High precision differential measurement of surface photovoltage transients on ultrathin CdS layers

Dittrich, Th.; Bönisch, S.; Zabel, P.; Dube, Sangeeta

doi:10.1063/1.3020757

Cited by 36 publications

(23 citation statements)

References 12 publications

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“…To investigate photochemical charge transfer in CuBi 2 O 4 nanoparticles, Surface Voltage Spectroscopy (SPS) was employed. 29,30 In this technique, a light-induced change of the contact potential difference (CPD, versus gold Kelvin probe) of a sample film is recorded as a function of the irradiation wavelength/energy ( Figure S1). 31 Depending on the direction of charge transport, this produces either positive or negative photovoltage.…”

Section: Resultsmentioning

confidence: 99%

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

et al. 2016

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a As a visible light active p-type semiconductor, CuBi2O4 is of interest as a photocatalyst for the generation of hydrogen fuel from water. Here we present the first photovoltage and photocatalytic measurements on this material and DFT results on its band structure. Single crystalline CuBi2O4 nanoparticles (25.7 ± 4.7 nm) were synthesized from bismuth and cupric nitrate in water under hydrothermal conditions. Powder X-ray diffraction (XRD) confirms the CuBi2O4 structure type and UV-Vis spectroscopy observes a 1.75 eV optical band gap. Surface photovoltage (SPV) measurements on CuBi2O4 nanoparticle films on fluorine doped tin oxide yield 0.225 V positive photovoltage at >1.75 eV photon energy confirming holes as majority carriers. The photovoltage is reversible and limited by light absorption. When dispersed in 0.075 M aqueous potassium iodide solution, the CuBi2O4 particles support photochemical hydrogen evolution of up to 16 µmol h-1 under ultraviolet but not under visible light. Based on electrochemical scans, CuBi2O4 is unstable towards reduction at -0.2 V, but pH-dependent photocurrents of 6.45 A cm -2 with an onset potential of +0.75 V vs. NHE can be obtained with 0.01 M Na2S2O8 as a sacrificial electron acceptor. The photoelectrochemical properties of CuBi2O4 can be explained on the basis of the band structure of the material. DFT calculations show the valence and conduction band edges to arise primarily from the combination of O 2p and Cu 3d orbitals, respectively, with additional contributions from Cu 3d and Bi 6s orbitals just below the Fermi level. Trapping of photoelectrons in the Cu 3d band is the cause for reductive photocorrosion of the material, while the p-type conductivity arises from copper vacancy states near the VB edge. These findings provide an improved understanding of the photophysical properties of p-CuBi2O4 and its limitations as a proton reduction photocatalyst.A) The DFT+U electronic band structures of (left) pristine CuBi2O4 and (right) VCu -CuBi2O4. The Fermi level (EF) is set at 0 eV. The presence of VCu leads to partial occupation of the bands around the VB edge. This gives rise to p-type behavior in CuBi2O4. B) The DFT+U projected density of states of VCu -CuBi2O4.

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Section: Resultsmentioning

confidence: 99%

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

et al. 2016

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“…The x - and y -signals begin at photon energies between 0.9 and 1.0 eV and reach maxima of −0.65 and 0.24 mV at 1.32 and 1.20 eV, respectively. The present case of a negative sign of the x -signal together with a positive sign of the y -signal can be interpreted as photogenerated electrons being preferentially separated towards the internal interface [19]. …”

Section: Resultsmentioning

confidence: 99%

Junction formation of Cu₃BiS₃ investigated by Kelvin probe force microscopy and surface photovoltage measurements

Mesa¹,

Chamorro‐Coral²,

Vallejo³

et al. 2012

Beilstein J. Nanotechnol.

