Correlation of Absorption Profile and Fill Factor in Organic Solar Cells: The Role of Mobility Imbalance

Tress, Wolfgang; Merten, A.; Furno, Mauro; Hein, Moritz; Leo, Karl; Riede, Moritz

doi:10.1002/aenm.201200835

Cited by 52 publications

(68 citation statements)

References 27 publications

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“…1. 15,22,23 (a) An injection barrier is formed when the work function of the MeO x is below the Fermi level, the LUMO level of PCBM, respectively. Such an injection barrier prevents electron injection at the MeO x /PCBM interface.…”

Section: -4mentioning

confidence: 99%

A solution-processed barium hydroxide modified aluminum doped zinc oxide layer for highly efficient inverted organic solar cells

Zhang

Stubhan

et al. 2014

J. Mater. Chem. A

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Inverted organic solar cells (iOSCs) with air stable interface materials and top electrodes and an efficiency of 6.01% are achieved by inserting a barium hydroxide (Ba(OH) 2 ) layer between the aluminum doped zinc oxide (AZO) electron extraction layer and the active layer. A low bandgap diketopyrrolopyrrolequinquethiophene alternating copolymer (pDPP5T-2) and phenyl-C61-butyric acid methyl ester (PC 61 BM) were chosen as the active layer compounds. Compared to the control device without Ba(OH) 2 , insertion of a few nm thick Ba(OH) 2 layer results in an enhanced V OC of 10%, J SC of 28%, FF of 28% and PCE of 80%. Modification of AZO with a solution processed low-cost Ba(OH) 2 layer increased the efficiency of the inverted device by dominantly reducing the energy barrier for electron extraction from PC 61 BM, and consequently, reduced charge recombination is observed. The drastic improvement in device efficiency and the simplicity of fabrication by solution processing suggest Ba(OH) 2 as a promising and practical route to reduce interface induced recombination losses at the cathode of organic solar cells.

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Section: -4mentioning

confidence: 99%

A solution-processed barium hydroxide modified aluminum doped zinc oxide layer for highly efficient inverted organic solar cells

Zhang

Stubhan

et al. 2014

J. Mater. Chem. A

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“…Whilst charge mobilities are low in organic semiconductors and collection losses have been shown to limit the fill factor (FF) [3][4][5] and short circuit current density (J SC ) [6][7][8][9][10] of certain devices, low mobilities do not necessarily prevent devices from performing efficiently. However the lower charge mobilities and diffusion coefficients in organic semiconductors do mean that diffusion alone is insufficient for charge carrier collection and drift must account for a large proportion of the generated photocurrent.…”

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confidence: 99%

Influence of doping on charge carrier collection in normal and inverted geometry polymer:fullerene solar cells

Dibb

Muth

Kirchartz

et al. 2013

Sci Rep

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While organic semiconductors used in polymer:fullerene photovoltaics are generally not intentionally doped, significant levels of unintentional doping have previously been reported in the literature. Here, we explain the differences in photocurrent collection between standard (transparent anode) and inverted (transparent cathode) low band-gap polymer:fullerene solar cells in terms of unintentional p-type doping. Using capacitance/voltage measurements, we find that the devices exhibit doping levels of order 10 16 cm 23 , resulting in space-charge regions ,100 nm thick at short circuit. As a result, low field regions form in devices thicker than 100 nm. Because more of the light is absorbed in the low field region in standard than in inverted architectures, the losses due to inefficient charge collection are greater in standard architectures. Using optical modelling, we show that the observed trends in photocurrent with device architecture and thickness can be explained if only charge carriers photogenerated in the depletion region contribute to the photocurrent.T he record power conversion efficiency (PCE) achieved by polymer:fullerene solar cells has increased considerably in the past 4 years to a record published value of 9.2% 1 for a single bulk heterojunction and efficiencies of 10.6% for tandem solar cells 2 . This is despite the fact that organic semiconductors are known to be both structurally and electronically disordered, have lower dielectric constants inhibiting separation of the photogenerated excitonic species and have charge carrier mobilities orders of magnitude lower than inorganic semiconductors.Whilst charge mobilities are low in organic semiconductors and collection losses have been shown to limit the fill factor (FF) 3-5 and short circuit current density (J SC ) 6-10 of certain devices, low mobilities do not necessarily prevent devices from performing efficiently. However the lower charge mobilities and diffusion coefficients in organic semiconductors do mean that diffusion alone is insufficient for charge carrier collection and drift must account for a large proportion of the generated photocurrent. Additionally, polymer:fullerene solar cells are not intentionally doped like their inorganic counterparts or like many small molecule solar cells 11 and therefore rely on selective contacts and the difference in work function between electrodes for efficient charge collection. However, several studies have found evidence for unintentional doping [12][13][14][15][16][17][18][19] and discussed the consequences for device behaviour 6,[20][21][22][23][24][25][26][27][28][29][30] . Whilst the origin of this doping is unclear 15 , its effects on photovoltaic performance can be substantial; however many recent analyses of device performance neglect doping 8,[31][32][33] despite the fact that the influence of doping and the electric field on charge carrier collection is well known for a long time 34 and wellstudied for instance in the field of quantum dot photovoltaics 35,36 .In this paper, we address the...

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“…This open-circuit voltage is far the highest reported value. Usually, V OC is between 0.5 and 0.6 as reported by Tress et al [18,19]. We address this higher value to a higher degree of purity provided by the BASF company.…”

Section: Resultsmentioning

confidence: 86%

Highly sensitive wide range organic photodiode based on zinc phthalocyanine:C₆₀

Döring

Otto

Cehovski

et al. 2016

Physica Status Solidi (a)

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We report on the preparation and characterization of a highly sensitive organic photodiode for the entire visible part of the spectrum. The photodiode is based on a small molecule heterojunction layer of zinc phthalocyanine (ZnPC) and fullerene C 60 and is prepared by multistep vacuum deposition technique. Investigation is performed under different illumination conditions, from spectrally broad to narrow line, cw and pulsed, to determine linearity of operation, responsivity, quantum efficiency, dark current, and detectivity. The experimental results in combination with a simple device stack favor ZnPC:C 60 as active layer in organic photodiodes, e.g., for opto-electronic sensor systems.

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Correlation of Absorption Profile and Fill Factor in Organic Solar Cells: The Role of Mobility Imbalance

Cited by 52 publications

References 27 publications

A solution-processed barium hydroxide modified aluminum doped zinc oxide layer for highly efficient inverted organic solar cells

A solution-processed barium hydroxide modified aluminum doped zinc oxide layer for highly efficient inverted organic solar cells

Influence of doping on charge carrier collection in normal and inverted geometry polymer:fullerene solar cells

Highly sensitive wide range organic photodiode based on zinc phthalocyanine:C₆₀

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Correlation of Absorption Profile and Fill Factor in Organic Solar Cells: The Role of Mobility Imbalance

Cited by 52 publications

References 27 publications

A solution-processed barium hydroxide modified aluminum doped zinc oxide layer for highly efficient inverted organic solar cells

A solution-processed barium hydroxide modified aluminum doped zinc oxide layer for highly efficient inverted organic solar cells

Influence of doping on charge carrier collection in normal and inverted geometry polymer:fullerene solar cells

Highly sensitive wide range organic photodiode based on zinc phthalocyanine:C60

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Product

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Highly sensitive wide range organic photodiode based on zinc phthalocyanine:C₆₀