scholarly journals Origin of Charge Separation at Organic Photovoltaic Heterojunctions: A Mesoscale Quantum Mechanical View

2017 ◽  
Vol 121 (31) ◽  
pp. 16693-16701 ◽  
Author(s):  
Mosè Casalegno ◽  
Raffaele Pastore ◽  
Julien Idé ◽  
Riccardo Po ◽  
Guido Raos
Keyword(s):  
Charge Separation ◽  
Organic Photovoltaic ◽  
Quantum Mechanical

scholarly journals SEPARAZIONE DI CARICA IN MISCELE DI MATERIALI ORGANICI: VALE LA LEGGE DI COULOMB?

2020 ◽  
Author(s):  
Guido Raos
Keyword(s):  
Theoretical Model ◽  
Charge Separation ◽  
Negative Charge ◽  
Charge Carriers ◽  
Organic Photovoltaic ◽  
Quantum Mechanical ◽  
Apparent Contradiction ◽  
Photovoltaic Materials ◽  
Organic Photovoltaic Materials ◽  
Quantum Mechanical Effects

After a brief introduction to organic photovoltaic materials, I discuss the problem of charge separation in these systems. In the best devices, the excitations produced by absorption of a photon can be converted into positive and negative charge carriers (holes and electrons, respectively) with near-100% efficiency. Such efficiencies are apparently at odds with Coulomb’s law, which would lead to change recombination due to their mutual electrostatic attraction. A theoretical model developed within my group overcomes this apparent contradiction, by taking into account quantum mechanical effects such as the delocalization of the charge carriers.

Excitation Transport and Charge Separation in an Organic Photovoltaic Material:  Watching Excitations Diffuse to Interfaces

2008 ◽  
Vol 112 (10) ◽  
pp. 3926-3934 ◽  
Author(s):  
Larry W. Barbour ◽  
Ryan D. Pensack ◽  
Maureen Hegadorn ◽  
Sergei Arzhantsev ◽  
John B. Asbury
Keyword(s):  
Charge Separation ◽  
Organic Photovoltaic ◽  
Photovoltaic Material

scholarly journals Spectroscopic investigation of excitonic and charge photogeneration processes in organic photovoltaic cells

2021 ◽  
Author(s):  
◽  
Joseph Gallaher
Keyword(s):  
Excited States ◽  
Charge Separation ◽  
Transient Absorption ◽  
Mirror Image ◽  
Triplet Exciton ◽  
Organic Photovoltaic ◽  
Charge Generation ◽  
Time Resolved ◽  
Blend Morphology ◽  
Time Resolved Photoluminescence

<p>Organic photovoltaic (OPV) cells show significant promise as a renewable energy resource capable of meeting the world’s large and growing energy needs. Increasing device efficiency is central to achieving an economically viable option for widespread applications. To this end, a better understanding of the structure and dynamics of the electronic excited states is needed. In particular, the mechanism by which excitons (electron-hole pairs) escape their Coulombic attraction and generate photocurrent is yet to be established. In this thesis ultrafast laser spectroscopy, in particular transient absorption and time-resolved photoluminescence, are used to study: exciton relaxation, morphological effects on charge separation, and the pathway leading to triplet exciton states.  In Chapter 3, a series of oligothiophenes are synthesised with well-defined conjugation lengths to act as molecular models of polymer backbone sub-units, and thereby probe exciton relaxation processes. Time-resolved photoluminescence (TRPL) and transient absorption (TA) spectroscopy measurements presented in Chapter 4 reveal emission signatures evolve from a mirror image of absorption - which lacks vibronic structure - towards a spectrally narrower and vibronically structured species on the hundreds of femtosecond to early picosecond timescale. Analysis of this spectral evolution shows that a broad distribution of torsional conformers is driven to rapidly planarize in the excited state, including in solid films. This provides evidence that both torsional relaxation and energy migration could contribute to the non-mirror image absorption-emission spectra observed in polymer thin films.  Recently, long lived TA signatures have been attributed to triplet excited states with the suggested formation pathway being similar to organic light emitting diodes, whereby non-geminate (bimolecular) charge recombination leads to the formation of both singlet and triplet states. Isolated oligothiophenes in solution provide an ideal model system to investigate the role of structural relaxation on triplet exciton formation. Through analysis of TA spectral dynamics in Chapter 5, singlet and triplet exciton populations were tracked. Restriction of the torsional relaxation increased triplet yield suggesting vibrational hot states could drive triplet formation. This model could aid in understanding triplet exciton formation in polymer-based solar cells via spin-mixing instead of non-geminate recombination.  In a series of polymer:fullerene blends, the link between the nature of polymerfullerene intermixing and charge generation pathways was investigated. It is shown in Chapter 6 that free charge generation is most efficient in a 3-phase morphology that features intimately mixed polymer:fullerene regions amongst neat polymer and fullerene phases. Distinct spectroscopic signatures made it possible to determine whether holes occupy disordered or crystalline polymer chains. TA spectral dynamics reveal the migration of holes from intermixed to pure olymer regions in 3-phase morphology blends, which contrasted with observations in 2-phase blends. The energy gradient between the intermixed and phase-pure regions may be sufficient to drive efficient separation of charge pairs initially generated in intermixed regions, with free charges subsequently percolating through these phase-pure domains.  The photophysics of a high performance polymer:polymer blend is studied in Chapter 7 in an effort to elucidate how these blends can rival their polymer:fullerene counterparts. Optical spectroscopy reveals incomplete exciton dissociation and rapid geminate recombination in the blends. This is shown to result from a largely phase-separated morphology with domains greater than the exciton diffusion length. Significant loss of charge carriers on early timescales highlights increasing polymer: polymer solar cell efficiency requires optimizing blend morphology to realise facile charge separation.  Taken together, this thesis presents a valuable spectroscopic insight into the pathway of efficient charge separation and the importance of both blend morphology and polymer structure.</p>

