Z.Q. Ma

Preparation of ITO/SiOx/n-Si solar cells with non-decline potential field and hole tunneling by magnetron sputtering

Complete photo-generated minority carriers quantum tunneling device under AM1.5 illumination is fabricated by depositing tin-doped indium oxide (ITO) on n-type silicon to form a structure of ITO/SiOx/n-Si heterojunction. The work function difference between ITO and n-Si materials essentially acts as the origin of built-in-field. Basing on the measured value of internal potential (Vbiu2009=u20090.61u2009V) and high conversion efficiency (9.27%), we infer that this larger photo-generated holes tunneling occurs when a strong inversion layer at the c-Si surface appears. Also, the mixed electronic states in the ultra-thin intermediate region between ITO and n-Si play a defect-assisted tunneling.

Low temperature characteristic of ITO/SiOx/c-Si heterojunction solar cell

Based on the temperature-dependent measurements and the numerical calculation, the temperature response of the photovoltaic parameters for a ITO/SiO x /c-Si heterojunction solar cell have been investigated in the ascending sorting of 10–300 K. Under unique energy concentrated photon irradiation with the wavelength of 405 nm and power density of 667 mW cm−2, it was found that the short-circuit current (I SC) was nonlinearly increased and the open-circuit voltage (V OC) decreased with temperature. The good passivation of the ITO/c-Si interface by a concomitant SiO x buffer layer leads to the rare recombination of carriers in the intermediate region. The inversion layer model indicated that the band gap of c-silicon was narrowed and the Fermi level of n-type silicon () tended to that of the intrinsic Fermi level () (in the middle of band gap) with the increase of the temperature, which lessened the built-in voltage (V D) and thus the V OC. However, the reduction by 90% of V OC is attributed to the shift of in c-silicon rather than the energy band narrowing. Through the analysis of the current–voltage relationship and the data fitting, we infer that the series resistance (R s) is not responsible for the increase of I SC, but the absorption coefficient and the depletion-width of c-silicon are the causes of the enhancing I SC. Mostly, the interaction of the photon-generated excess cold hole and the acoustic phonon in n-Si would influence the variation of I ph or I SC with temperature.

Structural defects and recombination behavior of excited carriers in Cu(In,Ga)Se2 solar cells

The carriers’ behavior in neutral region (NTR) and space charged region (SCR) of Cu(In,Ga)Se2 thin film based solar cells has been investigated by temperature dependent photoluminescence (PL-T), electroluminescence (EL-T) and current-voltage (IV-T) from 10 to 300 K. PL-T spectra show that three kinds of defects, namely VSe, InCu and (InCu+VCu), are localized within the band gap of NTR and SCR of CIGS layer, corresponding to the energy levels of EC-0.08, EC-0.20 and EC-0.25 eV, respectively. The InCu and (InCu+VCu) deep level defects are non-radiative recombination centers at room temperature. The IV-T and EL-T analysis reveals that the injection modes of electrons from ZnO conduction band into Cu(In,Ga)Se2 layer are tunneling, thermally-excited tunneling and thermionic emission under 10-40, 60-160, and 180-300 K, respectively. At 10-160 K, the electrons tunnel into (InCu+VCu) and Vse defect levels in band gap of SCR and the drifting is involved in the emission bands at 0.96 and 1.07 eV, which is the direc...

Potentiality of delocalized states in indium-involved amorphous silicon oxide

In this short report, the specific molecular coacervate and two kinds of quantum states in indium-involved amorphous silicon oxide [a-SiOx(In)] are studied. The a-SiOx(In) layer is prepared by the magnetron sputtering process for indium tin oxide (ITO) films deposited on n-type silicon substrates, which has been predicted by molecular dynamics simulation and density function theory calculation. The results have been applied to the interpretation of the electronic structure and hole tunneling transport in ITO-SiOx/n-Si photovoltaic (PV) devices. The most significant achievement is that there is either a transition level at 0.30u2009eV for p-type conductive conversion or an extra level at Evu2009+u20094.60u2009eV induced by In-O-Si bonding, denoted as molecular orbital levels, within the dielectric amorphous oxide (a-SiOx). The cognizance is crucial for the concepts of passivation, tunneling, selective contact, inversion, and useful defects in modern PV devices.

