Valence band edge tail states and band gap defect levels of GaN bulk and InxGa1−xN films detected by hard X-ray photoemission and photothermal deflection spectroscopy

Sumiya, Masatomo; Ueda, Shigenori; Fukuda, Kiyotaka; Asai, Yuya; Cho, Yujin; Sang, Liwen; Uedono, Akira; Sekiguchi, Takashi; Onuma, Takeyoshi; Honda, Toshio

doi:10.7567/apex.11.021002

Cited by 19 publications

(8 citation statements)

References 31 publications

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“…To further understand the influence of CsBr on sp-NiO x film, we measured the defect levels in the band gap of NiO x by using photothermal deflection spectroscopy (PDS). − The band gap of sp-NiO x was estimated to be 3.6–3.7 eV from UV–visible absorption spectra. The slopes between 3.30 and 3.80 eV for pristine sp-NiO x and CsBr modified sp-NiO x were 0.74 and 0.86, respectively, as shown in Figure .…”

Section: Results and Discussionmentioning

confidence: 99%

Passivation of Bulk and Interface Defects in Sputtered-NiO_x-Based Planar Perovskite Solar Cells: A Facile Interfacial Engineering Strategy with Alkali Metal Halide Salts

Pant

Kulkarni

Yanagida

et al. 2021

ACS Appl. Energy Mater.

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Nickel oxide (NiO x ) (deposited by sputtering (sp)) is a promising hole transport layer (HTL) for inverted planar perovskite solar cells. However, poor CH 3 NH 3 PbI 3 crystallization, elimination of CH 3 NH 3 + , and formation of residual PbI 2 grains, induced by defects present on the surface of sp-NiO x , have limited the device efficiency. Herein, a facile approach is reported to passivate the surface defects in sp-NiO x and simultaneously induce complete perovskite crystallization (without residual PbI 2 grains) via modifying the sp-NiO x /CH 3 NH 3 PbI 3 interface with various alkali metal halide salts (AMHSs). Comprehensive film and device characterizations reveal the additional influence of AMHSs, especially cesium bromide (CsBr), on the structural, morphological, photophysical, and photovoltaic performance. It is found that incorporation of a CsBr interlayer significantly improves the perovskite crystallization, producing high-quality MAPbI 3 films with enlarged grain sizes (without any residual PbI 2 grains) contrasting without the CsBr-interlayer case. CsBr (and other AMHSs) additionally reduces the band tail states and passivates the surface defects in sp-NiO x (as revealed by X-ray photoelectron spectroscopy and photodeflection spectroscopy), thereby suppressing interfacial disorder and recombination centers and improving the overall charge collection property across the sp-NiO x /CH 3 NH 3 PbI 3 interface. This leads to improvement in the device efficiency (with active area = 1 cm 2 ) and long-term operational stability at the maximum power point under continuous illumination for 8000 s and against ambient atmosphere for ∼2200 h. On the basis of the results, a possible crystallization process is discussed which provides insights into the engineering of the sp-NiO x /CH 3 NH 3 PbI 3 interface rendering improved device performance.

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Section: Results and Discussionmentioning

confidence: 99%

Passivation of Bulk and Interface Defects in Sputtered-NiO_x-Based Planar Perovskite Solar Cells: A Facile Interfacial Engineering Strategy with Alkali Metal Halide Salts

Pant

Kulkarni

Yanagida

et al. 2021

ACS Appl. Energy Mater.

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“…Photothermal deflection spectroscopy (PDS) was used for different treatments of the NiO x surface to characterize the defect levels present in the perovskite/NiO x and NiO x /ITO bandgaps. PDS is a suitable method because it enables the detection of the defect levels for all charge states within the measured sample depth; it detects the charge states in accordance with the absorption coefficient. − In this case, monochromatic light was used to irradiate the sample surface. The light source was a halogen lamp modulated at a chopping frequency ranging between 7 and 11 Hz with incident light at a normal angle to the sample surface.…”

Section: Methodsmentioning

confidence: 99%

Surface Passivation of Sputtered NiO_x Using a SAM Interface Layer to Enhance the Performance of Perovskite Solar Cells

et al. 2022

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Sputtered NiO x (sp-NiO x ) is a preferred hole transporting material for perovskite solar cells because of its hole mobility, ease of manufacturability, good stability, and suitable Fermi level for hole extraction. However, uncontrolled defects in sp-NiO x can limit the efficiency of solar cells fabricated with this hole transporting layer. An interfacial layer has been proposed to modify the sp-NiO x /perovskite interface, which can contribute to improving the crystallinity of the perovskite film. Herein, a 2-(3,6-dimethoxy-9 H -carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) self-assembled monolayer was used to modify an sp-NiO x surface. We found that the MeO-2PACz interlayer improves the quality of the perovskite film due to an enlarged domain size, reduced charge recombination at the sp-NiO x /perovskite interface, and passivation of the defects in sp-NiO x surfaces. In addition, the band tail states are also reduced, as indicated by photothermal deflection spectroscopy, which thus indicates a reduction in defect levels. The overall outcome is an improvement in the device efficiency from 11.9% to 17.2% due to the modified sp-NiO x /perovskite interface, with an active area of 1 cm 2 (certified efficiency of 16.25%). On the basis of these results, the interfacial engineering of the electronic properties of sp-NiO x /MeO-2PACz/perovskite is discussed in relation to the improved device performance.