Multiple Charge Separation Pathways in New-Generation Non-Fullerene Acceptors: a Computational Study

2021 ◽  
Author(s):  
Alessandro Landi ◽  
Daniele Padula
Keyword(s):  
Charge Separation ◽  
Computational Study ◽  
Organic Photovoltaic ◽  
Photovoltaic Devices ◽  
Organic Photovoltaic Devices ◽  
New Generation ◽  
Multiple Charge

Non-fullerene acceptors led to outstanding improvements in the efficiency of organic photovoltaic devices, with high promises of further advancements. Several studies have been performed to rationalise their exceptional performances, with...

Does Electron Delocalization Influence Charge Separation at Donor–Acceptor Interfaces in Organic Photovoltaic Cells?

2018 ◽  
Vol 122 (38) ◽  
pp. 21792-21802 ◽  
Author(s):  
Frank-Julian Kahle ◽  
Christina Saller ◽  
Selina Olthof ◽  
Cheng Li ◽  
Jenny Lebert ◽  
...  
Keyword(s):  
Charge Separation ◽  
Photovoltaic Cells ◽  
Organic Photovoltaic ◽  
Electron Delocalization ◽  
Organic Photovoltaic Cells ◽  
Donor Acceptor

Charge Separation from an Intra-Moiety Intermediate State in the High-Performance PM6:Y6 Organic Photovoltaic Blend

2020 ◽  
Vol 142 (29) ◽  
pp. 12751-12759 ◽  
Author(s):  
Rui Wang ◽  
Chunfeng Zhang ◽  
Qian Li ◽  
Zhiguo Zhang ◽  
Xiaoyong Wang ◽  
...  
Keyword(s):  
Intermediate State ◽  
Charge Separation ◽  
High Performance ◽  
Organic Photovoltaic

Charge generation in organic photovoltaics: a review of theory and computation

2016 ◽  
Vol 1 (1) ◽  
pp. 10-24 ◽  
Author(s):  
Kenley M. Pelzer ◽  
Seth B. Darling
Keyword(s):  
Organic Photovoltaics ◽  
Charge Separation ◽  
Photovoltaic Device ◽  
Organic Photovoltaic ◽  
Device Performance ◽  
Exciton Dissociation ◽  
Charge Generation ◽  
Computational Approaches ◽  
Organic Photovoltaic Device ◽  
Donor Acceptor

One of the most important factors in determining organic photovoltaic device performance is the efficiency of exciton dissociation and charge separation at donor/acceptor heterojunctions. This review discusses theoretical and computational approaches to modeling this crucial process of charge generation.

Shining light on supramolecular assemblies

2009 ◽  
Vol 81 (9) ◽  
pp. 1677-1685 ◽  
Author(s):  
Vincent Darcos ◽  
Chih-Hao Huang ◽  
Nathan McClenaghan ◽  
Yann Molard ◽  
James H. R. Tucker ◽  
...  
Keyword(s):  
Charge Separation ◽  
Metal Ion ◽  
Noncovalent Interactions ◽  
Supramolecular Assemblies ◽  
Organic Photovoltaic ◽  
Supramolecular Interactions ◽  
Photovoltaic Devices ◽  
Organic Photovoltaic Devices ◽  
Solid State Devices ◽  
Photoinduced Processes

The organizational effect induced by noncovalent interactions such as hydrogen-bonding (H-B) and metal ion complexation on photoinduced processes is discussed. These include the intermolecular photodimerization of cinnamates, which is shown to occur under topochemical control within the supramolecular assemblies, and the intramolecular photodimerization of a bis-anthracene receptor where photoregulation of the recognition event is achieved. Progress in using supramolecular interactions toward the preparation of assemblies promoting charge separation and charge transport in all-organic photovoltaic devices rests on the preparation of materials that are adapted to the requirements of solid-state devices.

On the role of local charge carrier mobility in the charge separation mechanism of organic photovoltaics

2015 ◽  
Vol 17 (27) ◽  
pp. 17778-17784 ◽  
Author(s):  
Saya Yoshikawa ◽  
Akinori Saeki ◽  
Masahiko Saito ◽  
Itaru Osaka ◽  
Shu Seki
Keyword(s):  
Charge Carrier ◽  
Charge Separation ◽  
Carrier Mobility ◽  
Charge Carrier Mobility ◽  
Transport Processes ◽  
Organic Photovoltaic ◽  
Separation Mechanism ◽  
Geminate Recombination ◽  
Local Charge

Although the charge separation (CS) and transport processes that compete with geminate and non-geminate recombination are commonly regarded as the governing factors of organic photovoltaic (OPV) efficiency, the details of the CS mechanism remain largely unexplored.

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