BiSI (indirect band gap = 1.57 eV) is a recently discovered photoelectrode material possessing promising optical properties for use in alternative thin film solar cells. In this work, we study the effects of selenium doping on BiSI film properties and also demonstrate the incorporation of BiS1–xSexI films into both electrochemical and solid state solar cells. Tuning the band gap of BiS1–xSexI by substituting selenium for sulfur was accomplished by substituting various amounts of SeO2 for thiourea in the BiSI spray pyrolysis precursor solutions. This strategy was employed to reduce the direct band gap of BiS1–xSexI films from 1.63 eV to as low as 1.48 eV, as measured by UV–vis–NIR diffuse reflectance spectroscopy for x = 0.4. Both electrochemical and solid state solar cell devices utilizing n-BiSI as the light absorbing material demonstrated open circuit voltages of nearly 0.4 V. The electrochemical devices showed much higher short circuit currents and power conversion efficiencies than the solid state dev...

n-BiSI Thin Films: Selenium Doping and Solar Cell Behavior

The development of improved solar energy conversion materials is critical to the growth of a sustainable energy infrastructure in the coming years. We report the deposition of polycrystalline BiSI thin films exhibiting promising photoelectrochemical properties on both metal foils and fluorine-doped tin-oxide-coated glass slides using a single-source chemical spray pyrolysis technique. Their strong light absorption in the visible range and well-crystallized layered structure give rise to their excellent photoelectrochemical performance through improved electron-hole generation and separation. The structure and surface composition of the films are dependent on deposition temperature, resulting in dramatic differences in performance over the temperature range studied. These results reveal the potential of n-BiSI as an alternative thin film solar energy conversion material and may stimulate further investigation into V-VI-VII compounds for these applications.

BiSI Micro-Rod Thin Films: Efficient Solar Absorber Electrodes?

A sonochemical method for direct preparation in water of a gel consisted of nanocrystalline antimony sulfoiodide (SbSI) nanowires is presented for the first time. The product was characterized by using techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, optical diffuse reflection spectroscopy and IR spectroscopy. The electrical properties of the fabricated nanomaterial have been investigated, too. The nanowires are a semiconducting ferroelectric with Curie constant equal C = 1.41(14) × 104 K and Curie temperature equal TC = 293.0(2) K. The indirect allowed energy band gap of this material is EgIa = 1.880(2) eV. Such prepared SbSI nanowires have optical and electrical properties suitable for ferroelectric nanosensors.

Fabrication and characterization of SbSI gel for humidity sensors

An analysis of the P2S6 cluster electronic structure and its comparison with the crystal valence band in the paraelectric and ferroelectric phases has been done by first-principles calculations for Sn2P2S6 ferroelectrics. The origin of ferroelectricity has been outlined. It was established that the spontaneous polarization follows from the stereochemical activity of the electron lone pair of tin cations, which is determined by hybridization with P2S6 molecular orbitals. The chemical bonds covalence increase and rearrangement are related to the valence band changes at transition from the paraelectric phase to the ferroelectric phase.

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Electronic Structure and Phase Transition in Ferroelectic Sn2P2S6 Crystal

Sb1- x Bix SI, an isostructural material with the well-known quasi-1D SbSI, possesses good semiconductive and ferroelectric properties but is not applied in solar cells. Herein, solar cells based on alloyed Sb0.67 Bi0.33 SI (ASBSI) as a light harvester are fabricated. ASBSI is prepared through the reaction of bismuth triiodide in N,N-dimethylformamide solution with an antimony trisulfide film deposited on a mesoporous (mp)-TiO2 electrode via chemical bath deposition at 250 °C under an argon or nitrogen atmosphere; the alloy exhibits a promising bandgap (1.62 eV). The best performing cell fabricated with poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] as the hole-transporting layer shows 4.07% in a power conversion efficiency (PCE) under the standard illumination conditions of 100 mW cm-2 . The unencapsulated cells exhibit good comprehensive stability with retention of 92% of zjr initial PCE under ambient conditions of 60% relative humidity over 360 h, 93% after 1 sun illumination for 1254 min, and 92% after storage at 85 °C in air for 360 h.

