C<sub>60</sub>:LiF Blocking Layer for Environmentally Stable Bulk Heterojunction Solar Cells

Gao, Dong; Helander, Michael G.; Wang, Zhibin; Puzzo, Daniel P.; Greiner, Mark; Lu, Zheng‐Hong

doi:10.1002/adma.201002738

Cited by 63 publications

(39 citation statements)

References 46 publications

(47 reference statements)

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“…Even though this efficiency (of 3.94%) is lower than the efficiency reported from devices made with P3HT: PCBM blends where the complete process was performed under controlled atmosphere [34], this efficiency (of 3.94%) compares well with reported PCE values from devices fabricated through air exposure and is even higher than the recently reported PCE value of 3.54% for devices made with an interlayer of a C 60 -LiF mixture [13]. As the P3HT:PCBM active layer is extremely sensitive to photo-oxidation this effect was reported to be the primary degradation mechanism in OPVs [13]. Even the minimum amount of moisture and oxygen that might have diffused through the top layer in the first few hours of operation still managed to rapidly degrade the device.…”

Section: -P7supporting

confidence: 57%

“…For further improvement of polymer solar cell performances, the research and development on the interfacial modification between the BHJ active layer and the cathode electrode is an ongoing topic of discussion in recent days [8][9][10][11][12][13]. Various types of materials have been used as interfacial layers in the field of organic solar cells and each type of layer could have a different role [8].…”

Section: Introductionmentioning

confidence: 99%

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Improved polymer solar cell performance by engineering of cathode interface

Baral

Izquierdo

Packirisamy

et al. 2011

Eur. Phys. J. Appl. Phys.

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Abstract. By engineering the interface between the intermediate photoactive layer and the cathode aluminum (Al) electrode, through the introduction of ultra-thin layers of various materials, in a standard bulk heterojunction (BHJ) polymer solar cell (PSC) fabricated of regioregular poly(3-hexylthiophene) (rr-P3HT) and phenyl-C 61-butyric acid methyl ester (PCBM), the power conversion efficiency (PCE) has been effectively improved. The devices fabricated using individual single interlayer of bathocuproine (BCP), lithium fluoride (LiF) and Buckminster fullerene C60 have shown optimal efficiencies of ∼2.40%, ∼3.21% and ∼1.92% respectively. Further improvement of the photovoltaic efficiency was achieved by introducing a composite bilayer made of LiF in combination with BCP as well as with C60 at the BHJ/cathode interface. The best results were obtained by interposing a 9 nm of C60 interlayer in combination with a 0.9 nm thick LiF layer, with the PCE of the PV cells being effectively increased up to 3.94% which represents an improvement of 23% as compared to the standard device with LiF interlayer alone. The photocurrent density (J sc) versus voltage (V ) characteristic curves shows that the increase of the efficiency is essentially due to an increase in Jsc. Moreover, all the sets of devices fabricated using various interlayers over a certain range of thickness exhibit an optimum PCE that is inversely proportional to the series resistance of the PV cells. We presume that interposing a C60/LiF layer at the interface could repair the poor contact at the electron acceptor/cathode interface and improve the charge career extraction from the BHJ.

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Section: -P7supporting

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Improved polymer solar cell performance by engineering of cathode interface

Baral

Izquierdo

Packirisamy

et al. 2011

Eur. Phys. J. Appl. Phys.

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“…6,7 Due to the rich electronic properties in the ground and excited states, C 60 is most widely used as an organic semiconductor. With the ability to act as both an electron acceptor and donor, it is a standard material in organic light emitting diodes, solar cells, transistors and Schottky diodes.The interface with the metal contacts play a crucial role in the effectiveness of organic semiconductors in device performance and stability.8 Introducing a thin buffer layer of LiF between an organic film and an Al cathode has been seen to dramatically enhance the energy-level alignment and stability of the interface.9-13 Additionally, alternating stacks of LiF and C 60 14 and LiF doped C 60 nanocomposite buffer layers 15,16 have been shown to have high conductivities and stability in OLEDs and OPVs. Several mechanisms have been proposed for these behaviors including chemical reactions, dipole alignment, tunneling, and LiF dissociation requiring the additional presence of Al.…”