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SummaryRecently, the compound semiconductor Cu3BiS3 has been demonstrated to have a band gap of ~1.4 eV, well suited for photovoltaic energy harvesting. The preparation of polycrystalline thin films was successfully realized and now the junction formation to the n-type window needs to be developed. We present an investigation of the Cu3BiS3 absorber layer and the junction formation with CdS, ZnS and In2S3 buffer layers. Kelvin probe force microscopy shows the granular structure of the buffer layers with small grains of 20–100 nm, and a considerably smaller work-function distribution for In2S3 compared to that of CdS and ZnS. For In2S3 and CdS buffer layers the KPFM experiments indicate negatively charged Cu3BiS3 grain boundaries resulting from the deposition of the buffer layer. Macroscopic measurements of the surface photovoltage at variable excitation wavelength indicate the influence of defect states below the band gap on charge separation and a surface-defect passivation by the In2S3 buffer layer. Our findings indicate that Cu3BiS3 may become an interesting absorber material for thin-film solar cells; however, for photovoltaic application the band bending at the charge-selective contact has to be increased.

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“…[14][15][16] In this case, undesirable noise often appeared within the first few microseconds, 19 as shown in Figure 3 (red circles). The origin of this system noise should be analyzed first.…”

Section: A Origin Of the System Noise In One-probe Configurationmentioning

confidence: 91%

“…Hereafter, this coherent noise is referred to as system noise, and its origin is the focus of the present work. In this work, the traditional one-probe configuration for TPV measurement [14][15][16] (only one electrode was monitored by an oscilloscope, and the other was grounded) was promoted to the novel two-probe configuration, which allows for TPV measurements at up to 1.5 GHz (bandwidth) and 50 GS/s (sampling rate) without any degradation in the noise level. This two-probe measuring system is able to measure the TPV of either electrode of a typical sandwich-structured photoelectronic device (a thin photosensitive semiconductor layer sandwiched between two electrodes) independently, where one electrode is transparent to allow ambient illumination into the active layer independently.…”

Section: Introductionmentioning

confidence: 99%

High-bandwidth, high-sampling-rate, low-noise, two-probe transient photovoltage measuring system

Chen

2015

Review of Scientific Instruments

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In this article, we present a two-probe configuration for measuring transient photovoltage (TPV) signals from photo-electronic semiconductor devices. Unlike in a conventional one-probe system, the two electrodes of the devices under test in this study are both monitored in our new measuring system, giving rise to a significantly enhanced signal-to-noise ratio. Tentative experimental data ob tained from N, N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine-based organic semiconductor devices show that the bandwidth and the sampling rate of the system reach 1.5 GHz and 50 GS/s, respectively, without degradation of the noise level. In addition, the study of TPV signals on each individual electrode is allowed. The TPV values measured by the two individual probes are not identically equal to half of the differential TPV and will not cancel each other out as expected. This abnormal phenomenon is due to the photoelectric response of the photo-electronic material. This novel two-probe TPV measuring technique and abnormal TPV behavior might be useful for studying more dynamic processes in photo-electronic semiconductors.

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High precision differential measurement of surface photovoltage transients on ultrathin CdS layers

Cited by 36 publications

References 12 publications

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

Junction formation of Cu₃BiS₃ investigated by Kelvin probe force microscopy and surface photovoltage measurements

High-bandwidth, high-sampling-rate, low-noise, two-probe transient photovoltage measuring system

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High precision differential measurement of surface photovoltage transients on ultrathin CdS layers

Cited by 36 publications

References 12 publications

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi2O4 nanocrystals

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi2O4 nanocrystals

Junction formation of Cu3BiS3 investigated by Kelvin probe force microscopy and surface photovoltage measurements

High-bandwidth, high-sampling-rate, low-noise, two-probe transient photovoltage measuring system

Contact Info

Product

Resources

About

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

Electronic structure, photovoltage, and photocatalytic hydrogen evolution with p-CuBi₂O₄ nanocrystals

Junction formation of Cu₃BiS₃ investigated by Kelvin probe force microscopy and surface photovoltage measurements