Surface photovoltage phenomena: theory, experiment, and applications

Kronik, Leeor; Shapira, Yoram

doi:10.1016/s0167-5729(99)00002-3

Cited by 1,518 publications

(847 citation statements)

References 611 publications

(1,189 reference statements)

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“…• H and He not detectable 129 • Damage and decomposition of soft and metastable materials 131 • Preferential sputtering during depth-profiling can remove more volatile components and change composition 30 • Beam-induced changes in oxidation state 129 • Binding energy shift due to charge accumulation, as well as junction and surface photovoltage 129,132 • Gas-phase surface contaminants can occur 129 Auger electron spectroscopy (AES) Sample irradiated with 3-20 keV electrons, ejecting core-level electrons in atoms and creating vacancies. Relaxation of outer electron to vacancy results in emission of Auger electron.…”

Section: Page 10 Of 39 Acs Paragon Plus Environment Chemistry Of Matementioning

confidence: 99%

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Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

et al. 2017

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ABSTRACT:Recently, there has been an explosive growth in research based on hybrid lead-halide perovskites for photovoltaics owing to rapid improvements in efficiency. The advent of these materials for solar applications has led to widespread interest in understanding the key enabling properties of these materials. This has resulted in renewed interest in related compounds and a search for materials that may replicate the defect-tolerant properties and long lifetimes of the hybrid lead-halide perovskites. Given the rapid pace of development of the field, the rises in efficiencies of these systems have outpaced the more basic understanding of these materials. Measuring or calculating the basic properties, such as crystal/electronic structure and composition, can be challenging because some of these materials have anisotropic structures, and/or are composed of both heavy metal cations and volatile, mobile, light elements. Some consequences are beam damage during characterization, composition change under vacuum, or compound effects, such as the alteration of the electronic structure through the influence of the substrate. These effects make it challenging to understand the basic properties integral to optoelectronic operation. Compounding these difficulties is the rapid pace with which the field progresses. This has created an ongoing need to continually evaluate best practices with respect to characterization and calculations, as well as to identify inconsistencies in reported values to determine if those inconsistencies are rooted in characterization methodology or materials synthesis. This article describes the difficulties in characterizing hybrid lead-halide perovskites and new materials, and how these challenges may be overcome. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 challenges discussed. The focus in this article is on crystallography, composition measurements, photoemission spectroscopy and calculations on perovskites and new, related absorbers. We suggest how some of the important artifacts could be avoided and how the reporting for each technique could be streamlined between groups to ensure reproducibility as the field progresses.

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Section: Page 10 Of 39 Acs Paragon Plus Environment Chemistry Of Matementioning

confidence: 99%

“…132,168,169 These effects are common in the semiconductors used in photovoltaic applications. In particular, the excitation energies used for XPS/UPS measurements may produce a sufficient amount of free charge carriers to result in a surface photovoltaic effect and change the surface band bending.…”

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Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

et al. 2017

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“…31 SPS uses a semitransparent Kelvin probe that contactlessly probes the surface potential change of an illuminated film (Figure 1) versus the excitation energy. 32,33 Measurable signals can be due to motion of free charge carriers through the film or the interface, due to polarization of charge Figure 1. Geometry of SPV measurement and example spectra.…”

Section: ■ Introductionmentioning

confidence: 99%

P3HT:PCBM Bulk-Heterojunctions: Observing Interfacial and Charge Transfer States with Surface Photovoltage Spectroscopy

et al. 2014

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Surface photovoltage (SPV) spectra are reported for separate films of (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) and for regioregular and regiorandom poly(3-hexylthiophene) (P3HT):PCBM bulk heterojunctions, as a function of wavelength, film thickness, thermal annealing, and substrate. In PCBM films, two photovoltage features are observed at 1.1–1.4 eV (F1) and 1.4–2.3 eV (F2), which are assigned to excitation of charge transfer states at the interface (F1) and in the bulk (F2) of the film. In BHJ films, five different photovoltage features are observed at 0.75–0.9 eV (F1), 0.9–1.3 eV (F2), 1.3–1.8 eV (F3), 1.8–2.0 eV (F4), and 2.0–2.4 eV (F5). This data can be analyzed on the basis of optical absorbance and fluorescence spectra of the films, and using SPV spectra for PCBM and P3HT only films, and for a BHJ film containing P3HT nanofibers for comparison. SPV features are assigned to states at the polymer–substrate interface (F1 and F2), the P3HT:PCBM charge transfer state (F3), the self-ionized (CT) state of P3HT (F4), and the band gap transition of P3HT (F5). This interpretation is also consistent with molecular orbital energy diagrams and electron microscopy-derived topological maps of the films. Photovoltage sign and substrate dependence can be understood with the depleted semiconductor model. Features F1–4 are caused by polarization of electrostatically bound charge pairs by the built-in electric field at the substrate–BHJ interface, whereas F5 is due to transport of free charge carriers through the film and through the substrate film interface. This work will promote the understanding of photochemical charge generation and transport in organic photovoltaic films.

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“…In SPS, a semi-transparent Kelvin electrode measures the contact potential difference (CPD) of an illuminated photocatalyst film (Fig. 25) as a function of the excitation energy [187,188]. The measured photovoltage (ΔCPD) is produced by the transfer of free charge carriers or polarization of bound charge carrier pairs (polarons) in the sample [189][190][191].…”

Section: Measuring Photovoltage In Nanoscale Photocatalystsmentioning

confidence: 99%

Nanoscale Effects in Water Splitting Photocatalysis

Osterloh

2015

Topics in Current Chemistry

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From a conceptual standpoint, the water photoelectrolysis reaction is the simplest way to convert solar energy into fuel. It is widely believed that nanostructured photocatalysts can improve the efficiency of the process and lower the costs. Indeed, nanostructured light absorbers have several advantages over traditional materials. This includes shorter charge transport pathways and larger redox active surface areas. It is also possible to adjust the energetics of small particles via the quantum size effect or with adsorbed ions. At the same time, nanostructured absorbers have significant disadvantages over conventional ones. The larger surface area promotes defect recombination and reduces the photovoltage that can be drawn from the absorber. The smaller size of the particles also makes electron-hole separation more difficult to achieve. This chapter discusses these issues using selected examples from the literature and from the laboratory of the author.

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Surface photovoltage phenomena: theory, experiment, and applications

Cited by 1,518 publications

References 611 publications

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

P3HT:PCBM Bulk-Heterojunctions: Observing Interfacial and Charge Transfer States with Surface Photovoltage Spectroscopy

Nanoscale Effects in Water Splitting Photocatalysis

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