L D , often probing photoluminescence or charge carrier generation. Interestingly, in this study it is shown that when different techniques are compared, both the diffusive behavior of the exciton and active carrier recombination loss pathways can be decoupled. Here, a planar heterojunction device based on the donor-acceptor pairing of boron subphthal...

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“…[4][5][6] However, they pose a significant challenge for conventional DFT and TDDFT approximations. 7,8 The fundamental reason behind this challenge is that CT excitations involve, by definition, transitions between filled states and empty states with very little spatial overlap.…”

Section: Introductionmentioning

confidence: 99%

Charge transfer excitations from exact and approximate ensemble Kohn-Sham theory

Gould¹,

Pittalis²,

Kronik³

2018

Preprint

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By studying the lowest excitations of an exactly solvable one-dimensional molecular model, we show that components of Kohn-Sham ensembles can be used to describe charge transfers. Furthermore, we compute the approximate excitation energies obtained by using thee exact ensemble densities in the recently formulated ensemble Hartree-exchange theory [Gould and Pittalis, Phys. Rev. Lett. 119, 243001 (2017)]. Remarkably, our results show that triplet excitations are accurately reproduced across a dissociation curve in all cases tested, even in systems where ground state energies are poor due to strong static correlations. Singlet excitations exhibit larger deviations from exact results but are still reproduced semi-quantitatively.

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Light Harvesting for Organic Photovoltaics

Cited by 490 publications

References 296 publications

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

Decoupling Photocurrent Loss Mechanisms in Photovoltaic Cells Using Complementary Measurements of Exciton Diffusion

Charge transfer excitations from exact and approximate ensemble Kohn-Sham theory

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