Fabrication of Highly Oriented TiO2 Nanotube Arrays and their Application in DSSC

A two-electrode technique has been employed to anodize Ti foils for obtaining highly oriented TiO2 nanotube (NT) arrays. The morphology of the NT arrays was characterized by scanning electron microscope. With increasing anodization time, the lengths and diameters of TiO2 NT arrays was added from 6.7 to 19.5 μm, and 90 to 110 nm, respectively. As confirmed by X-ray diffraction and Raman spectra, the as-anodized TiO2 NTs were amorphous but transformed into anatase phase after thermal annealing at 450°C for 3 hours. Reflectance spectrum of TiO2 NT arrays showed that the layer with longer NTs can lower the reflectance in the visible spectrum because of the stronger light scattering effects of NTs, thus enhancing light harvesting from NTs. Dye-sensitized solar cells were fabricated using TiO2 NT arrays (tube-lengths: 6.7, 12.8, 16.3 and 19.5 μm). The characteristic of photocurrent density-voltage (J-V) showed that higher conversion efficiencies can be achieved with the longer NTs.

Thickness impact of aluminum and silicon on bow of silicon solar cells

As the thickness of silicon solar cells becomes thinner, the cells are susceptible to bow because of the metallization of metal and semiconductor on the front and rear contact. In this work, the thickness impacts of aluminum and silicon on bow of the solar cell have been investigated with the perspective of deformation and strain.

Effect of deposition pressure on structural and optical properties of scandium-doped ZnO thin film prepared by sputtering

Microstructural, optical and electrical properties of Sc-doped ZnO films grown by RF magnetron sputtering at room temperature were investigated. The deposition pressure was varied from 0.3 to 2.0 Pa. XRD spectra indicated that the (100) peak of the film weakened as the reaction pressure decreased and the (110) peak strengthened at a preferred pressure, 0.3Pa. Compare with (100) and (110) peaks, the intensity of (002) peak was relative weak. The strain in the film was investigated. The average transmittance of these films was above 90% in the wavelength range from 400 to 800 nm, while decreased in short wavelength region due to the light scattering. More significantly, various optical band gap of the films were found correspond with different pressure. The causation might be due to the Burstein-Moss effect.

The first-principles study of Al adsorption on Si(001)2×1

First-principles calculations have been performed to study the adsorption of Aluminium(Al) on the Si(001)2×1 surface. The optimized geometries and electronic structures of the adsorption system were investigated. The adsorption energy at various adsorption coverages(Θ) from half a monolayer(ML) to one monolayer has been calculated. The most stable adsorption sites were consequently determined to be HH site and T3-T4 site, respectively. There is obvious evidence that the asymmetric aspect of the Si-Si dimer becomes the symmetric one which has been observed at the coverage of 0.5ML or 1ML. In addition, the bond length of Si-Si was found to be considerably elonged upon the Al adsorption. The work function calculations have shown that the aspect of work-function change for the Si(001) surface due to the adsorption of Al is different from that of the alkali metals adsorption reported in some previous works. The surface formation energy was also calculated. The absolute value of the surface formation energy was found to decrease with increasing coverage indicating that 1ML is not a saturation coverage. In order to shed light on the nature of the Al-Si bond and the character of silicon surface, the density of states and band structure of the system were calculated.

Parameter optimization of silicon solar cell back surface field (BSF) formation

The BSF of mono-crystal silicon cell is studied in this paper. It simply states the principle and formation process of BSF, and studies the evenness of BSF. In the experiment, we analyze BSF formed by taking different sintering temperature, heating rate and setting different time, develop by chemical reagent and observe at high magnification scope, analyze and get the optimal parameters of forming even BSF and further improve conversion efficiency of silicon chips.