Efficient Solar Cells Employing Light-Harvesting Sb 0.67 Bi 0.33 SI

XPS and electronic structure of quasi-one-dimensional BiSI crystals

The electronic structure of the ferroelectric Sn 2 P 2 S 6 single crystal is studied by X-ray photoelectron spectroscopy in both paraelectric and ferroelectric phases. The spectra were measured with monochromatized Al Kα radiation in the energy range 0–1400 eV. Experimental energies are compared with the results of theoretical ab initio calculations of the molecular model of the crystal. The electronic structure of the valence band (VB) is revealed. Ferroelectric phase transition changes atom's charge and bonds strength, electronic structure of VB, core levels (CL) lines width and chemical shifts for the Sn, P and S states which are crystallographic plane-dependent.

XPS of Electronic Structure of Ferroelectric Sn2P2S6 Crystals

The form and electronic structure of the valence band (VB) of the ferroelectric SbSI crystal was calculated by solving the HartreenFocknRoothaan matrix equation. The diagonal eigenvalue matrix " gives the electron state energies. These energies were also studied experimentally by PHI 5700 / 660 Physical Electronics Spectrometer using Al Kfi monochromatic radiation (1486.6 eV) as the excitation source. The spectrum of the VB electronic levels was approximated by the Gauss functions. The form of the VB depends on the width of the Gauss function and the number of SbSI molecules, which were taken into account in the model of SbSI crystal. The obtained theoretical density of states and the VB form of SbSI crystal is close to the experimental one.

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ELECTRONIC STRUCTURE OF VALENCE BAND OF FERROELECTRIC SbSI CRYSTALS

The paper presents the X-ray photoelectron spectra (XPS) of the valence band (VB) and of the core levels (CL) of uniaxial ferroelectric Sn2P2S6 single crystals from different crystallographic planes in both paraelectric and ferroelectric phases. The XPS were measured with monochromatized Al K radiation in the energy range 0n1400 eV. The VB consists of v e bands with the maxima between 3.3 eV and 14.5 eV below the Fermi level. Experimental energies of the VB and core levels are compared with the results of theoretical ab initio calculations of the molecular model of the Sn2P2S6 crystal. The electronic structure of the VB is revealed. Ferroelectric phase transition changes the atom’s charge and strength of the bonds, electronic structure of VB, width of CL lines and chemical shifts for the Sn, P and S states which are crystallographic plane-dependent.

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X-Ray Photoelectron Spectroscopy of Sn2P2S6 crystals.

The paper presents the X-ray photoelectron spectra (XPS) of the valence band (VB) and of the principal core levels (CL) from the (010) and (001) plane axes for the quasi-one-dimensional TlInSe2 single crystal. The XPS were measured with monochromatized Al Kfi radiation in the energy range of 0n1400 eV at room and 393 K temperature. The VB is located 0.6n 10 eV below the Fermi level. Experimental energies of the VB and CL are compared with the results of quantum mechanical ab initio calculations of the molecular model of the TlInSe2 crystal. The electronic structure of the VB and CL is described theoretically by quantum mechanical HartreenFock calculations. The surface and bulk atoms inuence the shape of the VB and CL, which is crystallographic plane dependent. The chemical shifts in the TlInSe2 crystal for the Tl, In, and Se states are obtained.

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V. Nelkinas

Papers

XPS and electronic structure of quasi-one-dimensional BiSI crystals

XPS of Electronic Structure of Ferroelectric Sn2P2S6 Crystals

ELECTRONIC STRUCTURE OF VALENCE BAND OF FERROELECTRIC SbSI CRYSTALS

X-Ray Photoelectron Spectroscopy of Sn2P2S6 crystals.

XPS AND ELECTRONIC STRUCTURE OF TlInSe2 CRYSTALS