Low‐Bandgap Alternating Fluorene Copolymer/Methanofullerene Heterojunctions in Efficient Near‐Infrared Polymer Solar Cells

Zhang, Fengling; Mammo, Wendimagegn; Andersson, Lars M; Admassie, Shimelis; Andersson, Mats R.; Inganäs, Olle

doi:10.1002/adma.200600124

Cited by 330 publications

(185 citation statements)

References 28 publications

(54 reference statements)

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“…[65][66][67][68][69][70] Most of the structures are from the material classes of thiophene, fluorene, carbazole, and cyclopentadithiophene based copolymers. In addition, one typical low-band-gap polymer and a metallated conjugated polymer are discussed.…”

Section: Promising Donor Materialsmentioning

confidence: 99%

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Polymer‐Fullerene Bulk‐Heterojunction Solar Cells

Dennler¹,

Scharber²,

Brabec³

2009

Advanced Materials

3,089

2,455

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Solution‐processed bulk‐heterojunction solar cells have gained serious attention during the last few years and are becoming established as one of the future photovoltaic technologies for low‐cost power production. This article reviews the highlights of the last few years, and summarizes today's state‐of‐the‐art performance. An outlook is given on relevant future materials and technologies that have the potential to guide this young photovoltaic technology towards the magic 10% regime. A cost model supplements the technical discussions, with practical aspects any photovoltaic technology needs to fulfil, and answers to the question as to whether low module costs can compensate lower lifetimes and performances.

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Section: Promising Donor Materialsmentioning

confidence: 99%

“…[65,66,[71][72][73] Andersson et al prepared more than 10 different polyfluorene (PF) derivatives called APFO polymers. This class of polymers offers a sufficiently large variability in the position of the HOMO/LUMO levels, and polymers with a low band gap that show a photosensitivity down to 1 mm (polymer 2, Fig.…”

Section: Fluorene-based Copolymersmentioning

confidence: 99%

Polymer‐Fullerene Bulk‐Heterojunction Solar Cells

Dennler¹,

Scharber²,

Brabec³

2009

Advanced Materials

3,089

2,455

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“…[6][7][8] The majority of the improvement, however, came from the development of low band gap polymers. 3,4,[9][10][11][12][13][14][15][16][17] By decreasing the bandgap of the donor, the amount of absorbed photon flux increases due to an enhanced overlap with the solar spectrum. A lowering of the polymer band gap can either be achieved by a lowering of the lowest unoccupied molecular orbital (LUMO) or by a raise of the highest occupied molecular orbital (HOMO).…”

mentioning

confidence: 99%

Role of balanced charge carrier transport in low band gap polymer:Fullerene bulk heterojunction solar cells

Kotlarski

Moet

Blom

2011

J Polym Sci B Polym Phys

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Lowering of the optical band gap of conjugated polymers in bulk heterojunction solar cells not only leads to an increased absorption but also to an increase of the optimal active layer thickness due to interference effects at longer wavelengths. The increased carrier densities due to the enhanced absorption and thicker active layers make low band gap solar cells more sensitive to formation of space charges and recombination. By systematically red shifting the optical parameters of poly[2-methoxy-5-(3 0 ,7and 6,6-phenyl C 61 -butyric acid methyl ester, we simulate the effect of a reduced band gap on the solar cell efficiencies. We show that especially the fill factor of low band gap cells is very sensitive to the balance of the charge transport. For a low band gap cell with an active layer thickness of 250 nm, the fill factor of 50% for balanced transport is reduced to less than 40% by an imbalance of only one order of magnitude. The efficiency of organic polymer:fullerene bulk heterojunction solar cell performance has been steadily increasing in the last years, going from 2.5% efficiency in 2001 1 to 3.5% in 2003, 2 up to 5.5% in 2007, 3,4 and recently an efficiency of 7.4% has been reported. 5 Part of the improvement originated from the refinement of existing production techniques to optimize the active layer morphology.6-8 The majority of the improvement, however, came from the development of low band gap polymers. 3,4,[9][10][11][12][13][14][15][16][17] By decreasing the bandgap of the donor, the amount of absorbed photon flux increases due to an enhanced overlap with the solar spectrum. A lowering of the polymer band gap can either be achieved by a lowering of the lowest unoccupied molecular orbital (LUMO) or by a raise of the highest occupied molecular orbital (HOMO). The lowering of the LUMO is limited by the energy offset needed for electron transfer to the acceptor, typically 0.4 eV. A raise of the HOMO on the other hand will lead to a decrease of the open circuit voltage V oc . A theoretical study by Koster et al. 18 showed that a decrease of the bandgap from 2.1 to 1.5 eV, by lowering the LUMO and keeping the HOMO in place, is expected to result in an increase in power conversion efficiency g from 3.5% to over 8%. This enhanced performance mainly originated from an increased short circuit current density J sc due to an increased absorption. However, an increased absorption because of a better spectral overlap with the solar sprectrum also leads to an increased concentration of electrons and holes in the solar cells. This enhancement of the carrier density then gives rise to an increase of the bimolecular recombination, which is proportional to the product of the electron and hole density. Furthermore, the higher carrier densities make the solar cells also more sensitive for the built-up of space charge, caused by an imbalanced charge transport. Space charge built-up is also dependent on the absorption profiles in the solar cell, which were not included in these calculations. To obtain more in...

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“…The bulk heterojunction structure composed of interpenetrating network of polymer donor and electron acceptor has greatly promoted the development of polymer solar cells [8]. In the past two decades, a large variety of polymer donor materials have been tested [9][10][11][12][13][14][15]. In contrast to polymer donors, the diversity of electron acceptors remains rather small.…”

Section: Introductionmentioning

confidence: 99%