The Role of Transition Metal Oxides in Charge‐Generation Layers for Stacked Organic Light‐Emitting Diodes

Hamwi, Sami; Meyer, Jens; Kröger, Michael; Winkler, Thomas; Witte, M.; Riedl, Thomas; Kahn, Antoine; Kowalsky, Wolfgang

doi:10.1002/adfm.201000301

Cited by 153 publications

(136 citation statements)

References 25 publications

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“…[ 14 ] However, recent publications by Kahn et al suggest a very deep lying conducting band at -6.7 eV for MoO 3 and a high work function of -6.9 eV. [15][16][17] According to this model MoO 3 acts as a n-type semiconductor.…”

Section: Resultsmentioning

confidence: 95%

Simple, Highly Efficient Vacuum‐Processed Bulk Heterojunction Solar Cells Based on Merocyanine Dyes

Steinmann

Kronenberg

Lenze

et al. 2011

Advanced Energy Materials

141

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In order to be competitive on the energy market, organic solar cells with higher efficiency are needed. To date, polymer solar cells have retained the lead with efficiencies of up to 8%. However, research on small molecule solar cells has been catching up throughout recent years and is showing similar efficiencies, however, only for more sophisticated multilayer device configurations. In this work, a simple, highly efficient, vacuum‐processed small molecule solar cell based on merocyanine dyes – traditional colorants that can easily be mass‐produced and purified – is presented. In the past, merocyanines have been successfully introduced in solution‐processed as well as vacuum‐processed devices, demonstrating efficiencies up to 4.9%. Here, further optimization of devices is achieved while keeping the same simple layer stack, ultimately leading to efficiencies beyond the 6% mark. In addition, physical properties such as the charge carrier transport and the cell performance under various light intensities are addressed.

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Section: Resultsmentioning

confidence: 95%

Simple, Highly Efficient Vacuum‐Processed Bulk Heterojunction Solar Cells Based on Merocyanine Dyes

Steinmann

Kronenberg

Lenze

et al. 2011

Advanced Energy Materials

141

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“…[29][30][31] Figure 2 a shows the Mo 3d XPS core level of a MoO 3 fi lm deposited on an ITO substrate. The pristine MoO 3 fi lm exhibits a pair of orbital spin splitting peaks with Mo 3d 5/2 (232.7 eV) and Mo 3d 3/2 (235.8 eV), indicating the existence of Mo 6+ cations.…”

Section: Doi: 101002/admi201300082mentioning

confidence: 99%

Suppression of Time‐Dependent Donor/Acceptor Interface Degradation by Redistributing Donor Charge Density

et al. 2014

Adv Materials Inter

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organic interface, where reactive oxygen species generated by UV-ozone treatment of the indium-tin oxide (ITO) substrate slowly degrade the organic layer. [ 8 ] Other than the degradation related to the organic/electrode interface, we show here that a time-dependent chemical reaction at the donor/acceptor interface can also cause device deterioration. We further show that the donor/acceptor chemical reaction can be suppressed by introducing a strong electron-drawing MoO 3 layer aside to the SubPc fi lm. Stability enhancing capability of MoO 3 has been reported in both OPV device and organic light emitting devices (OLED). Yet, all previous reports suggest that the effects are mainly attributed to the spatial isolation of organic fi lm from electrode; and the reduction of the energetic transport barrier. [ 6,[25][26][27] Here, we show a new mechanism that chemical reactions between two organic fi lms can be modulated by the formation CTC. Due to the high electron affi nity, the incorporation of the MoO 3 layer results in strong charge interaction between MoO 3 and SubPc. The resulting CTC leads to subtle charge re-distribution in SubPc donor molecules that inhibits further chemical reaction at SubPc/C 60 interface. It is the fi rst demonstration that an interfacial chemical reaction at donor/acceptor junction can be controlled by charge modulation and carrier redistribution.The bottom spectrum (labeled as C 60 , 0 hr) in Figure 1 a shows an XPS C1s core level spectrum of a thin C 60 (2 nm) fi lm freshly deposited on an ITO/SubPc (5 nm) substrate. After storage of 4 h in an ultrahigh vacuum (UHV) of 10 −9 Torr, the C1s peak slightly shifts by 0.13 eV from 285.07 to 285.20 eV (labeled as C 60 , 4 hrs). Corresponding changes in the B1s core level from the SubPc layer are shown in the upper two spectra in Figure 1 b. Upon 4-hours aging, the B1s peak shifts by 0.15 eV from 191.7 to 191.85 eV. These spectral shifts indicate substantial charge re-distribution in both the C 60 and the SubPc fi lms upon aging in UHV.It is also noted that an additional new peak emerges at 187.2 eV in the B1s core level (C 60 , 4 hrs in Figure 1 b) after the 4-hours aging, indicating the B atom in the SubPc molecule has gained electrons by forming a new boride bond. [ 28 ] A similar aging experiment is repeated using an ITO/SubPc substrate without C 60 deposition. No additional peak is observed over the same aging time (i.e. dashed lines in Figure 1 b). It is thus reasonable to attribute the new boron peak to boride bond formed at the SubPc/C 60 contact upon aging.Poor operation stability is a major hurdle for the wide application of organic photovoltaic (OPV) devices. While most attention is given to environmental threats to device stability, we herein show evidence from X-ray photoemission spectroscopy (XPS) of an intrinsic time-dependent chemical reaction at a donor/ acceptor interface. Albeit with impressive device performance from boron subphthalocyanine chloride (SubPc)/ fullerene (C 60 ) interface, the forming boride bonds at its inter...