mentioning

confidence: 99%

“…8 Introducing a thin buffer layer of LiF between an organic film and an Al cathode has been seen to dramatically enhance the energy-level alignment and stability of the interface. [9][10][11][12][13] Additionally, alternating stacks of LiF and C 60 14 and LiF doped C 60 nanocomposite buffer layers 15,16 have been shown to have high conductivities and stability in OLEDs and OPVs. Several mechanisms have been proposed for these behaviors including chemical reactions, dipole alignment, tunneling, and LiF dissociation requiring the additional presence of Al.…”

mentioning

confidence: 99%

“…9-13 Additionally, alternating stacks of LiF and C 60 14 and LiF doped C 60 nanocomposite buffer layers 15,16 have been shown to have high conductivities and stability in OLEDs and OPVs. Several mechanisms have been proposed for these behaviors including chemical reactions, dipole alignment, tunneling, and LiF dissociation requiring the additional presence of Al.…”

mentioning

confidence: 99%

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LiF Doping of C₆₀Studied with X-ray Photoemission Shake-Up Analysis

Turak

Zgierski

Dharma‐wardana

2017

ECS J. Solid State Sci. Technol.

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We report our investigation of the chemical doping mechanism induced by LiF interaction with fullerene thin films. High resolution Xray photoelectron spectroscopy of the C1s shake-up satellites and F1s main core level, supported by density functional calculations, suggest the formation of a charge transfer complex between covalent LiF monomers and dimers and C 60 . This interaction was observed in both LiF/C 60 and C 60 /LiF depositions, suggesting that some charge transfer complexation can occur in these systems even without dissociation. hydrogen storage materials, 5 and even antibacterial treatments. 6,7 Due to the rich electronic properties in the ground and excited states, C 60 is most widely used as an organic semiconductor. With the ability to act as both an electron acceptor and donor, it is a standard material in organic light emitting diodes, solar cells, transistors and Schottky diodes.The interface with the metal contacts play a crucial role in the effectiveness of organic semiconductors in device performance and stability.8 Introducing a thin buffer layer of LiF between an organic film and an Al cathode has been seen to dramatically enhance the energy-level alignment and stability of the interface.9-13 Additionally, alternating stacks of LiF and C 60 14 and LiF doped C 60 nanocomposite buffer layers 15,16 have been shown to have high conductivities and stability in OLEDs and OPVs. Several mechanisms have been proposed for these behaviors including chemical reactions, dipole alignment, tunneling, and LiF dissociation requiring the additional presence of Al. 17In this contribution, we present results showing that in the absence of Al, there is a charge transfer interaction between LiF and C 60 , leading to the formation of LiF••C 60 complexes without dissociation. Using the well-developed and described X-ray photoelectron shakeup structure of C 60 and the strong feature from F1s XPS core level, we see evidence of a direction independent interaction. The spectroscopic features can be described by the semi-covalent interaction of LiF monomers or dimers with C 60 using density functional theory. Coupled with XPS core level shift calculations, using approximate Madelung energy, the predicted Millikan charges and bond lengths give values that approximate the observed core level shifts. Additionally, the small transfer of charge to C 60 predicted by the modelling is consistent with the minimal impact on the shake-up satellites of the C1s of C 60 . ExperimentalThe samples were produced using a Kurt J. Lesker OLED cluster attached to an X-ray photoelectron spectroscopy tool. For deposition of C 60 , ∼5Å of LiF on 100 nm sputter deposited Au/Si was used z E-mail: turaka@mcmaster.ca as a substrate. For deposition of LiF, the substrate was 350Å of C 60 thermally deposited onto cleaned Si with native oxide. C 60 and LiF were thermally evaporated from home built crucible sources at an average rate of 1 Å/min and 2-3 Å/hr as measured by oscillating quartz crystal microbalance (Inficon XTM/2) respectively onto previ...

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