Correlation between morphology and performance of low bandgap oligothiophene:C60 mixed heterojunctions in organic solar cells

Wynands, David; Levichkova, Marieta; Riede, Moritz; Pfeiffer, Martin; Baeuerle, Peter; Rentenberger, Rosina; Denner, Paul; Leo, Karl

doi:10.1063/1.3271407

Cited by 58 publications

(36 citation statements)

References 28 publications

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“…Similar behavior was observed for oligothiophene:C 60 mixtures. [242] Post-growth heat treatment may also be a route for obtaining an increased domain size and crystal order in phase separated bulk heterostructures. [90,104] Phase separation in thin films was also demonstrated for mixtures of PEN:PEN-quinone.…”

Section: Phase Separation In A:b Systemsmentioning

confidence: 99%

Organic–Organic Heterostructures: Concepts and Applications

2012

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We review basic concepts as well as recent examples and applications of organic-organic heterostructures. We organize the different types of heterostructures according to material A deposited on material B (A/B), A co-deposited with B (A:B), heterostructures in the monolayer regime including nanostructuring concepts and systems involving self-assembled monolayers, as well as various other architectures, including superlattices. While most examples are related to small-molecule organic semiconductors, many of the ideas can be applied to other systems. The central theme is growth and structure as well as optical and electronic properties. Finally, we comment on implications for device applications.

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Section: Phase Separation In A:b Systemsmentioning

confidence: 99%

Organic–Organic Heterostructures: Concepts and Applications

2012

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“…Whilst the shortcircuit current density ( J SC ) of OPV devices can be optimized through morphology control, [ 1 ] intermixing, [ 2 , 3 ] nanostructuring [ 4 ] or templating [ 5 ] amongst other techniques, the opencircuit voltage ( V OC ) is critically dependent on the choice of photoactive materials. The relative abundance of suitable commercially available materials has led to a wealth of reports on optimization of the donor layer; [ 6 , 7 ] however the same is not true for the acceptor layer, with most work focusing on the ubiquitous fullerenes.…”

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confidence: 99%

Halogenated Boron Subphthalocyanines as Light Harvesting Electron Acceptors in Organic Photovoltaics

Sullivan

Duraud

Hancox

et al. 2011

Advanced Energy Materials

152

165

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The fi eld of organic photovoltaics (OPVs) is attracting enormous interest due to its promise of providing a low-cost, easily processable technology for energy generation. Whilst the shortcircuit current density ( J SC ) of OPV devices can be optimized through morphology control, [ 1 ] intermixing, [ 2 , 3 ] nanostructuring [ 4 ] or templating [ 5 ] amongst other techniques, the opencircuit voltage ( V OC ) is critically dependent on the choice of photoactive materials. The relative abundance of suitable commercially available materials has led to a wealth of reports on optimization of the donor layer; [ 6 , 7 ] however the same is not true for the acceptor layer, with most work focusing on the ubiquitous fullerenes. Whilst fullerenes are undoubtedly effi cient electron transport materials, this class of acceptor material has inherent issues with long-term stability [ 8 , 9 ] and relatively low bandgaps which limit the maximum obtainable V OC in single heterojunction systems. [ 10 ] Overcoming these issues by use of alternative acceptor materials, whilst maintaining or improving overall effi ciencies, is an important challenge in the OPV fi eld.Initially, the V OC in OPVs was believed to be primarily limited by the work function difference between the two electrodes, however, it has since become clear that the difference in energy between the highest occupied molecular orbital (HOMO) of the donor (D) and the lowest unoccupied molecular orbital (LUMO) of the acceptor (A), i.e. the interface gap ( I G ), is the primary determinant of the maximum V OC obtained. [ 6 , 11 ] Importantly, the frontier orbital energies of organic materials can be readily tuned through introduction of electron-donating or electron-withdrawing substituents. For example, halogenation of conjugated molecules has been shown to lower the HOMO and LUMO levels with respect to the vacuum level whilst having only a small effect on other electronic properties such as the bandgap, or the position of the Fermi level within the bandgap. [ 12 , 13 ] As an example of the extent of modifi cation possible by this method, complete fl uorination of copper phthalocyanine (CuPc) to its hexadecafl uoro derivative (F 16 CuPc) results in a shift of the HOMO level by over 1 eV. [ 14 ] The D/A heterojunction system of boron subphthalocyanine chloride (SubPc)/fullerene (C 60 ) is amongst the current fi eld-leaders for single small molecule heterojunction devices both in terms of V OC ( ∼ 1.1 V) and overall power conversion effi ciency ( PCE ∼ 3%). [ 15 , 16 ] However, consideration of the interfacial energetics of this system reveals that C 60 is far from optimal as the acceptor (vide infra). In this communication, we report the synthesis of several new selectively chlorinated and fl uorinated SubPcs, and demonstrate that effi cient OPV devices can be constructed using these materials as electron acceptors. Moreover, it is shown that peripheral halogenation can be used to maximize the interface gap, and hence the V OC obtained. As well as a remarkably high V ...

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“…However, the benefits (and necessity) of controlling and tuning the mor phology are the same for both technologies. For vacuum processed OSC, it has been recently shown how the mor phology of single layers and bulk heterojunctions between donor and acceptor can be improved by heating the sub strate during deposition [9,10,11]. Higher substrate tem peratures facilitate the aggregation of molecules of the same type.…”

Section: Morphology Optimizationmentioning

confidence: 98%