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“…The mechanism of charge recombination in our tandem cells is in inverse analogy to that evidenced previously in multijunction organic light emitting diodes (OLEDs), where the individual light emitting units are connected by so-called charge generation layers which comprised high-WF TMOs. [43] Moreover, the working principle in our interconnects contrasts the established picture used in the case of highly doped organic p-/n-type tunnel junctions, which have been frequently used in tandem cells. [39] There, charge recombination occurs in the center of the interconnect as electrons tunnel from the lowest unoccupied molecular orbital (LUMO) of the n-doped electron transport layer to the HOMO of the p-doped hole transport layer.…”

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confidence: 99%

All‐Oxide MoO_x/SnO_x Charge Recombination Interconnects for Inverted Organic Tandem Solar Cells

Becker

Trost

Behrendt

et al. 2017

Advanced Energy Materials

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Multijunction solar cells are designed to improve the overlap with the solar spectrum and to minimize losses due to thermalization. Aside from the optimum choice of photoactive materials for the respective sub‐cells, a proper interconnect is essential. This study demonstrates a novel all‐oxide interconnect based on the interface of the high‐work‐function (WF) metal oxide MoOx and low‐WF tin oxide (SnOx). In contrast to typical p‐/n‐type tunnel junctions, both the oxides are n‐type semiconductors with a WF of 5.2 and 4.2 eV, respectively. It is demonstrated that the electronic line‐up at the interface of MoOx and SnOx comprises a large intrinsic interface dipole (≈0.8 eV), which is key to afford ideal alignment of the conduction band of MoOx and SnOx, without the requirement of an additional metal or organic dipole layer. The presented MoOx/SnOx interconnect allows for the ideal (loss‐free) addition of the open circuit voltages of the two sub‐cells.

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The Role of Transition Metal Oxides in Charge‐Generation Layers for Stacked Organic Light‐Emitting Diodes

Cited by 153 publications

References 25 publications

Simple, Highly Efficient Vacuum‐Processed Bulk Heterojunction Solar Cells Based on Merocyanine Dyes

Simple, Highly Efficient Vacuum‐Processed Bulk Heterojunction Solar Cells Based on Merocyanine Dyes

Suppression of Time‐Dependent Donor/Acceptor Interface Degradation by Redistributing Donor Charge Density

All‐Oxide MoO_x/SnO_x Charge Recombination Interconnects for Inverted Organic Tandem Solar Cells

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The Role of Transition Metal Oxides in Charge‐Generation Layers for Stacked Organic Light‐Emitting Diodes

Cited by 153 publications

References 25 publications

Simple, Highly Efficient Vacuum‐Processed Bulk Heterojunction Solar Cells Based on Merocyanine Dyes

Simple, Highly Efficient Vacuum‐Processed Bulk Heterojunction Solar Cells Based on Merocyanine Dyes

Suppression of Time‐Dependent Donor/Acceptor Interface Degradation by Redistributing Donor Charge Density

All‐Oxide MoOx/SnOx Charge Recombination Interconnects for Inverted Organic Tandem Solar Cells

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Product

Resources

About

All‐Oxide MoO_x/SnO_x Charge Recombination Interconnects for Inverted Organic Tandem Solar Cells