Low-Energy Inverse Photoemission Study on the Electron Affinities of Fullerene Derivatives for Organic Photovoltaic Cells

Yoshida, Hiroyuki

doi:10.1021/jp509141y

Cited by 92 publications

(101 citation statements)

References 62 publications

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“…1c)34, and the IP and EA (electron affinity) of PC 71 BM were obtained from literatures35. The IP D of the three pristine films were 4.91, 4.98 and 5.05 eV, respectively, indicating fluorination of the end acceptors increase IP D comparing with those of fluorine atoms attached to the internal part of polymers3637.…”

Section: Resultsmentioning

confidence: 99%

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

et al. 2016

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Solution-processable small molecules for organic solar cells have attracted intense attention for their advantages of definite molecular structures compared with their polymer counterparts. However, the device efficiencies based on small molecules are still lower than those of polymers, especially for inverted devices, the highest efficiency of which is <9%. Here we report three novel solution-processable small molecules, which contain π-bridges with gradient-decreased electron density and end acceptors substituted with various fluorine atoms (0F, 1F and 2F, respectively). Fluorination leads to an optimal active layer morphology, including an enhanced domain purity, the formation of hierarchical domain size and a directional vertical phase gradation. The optimal morphology balances charge separation and transfer, and facilitates charge collection. As a consequence, fluorinated molecules exhibit excellent inverted device performance, and an average power conversion efficiency of 11.08% is achieved for a two-fluorine atom substituted molecule.

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Section: Resultsmentioning

confidence: 99%

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

et al. 2016

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“…Despite large differences in chemical and structural properties, both PC 71 BM and P(NDI2OD-T2) have similar E LUMO = ∼−3.8 eV (SI Appendix, Fig. S2) (56), and although absolute performance metrics differ, note that the metrics of all three OPV types consistently track each other, reaching performance maxima at 60 atom % Ga (CBM = −3.93 eV). Although it is likely that factors such as IFL conductivity and mobility play some role in the OPV metric trends observed here, the results in Fig.…”

Section: Significancementioning

confidence: 99%

“…The energy level alignment at different organic/oxide interface structures was next probed using combined UPS and LEIPS techniques. UPS measurements were performed on a-IGO films with 30, 60, and 80 atom % Ga (IGO-30, IGO-60, and IGO-80), stepwise coated with the organic acceptors having different LUMO energies derived from LEIPS as described above [ICBA (∼−3.5 eV), PC 71 BM (∼−3.8 eV) (56), and PDI-CN2 (∼−4.1 eV) (SI Appendix, Fig. S2)].…”

Section: Significancementioning

confidence: 99%

Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells

Zhou

Kim

Loser

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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In diverse classes of organic optoelectronic devices, controlling charge injection, extraction, and blocking across organic semiconductor-inorganic electrode interfaces is crucial for enhancing quantum efficiency and output voltage. To this end, the strategy of inserting engineered interfacial layers (IFLs) between electrical contacts and organic semiconductors has significantly advanced organic light-emitting diode and organic thin film transistor performance. For organic photovoltaic (OPV) devices, an electronically flexible IFL design strategy to incrementally tune energy level matching between the inorganic electrode system and the organic photoactive components without varying the surface chemistry would permit OPV cells to adapt to ever-changing generations of photoactive materials. Here we report the implementation of chemically/environmentally robust, low-temperature solution-processed amorphous transparent semiconducting oxide alloys, In-Ga-O and Ga-Zn-Sn-O, as IFLs for inverted OPVs. Continuous variation of the IFL compositions tunes the conduction band minima over a broad range, affording optimized OPV power conversion efficiencies for multiple classes of organic active layer materials and establishing clear correlations between IFL/photoactive layer energetics and device performance.interface | amorphous oxide | photovoltaic | interfacial layers S olar to electrical energy conversion technologies have received great attention as abundant and sustainable resources (1-5). The diffuse nature of solar energy requires low-cost, largearea devices while maintaining high power conversion efficiency (PCE) (3). As a universal design strategy, many of the emerging thin film photovoltaic (PV) technologies such as bulk heterojunction (BHJ) organic, perovskite, quantum dot (QD), and CIGS (Cu-InGa-Se) solar cells are fabricated using a trilayer architecture, where light absorbers are sandwiched between two electrodes coated with various interfacial layers (IFLs) (6-9). Stringent requirements govern ideal IFL materials design. Energetically, their respective band positions should match those of the photoinduced built-in potentials to provide energetically continuous carrier transport pathways and to accommodate the maximum allowed output voltage. In recent reports, PV performance enhancement via IFL energetic tuning has been demonstrated for very specific BHJ organic, QD, and perovskite cell compositions (6,8,10,11). However, true IFL energetic tunability has not been achieved and offers a challenging opportunity to optimize device performance.Fabricable from energetically diverse organic active layers, organic photovoltaics (OPVs) provide an excellent test bed for tuning IFL energetics and are the subject of this study. The basic BHJ OPV architecture contains a mesoscopically heterogeneous and isotropic, phase-separated donor-acceptor blend-a strategy to overcome the relatively short exciton diffusion lengths (∼10 nm) (2, 12, 13), sandwiched between hole-transporting (HT) and electron-transporting (ET) IFLs (2). Th...

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“…We have demonstrated that the electron affinity of organic materials can be determined with the precision comparable to the ionization energy determined by UPS. [27][28][29][30][31][32] Using this technique, we determined the electron affinity of BCP to be 1.9 eV. 30 This value is more than 1 eV smaller than the previously assumed one suggesting that the electron transport through the LUMO level of BCP is unlikely.…”

Section: Introductionmentioning

confidence: 99%

Electron Transport in Bathocuproine Interlayer in Organic Semiconductor Devices

Yoshida

2015

J. Phys. Chem. C

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When a thin layer of bathocuproine (BCP) is inserted between the metal electrode and organic layer of organic semiconductor device, the electron injection/collection efficiency at the interface is significantly improved. However, the mechanism of electron transport through the BCP layer has not been clarified yet. In this study, we directly observed the unoccupied electronic states of the Ag/BCP interface using low-energy inverse photoemission spectroscopy. The result shows that Ag strongly interacts with the BCP molecule and the lowest unoccupied molecular orbital (LUMO) level of the Ag-BCP complex aligns with the Fermi level indicating that the electron transport occurs through the LUMO level of the complex. With the aid of DFT calculation, we identify the reaction product

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Low-Energy Inverse Photoemission Study on the Electron Affinities of Fullerene Derivatives for Organic Photovoltaic Cells

Cited by 92 publications

References 62 publications

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells

Electron Transport in Bathocuproine Interlayer in Organic Semiconductor Devices

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