Charge Carrier Generation and Transport in Different Stoichiometry APFO3:PC61BM Solar Cells

Pranculis, Vytenis; Infahsaeng, Yingyot; Tang, Zheng; Devižis, Andrius; Vithanage, Dimali A.; Ponseca, Carlito S.; Inganäs, Olle; Yartsev, Arkady; Gulbinas, Vidmantas; Sundström, Villy

doi:10.1021/ja503301m

Cited by 32 publications

(45 citation statements)

References 45 publications

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mixture of electron donating and accepting materials-a bulk heterojunction (BHJ). [8] The effect of donor-acceptor mixing (or phase purity) on charge transport has been previously addressed using microstructural characterization, [9,10] steady-state, [11][12][13] and/or timeresolved [14][15][16] mobility measurements on BHJs with a varying donor-acceptor stoichiometry and/or processing conditions. The coexistence of neat and mixed donoracceptor domains is thought to be beneficial as it could provide an energy cascade [4,5] for charge separation, [6,7] followed by charge transport in the neat phases.

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confidence: 99%

Charge Transport in Pure and Mixed Phases in Organic Solar Cells

Melianas

Pranculis

Spoltore

et al. 2017

Advanced Energy Materials

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116

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mixture of electron donating and accepting materials-a bulk heterojunction (BHJ). Such interpenetrating donoracceptor mixtures form complicated multilength scale morphologies, often involving several phases such as ordered/ disordered donor, mixed donor-acceptor and ordered/disordered acceptor. The coexistence of neat and mixed donoracceptor domains is thought to be beneficial as it could provide an energy cascade [4,5] for charge separation, [6,7] followed by charge transport in the neat phases. However, the neat regions may be discontinuous, forcing charges to cross mixed domains multiple times during extraction. If the mixed regions are severely disordered or contain less than the percolation threshold of required material, charge transport is thought to deteriorate significantly, limiting device performance. [8] The effect of donor-acceptor mixing (or phase purity) on charge transport has been previously addressed using microstructural characterization, [9,10] steady-state, [11][12][13] and/or timeresolved [14][15][16] mobility measurements on BHJs with a varying donor-acceptor stoichiometry and/or processing conditions. Although such studies have revealed important trends, they remain mostly semiquantitative-the question of how pure the neat domains have to be and how detrimental domain discontinuities or donor-acceptor mixing are in relation to charge transport kinetics remains to a large extent unanswered. Not knowing which important charge transport features to optimize, limits the development of next generations of organic optoelectronic devices.Here, we address this by measuring photo-generated charge motion from the first hopping events (with sub-picosecond time resolution) to full extraction in complete solar cell devices based on coevaporated bulk heterojunctions of α-sexithiophene (α-6T) and buckminsterfullerene (C 60 ). We carefully vary the molar fraction of α-6T in C 60 from homogeneously diluted (<10% molar), to a point where α-6T begins to form isolated aggregates (>10%-25% molar) or is strongly aggregated (50% molar). We thus vary the distance between isolated α-6T sites and the level of disruption of the C 60 phase in a controlled manner-the α-6T:C 60 system may be viewed as a model for the mixed donor-acceptor phase in OPV. C 60 was chosen as the model acceptor since its use in organic electronics is In organic solar cells continuous donor and acceptor networks are considered necessary for charge extraction, whereas discontinuous neat phases and molecularly mixed donor-acceptor phases are generally regarded as detrimental. However, the impact of different levels of domain continuity, purity, and donor-acceptor mixing on charge transport remains only semiquantitatively described. Here, cosublimed donor-acceptor mixtures, where the distance between the donor sites is varied in a controlled manner from homogeneously diluted donor sites to a continuous donor network are studied. Using transient measurements, spanning from sub-picoseconds to microseconds photogenerated charge motion is measured i...

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confidence: 99%

Charge Transport in Pure and Mixed Phases in Organic Solar Cells

Melianas

Pranculis

Spoltore

et al. 2017

Advanced Energy Materials

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116

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“…Our results are also applicable to small molecule donors and pristine fullerenes. It has been recently experimentally demonstrated that mainly electron motion in PCBM is responsible for the initial evolution of the charge separation process – hole motion is significantly slower51112. Therefore, in our treatment we consider the hole to be immobile.…”

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Role of coherence and delocalization in photo-induced electron transfer at organic interfaces

Abramavicius

Pranculis

Melianas

et al. 2016

Sci Rep

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Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces.

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“…The first report of charge generation in PPV/C 60 blends [21,91] was interpreted as evidence for immediate charge generation, presumably at domains where order was strong enough to allow for formation of delocalized charges. [96] The transients were also studied with THz methods. The responses over the timescale of ps and ns are highly dependent on the materials systems studied.…”

Section: Photogeneration Of Charge In Donor-acceptor Bulk Heterojunctmentioning

confidence: 99%

Organic Photovoltaics over Three Decades

2018

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The development of organic semiconductors for photovoltaic devices, over the last three decades, has led to unexpected performance for an alternative choice of materials to convert sunlight to electricity. New materials and developed concepts have improved the photovoltage in organic photovoltaic devices, where records are now found above 13% power conversion efficiency in sunlight. The author has stayed with the topic of organic materials for energy conversion and energy storage during these three decades, and makes use of the Hall of Fame now built by Advanced Materials, to present his view of the path travelled over this time, including motivations, personalities, and ambitions.

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Charge Carrier Generation and Transport in Different Stoichiometry APFO3:PC61BM Solar Cells

Cited by 32 publications

References 45 publications

Charge Transport in Pure and Mixed Phases in Organic Solar Cells

Charge Transport in Pure and Mixed Phases in Organic Solar Cells

Role of coherence and delocalization in photo-induced electron transfer at organic interfaces

Organic Photovoltaics over Three Decades

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