Enhanced spectral coverage in tandem organic solar cells

Dennler, Gilles; Prall, Hans-Jürgen; Koeppe, Robert A.; Egginger, Martin; Autengruber, Robert; Sariciftci, Niyazi Serdar

doi:10.1063/1.2336593

Cited by 166 publications

(119 citation statements)

References 23 publications

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“…Although layers of PCBM have been spin-cast from DCM onto P3HT films in the past, 34,35 there has been essentially no work investigating either the quality of the PCBM films produced by spin-coating or the effects of spinning the PCBM top layer onto the P3HT underlayer. Thus, we begin this section with a detailed examination of the morphology of our spin-cast P3HT/PCBM bilayers.…”

Section: Resultsmentioning

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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Section: Resultsmentioning

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 first reported devices consisted of a stack of two (poly[2-(3,7-dimethyloctyloxy)-5-methyloxy]-paraphenylene vinylene) (MDMO-PPV):1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C 61 (PC 60 BM) devices, [104] interconnected by a directcurrent magnetron sputtered ITO layer. The first tandem cell comprising two different absorbers was realized by hybrid www.advmat.de technology, [105] based on a bottom cell processed from solution (P3HT:PCBM) and a top cell evaporated (ZnP C :C 60 ), both subdevices being separated by 1 nm of Au. Further reports followed up this hybrid solution, with other material combinations.…”

Section: Tandem Cellsmentioning

confidence: 99%

Polymer‐Fullerene Bulk‐Heterojunction Solar Cells

Dennler¹,

Scharber²,

Brabec³

2009

Advanced Materials

Self Cite

3,123

2,461

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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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“…However, the narrow absorption properties combined with low charge carrier mobilities limit the performance of the organic solar cells [1,2]. One way to improve the absorption of organic solar cells is by using tandem (or multi-junction) structures [3][4][5][6][7][8][9][10]. Because of the different band gap of the active layer each sub cell then absorbs light in a different part of the solar spectrum.…”

Section: Introductionmentioning

confidence: 99%

“…In Fig. 1 the current-voltage characteristics are shown for a tandem cell based on a 250 nm blend of regioregular poly(3-hexylthiophene) (rr-P3HT) and the fullerene derivative [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) for the bottom cell and a 80 nm blend of poly(2-methoxy-5-(3 0 ,7 0 -dimethyloctyloxy)-p-phenylene vinylene) (MDMO-PPV) and PCBM for the top cell. An optical spacer with a thickness of 190 nm was used to separate the sub cells.…”

Section: Introductionmentioning

confidence: 99%

Device operation of organic tandem solar cells

Hadipour

Boer

Blom

2008

Organic Electronics

120

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Enhanced spectral coverage in tandem organic solar cells

Cited by 166 publications

References 23 publications

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

Polymer‐Fullerene Bulk‐Heterojunction Solar Cells

Device operation of organic tandem solar cells

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