Subpicosecond photoinduced electron transfer from conjugated polymers to functionalized fullerenes

Kraabel, B.; Hummelen, Jan C.; Vacar, D.; Moses, D.; Sariciftci, Niyazi Serdar; Heeger, Alan J.; Wudl, Fred

doi:10.1063/1.471154

Cited by 173 publications

(110 citation statements)

References 18 publications

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“…The data imply therefore that 1/ ct Ͼ 10 12 ; i.e., electron transfer occurs on the subpicosecond time scale. The ultrafast charge-transfer process was subsequently time resolved (Kraabel et al, 1994(Kraabel et al, , 1996Lanzani et al, 2000); the data directly confirm that charge transfer occurs within a hundred femtoseconds. The photoinduced electron-transfer process serves to sensitize the photoconductivity of the semiconducting polymer (Lee, Yu, et al, 1993).…”

Section: Photoinduced Electron Transfermentioning

confidence: 78%

Nobel Lecture: Semiconducting and metallic polymers: The fourth generation of polymeric materials

2001

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Section: Photoinduced Electron Transfermentioning

confidence: 78%

Nobel Lecture: Semiconducting and metallic polymers: The fourth generation of polymeric materials

2001

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“…This question has been puzzling the PSC community since the birth of PSCs. [24][25][26] There have been different mechanisms proposed to answer this question, with conflicting evidence for different opinions.…”

Section: Introductionmentioning

confidence: 99%

Charge generation in polymer–fullerene bulk-heterojunction solar cells

Gao

Inganäs

2014

Phys. Chem. Chem. Phys.

203

250

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Charge generation in organic solar cells is a fundamental yet heavily debated issue. This article gives a balanced review of different mechanisms proposed to explain efficient charge generation in polymer-fullerene bulk-heterojunction solar cells. We discuss the effect of charge-transfer states, excess energy, external electric field, temperature, disorder of the materials, and delocalisation of the charge carriers on charge generation. Although a general consensus has not been reached yet, recent findings, based on both steady-state and transient measurements, have significantly advanced our understanding of this process.2

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“…Literature reports have estimated that excitons can diffuse only over distances of ∼10 nm. 6,7 If the polymer and fullerene components are phasesegregated on this same length scale, then essentially every exciton can diffuse to within charge-transfer range of a fullerene molecule during its lifetime, resulting in exciton splitting and formation of polaron pairs [8][9][10] with near-unit quantum yield.…”

Section: Introductionmentioning

confidence: 99%

Reappraising the Need for Bulk Heterojunctions in Polymer−Fullerene Photovoltaics: The Role of Carrier Transport in All-Solution-Processed P3HT/PCBM Bilayer Solar Cells

et al. 2009

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The most efficient organic solar cells produced to date are bulk heterojunction (BHJ) photovoltaic devices based on blends of semiconducting polymers such as poly(3-hexylthiophene-2,5-diyl) (P3HT) with fullerene derivatives such as [6,6]-penyl-C 61 -butyric-acid-methyl-ester (PCBM). The need for blending the two components is based on the idea that the exciton diffusion length in polymers like P3HT is only ∼10 nm, so that the polymer and fullerene components must be mixed on this length scale to efficiently split the excitons into charge carriers. In this paper, we show that the BHJ geometry is not necessary for high efficiency, and that all-solution-processed P3HT/PCBM bilayer solar cells can be nearly as efficient as BHJ solar cells fabricated from the same materials. We demonstrate that o-dichlorobenzene (ODCB) and dichloromethane serve nicely as a pair of orthogonal solvents from which sequential layers of P3HT and PCBM, respectively, can be spin-cast. Atomic force microscopy, various optical spectroscopies, and electron microscopy all demonstrate that the act of spin-coating the PCBM overlayer does not affect the morphology of the P3HT underlayer, so that our spin-cast P3HT/PCBM bilayers have a well-defined planar interface. Our fluorescence quenching experiments find that there is still significant exciton splitting in P3HT/PCBM bilayers even when the P3HT layer is quite thick. When we fabricated photovoltaic devices from these bilayers, we obtained photovoltaic power conversion efficiencies in excess of 3.5%. Part of the reason for this high efficiency is that we were able to separately optimize the roles of each component of the bilayer; for example, we found that thermal annealing has relatively little effect on the nature of P3HT layers spin-cast from ODCB, but that it significantly increases the crystallinity and thus the mobility of electrons through PCBM. Because the carriers in bilayer devices are generated at the planar P3HT/PCBM interface, we also were able to systematically vary the distance the carriers have to travel to be extracted at the electrodes by changing the layer thicknesses without altering the bulk mobility of either component or the nature of the interfaces. We found that devices have the best fill-factors when the transit times of electrons and holes through the two layers are roughly balanced. In particular, we found that the most efficient devices are made with P3HT layers that are about four times thicker than the PCBM layers, demonstrating that it is the conduction and the extraction of electrons through the fullerene that ultimately limit the performance of both bilayer and BHJ devices based on the P3HT/ PCBM material combination. Overall, we believe that polymer-fullerene bilayers provide several advantages over BHJ devices, including reduced carrier recombination and a much better degree of control over the properties of the individual components and interfaces during device fabrication.

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Subpicosecond photoinduced electron transfer from conjugated polymers to functionalized fullerenes

Abstract: Subpicosecond photoinduced electron transfer from conjugated polymers to functionalized fullerenes Kraabel, B.; Hummelen, Jan C.; Vacar, D.; Moses, D.; Sariciftci, N. S.; Heeger, A. J.; Wudl, F.

Cited by 173 publications

References 18 publications

Nobel Lecture: Semiconducting and metallic polymers: The fourth generation of polymeric materials

Nobel Lecture: Semiconducting and metallic polymers: The fourth generation of polymeric materials

Charge generation in polymer–fullerene bulk-heterojunction solar cells

Reappraising the Need for Bulk Heterojunctions in Polymer−Fullerene Photovoltaics: The Role of Carrier Transport in All-Solution-Processed P3HT/PCBM Bilayer Solar Cells

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