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“…To further investigate the polymer order in depth, we conducted photothermal deflection spectroscopy (PDS) of the NPI-based polymers and PNPE2T (Figure a). − The PDS signals of the polymers dropped at the energy corresponding to the band gap, which was consistent with their UV–vis–NIR absorption spectra. We estimated the Urbach energy ( E U ) from the following equation using a fit to the PDS spectra: α( E ) = α 0 exp[( E g – E 0 )/ E U ], where α 0 and E 0 are constants .…”

Section: Resultsmentioning

confidence: 60%

Naphthobispyrazine Bisimide: A Strong Acceptor Unit for Conjugated Polymers Enabling Highly Coplanar Backbone, Short π–π Stacking, and High Electron Transport

et al. 2022

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The development of acceptor units that ensure high electron transport in π-conjugated polymers is imperative to advance the field of printable electronics. We have designed and synthesized naphthobispyrazine bisimide (NPI) as a novel strong acceptor unit by chemical conversion from naphthobispyrazine tetraester (NPE). We have also synthesized NPI-based polymers using bithiophene derivatives with and without fluorine groups as co-monomers. Notably, the NPI polymer-based transistors demonstrated ambipolar characteristics with hole and electron mobilities of up to 0.8 and 0.7 cm2 V–1 s–1, respectively, despite the unfavorable face-on orientation, and those values were more than 2 orders of magnitude higher than the hole and electron mobilities of their NPE counterpart. We ascribed the greatly enhanced mobilities to the highly coplanar and rigid backbone and the quite high crystallinity along with the short π–π stacking distances of the order of 3.4 Å, which resulted in efficient intra- and interchain charge carrier transport. We also found that the fluorine atom can act as a conformation-directing group, depending on the substitution position, which led to a more regular backbone structure with reduced energetic disorder while achieving higher solubility. We showed that NPI is a promising acceptor unit for high-performance electron-transporting π-conjugated polymers.

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Valence band edge tail states and band gap defect levels of GaN bulk and In_xGa₁₋_xN films detected by hard X-ray photoemission and photothermal deflection spectroscopy

Cited by 19 publications

References 31 publications

Passivation of Bulk and Interface Defects in Sputtered-NiO_x-Based Planar Perovskite Solar Cells: A Facile Interfacial Engineering Strategy with Alkali Metal Halide Salts

Passivation of Bulk and Interface Defects in Sputtered-NiO_x-Based Planar Perovskite Solar Cells: A Facile Interfacial Engineering Strategy with Alkali Metal Halide Salts

Surface Passivation of Sputtered NiO_x Using a SAM Interface Layer to Enhance the Performance of Perovskite Solar Cells

Naphthobispyrazine Bisimide: A Strong Acceptor Unit for Conjugated Polymers Enabling Highly Coplanar Backbone, Short π–π Stacking, and High Electron Transport

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Valence band edge tail states and band gap defect levels of GaN bulk and InxGa1−xN films detected by hard X-ray photoemission and photothermal deflection spectroscopy

Cited by 19 publications

References 31 publications

Passivation of Bulk and Interface Defects in Sputtered-NiOx-Based Planar Perovskite Solar Cells: A Facile Interfacial Engineering Strategy with Alkali Metal Halide Salts

Passivation of Bulk and Interface Defects in Sputtered-NiOx-Based Planar Perovskite Solar Cells: A Facile Interfacial Engineering Strategy with Alkali Metal Halide Salts

Surface Passivation of Sputtered NiOx Using a SAM Interface Layer to Enhance the Performance of Perovskite Solar Cells

Naphthobispyrazine Bisimide: A Strong Acceptor Unit for Conjugated Polymers Enabling Highly Coplanar Backbone, Short π–π Stacking, and High Electron Transport

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Valence band edge tail states and band gap defect levels of GaN bulk and In_xGa₁₋_xN films detected by hard X-ray photoemission and photothermal deflection spectroscopy

Passivation of Bulk and Interface Defects in Sputtered-NiO_x-Based Planar Perovskite Solar Cells: A Facile Interfacial Engineering Strategy with Alkali Metal Halide Salts

Passivation of Bulk and Interface Defects in Sputtered-NiO_x-Based Planar Perovskite Solar Cells: A Facile Interfacial Engineering Strategy with Alkali Metal Halide Salts

Surface Passivation of Sputtered NiO_x Using a SAM Interface Layer to Enhance the Performance of Perovskite Solar Cells