Papers by Keyword: Surface Photovoltage

Abstract: In this paper, α-Fe₂O₃ photocatalyst with high photocatalytic activity (IL-α-Fe₂O₃) was fabricated via hydrothermal routine using 1-ethyl-3- methylimidazolium dihydrophosphate ([EMIm]H₂PO₄). The specific surface area, structure, the photo-induced charge separation rate were characterized by Brunauer-Emmett-Teller (BET) measurements, X-ray diffraction (XRD), and surface photovoltage spectroscopy (SPS), respectively. The results show that adding ([EMIm]H₂PO₄ into the synthetic system alters the specific surface parameters and photo-induced charge separation rate. The photocatalytic activity for decolorization of methyl orange (MO) solution was investigated. The results show that the photocatalytic activity of IL-α-Fe₂O₃ is more than 2.5 times that of the reference α-Fe₂O₃ and the underlying mechanisms are discussed.

Abstract: A selective emitter structure is a promising approach to improve the cell efficiency of industrial type silicon solar cells by minimizing the losses at the front surface and in the emitter. Selective emitters can be produced by numerous processing sequences, resulting in different doping profiles. This paper focuses on the analysis of emitter formation for bifacial solar cell application. In this research, liquid phosphorus oxy-trichloride (POCl₃) has been used as a diffusion source for emitter formation. The diffusion temperature was varied from 800 to 900 °C in order to determine an optimum diffusion profile. In this study, the mask-free diffusion process forms diffused emitter on both side of Si wafer. In order to determine the emitter characteristics, the sheet resistance of Si wafer after POCl₃ diffusion process was measured using a four-point probe. Based on the sheet resistance value of ~47 ohm/sq, the emitter has been classified as heavily-doped emitter. The performance analysis using surface photovoltage (SPV) and spectral response presents a diffusion length of 2.19 μm. The POCl₃-diffusion and screen printed Al-BSF led to bifacial solar cells with a front surface efficiency of 12.8 % and back surface efficiency of 5.08 %.

Abstract: Motivated by the importance of the oxidized silicon layers, we have studied the surface photovoltage (SPV) transients in nanoislands of Ge_xSi_1x on silicon and oxidized Si surfaces. It is shown that the SPV decays can be approximated by the stretched-exponential form, with the β values ranging from 0.3 to 0.6 for the islands grown on oxide-covered Si substrates and from 0.5 to 1 for the ones placed on bare Si. On this basis, a simple qualitative model is proposed that takes into account a donor-and acceptor-like interface states at the GeSi/SiO₂ and Si/SiO₂ interface, which act as recombination centers with densities dependent on the GeSi coverage. These results can be used to improve the functionality of photoelectric devices based on Ge/Si.

Abstract: For more than 20 years, the application of ozone dissolved in pure deionised water (DIW-O₃) has been investigated for wafer-cleaning and resist stripping applications in the semiconductor industry [, , ]. To reduce chemical consumption and disposal costs as well as to improve cleaning efficiency, DIW-O₃ is used in semiconductor wet cleaning processes as an alternative to traditional sulphuric acid peroxide (H₂SO₄/H₂O₂) [] and RCA [] cleans. Silicon solar cell fabrication includes multiple wet cleaning steps involving large amounts of chemicals. In Si substrate manufacturing the wet-chemical oxidation of substrate surface is used mainly for three purposes: (i) the removal of surface contamination and surface micro-roughness by different cleaning and smoothing procedures in H₂O₂ containing solutions (RCA I and RCA II) [5], in H₂SO₄/H₂O₂ [4], (ii) the preparation of hydrophilic surfaces for subsequent layer deposition [,] and (iii) the fabrication of thin oxide layers []. Chemical consumption could be reduced by replacing some of these chemicals with a mixture of pure deionised water with dissolved ozone for cleaning and surface conditioning. The kinetics of wet-chemical oxidation in DIW-O₃ were recently investigated by ellipsometrical measurements of oxide thicknesses (ox>) [3,6,7], by SPV-measurements [7,], by contact angle measurements as well as by quasi-steady-state photo conductance (QSSPC) measurements [7].

Abstract: The crystallization of anatase from amorphous TiO₂ nanotube arrays (TNTs) has been carried out by annealing in air and hydrothermal treatment in water. The morphology and crystalline phase of obtained TNTs membranes were detailedly characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The surface electronic structure and photoelectrochemical properties (PEC) of TNTs obtained by different crystallization methods were investigated. The results show that the TNTs electrode crystallized by hydrothermal treatment method demonstrate a broader surface photovoltage response range and higher photoelectrochemical properties than that of TNTs electrode directly annealed in air due to effective Ti³⁺ sites.

Abstract: The effect of morphology on the stability of Cu2O remains a great challenge. We have synthesized two types of samples in cube crystal structure with about 700 nm by a facile reduction route, which were investigated by X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Energy- dispersive X-ray (EDX) and surface photovoltage spectroscopy (SPS). It is noteworthy that one sample prepared using polyethylene glycol (PEG) as template was oxidized in air, but another template with glucose was stable in air. The testing results demonstrate that the differences of Cu2O morphology apparently affect its stability. In addition, we analyzed the effect of surface oxidation on the SPV signal of the two samples.

Abstract: The fluorescent and photovoltaic properties of derivatives of selected substituted meso-phenylporphyrins were studied. It was found that the fluorescent intensity could be enhanced by the electron-donating substituent but weakened by the electron-withdrawing subsituent. The photovoltaic properties and charge transfer process of the compounds were investigated by surface photovoltage spectroscopy (SPS) techniques, which revealed that all the compounds are p-type semiconductors. The spectral bands of all porphyrins could be ascribed to π→π* transitions. Comparing with the fluorescent spectral showed that the stronger the fluorescence intensity of porphyrin was, the weaker the surface photovoltage intensity of it was.

Abstract: Effects of a kHz-frequency ultrasonic cleaning of silicon wafers on free carrier lifetimes and the photovoltage magnitude are addressed. It is found that the initial photovoltage decay, taken before ultrasonic treatments, can be fitted to a double-exponent form, exhibiting the involvement of shorter- and longer time recombination and trapping centers. The decay speeds up remarkably due to the treatment, and the rapid component of the decay grows at the expense of the slow component. It is also found that, before the treatment, the decay time is markedly non-uniform over the wafer surface, implying the existence of distributed sites affecting carrier lifetimes. The cleaning causes an overall smoothening of the lifetime distribution, which is accompanied by the above shortening. A likely explanation of the effects is based on two facts: (i) the cavitating bubbles are capable of locally removing the surface oxide layer affecting the dangling bonds on the bare Si surface, and (ii) the oxygen and hydrogen, decomposed in water at elevated pressures and temperatures occurring inside a cavitating bubble, can micro-precipitate the Si wafer thus affecting the recombination rate.

Abstract: On the principle of surface photovoltage (SPV) and photocatalysis, an approach was proposed and developed to evaluate a photocatalytical activity of catalysts from SPV intensity measurements. By using a model case of TiO₂ catalysts, the method was experimentally studied for determination and prediction of the activity by intensity of SPV responses as a parameter. It was found that the photocatalytical activity correlates well with the SPV value of catalysts. The SPV intensity as measuring parameter, with characteristics of quick, easy, non-destructive operation, may be applied efficiently to evaluate photocatalytical activity of solid materials such as mono/multi crystalline, film and particulate powder in various types, sizes and treatments.