Rene Asomoza

Characterization of indium-doped zinc oxide films deposited by pyrolytic spray with different indium compounds as dopants

The results of a systematic study of the electrical, optical, structural and surface properties of thin ZnO:In films are presented. The films were deposited by the spray pyrolysis technique. The spraying solution was zinc acetate diluted in methanol and the indium doping was achieved by adding indium acetate, indium nitrate and indium sulfate at different concentrations up to [In]/[Zn] = 3 at%. The films grown at low temperature show regular and uniformly smooth surfaces with no texturization. Films grown at high temperature show rough surfaces. All the films are polycrystalline and grow with a (101) preferred orientation. The electrical resistivity measured at room temperature shows a minima in all cases as a function of the substrate temperature. The lowest value, ρ = 2 × 10−3Ω cm, was obtained by doping with indium acetate at a [In]/[Zn] = 3 at% concentration. For films about 0.6 μm thick the average transmittance was better than 85%. A shift in the energy gap due to a variation in the carrier concentration was observed. This shift is explained with a model in which the Burstem-Moss effect and the electron-electron exchange interaction are considered.

Formation of pn Homojunction in Cu(InGa)Se2 Thin Film Solar Cells by Zn Doping

In this study, a pn homojunction was intentionally fabricated in the Cu(InGa)Se2 (CIGS) layer by Zn doping. For Zn doping of the CIGS layer, Zn was evaporated after CIGS formation, and a potential improvement in cell performance was confirmed by this technique. Furthermore, Zn diffusion into the CIGS film was investigated by secondary ion mass spectroscopy (SIMS). A conductivity-type conversion from p-type to n-type was studied by the measurement of the cross-sectional electron beam-induced current (junction EBIC: JEBIC) and the spectral response of solar cells. A conversion efficiency of 11.5% has been achieved using the Zn-doped CIGS layer without a buffer layer and by the formation of a pn homojunction in the CIGS absorber.

Production and characterisation of carbon nitride thin films produced by a graphite hollow cathode system

Abstract Carbon nitride thin films have been prepared by plasma enhanced chemical vapour deposition of CH 4 and N 2 gas mixtures, by chemical transport from a hollow graphite cathode. The deposits prepared on pieces of single crystal silicon substrates were characterised using FTIR, Raman, SEM, EDX, SIMS, X-ray and electron diffraction. Single, double and triple carbon nitrogen bonds were detected in the FTIR spectra; the relative intensities of the associated bands being a function of the plasma power and substrate bias. Elemental analysis of the deposit showed that the nitrogen content was ∼57 at%. A polycrystalline deposit identified as hexagonal β -C 3 N 4 was obtained at low substrate temperatures. The deposit was found to grow preferentially on scratch defects on the silicon substrate surface and was stable upon annealing under vacuum up to 700°C.

High-rate deposition of silicon thin-film solar cells by the hot-wire cell method

Abstract The hot-wire cell method has been developed to grow polycrystalline and amorphous Si thin films with relatively high growth rates of 0.4–3.0 nm s −1 . It was found that polycrystalline Si films can be obtained at substrate temperatures of 175–400°C without hydrogen dilution when the filament temperature is 2000–2100°C. Valency control has been carried out using PH 3 and B 2 H 6 . Up to now, high conductivities of 13 and 4 S cm −1 have been achieved for n- and p-type polycrystalline Si thin films, respectively. Superstrate-type polycrystalline Si and amorphous Si solar cells prepared with deposition rates of 0.4–1.0 nm s −1 showed efficiencies of 1.6 and 4.3% under AM1.5 illumination, respectively. We found by SIMS analysis that a high concentration of O and C atoms, of the order of 10 20 –10 21 cm −3 , is incorporated into the film, which limits the performance of the present cell.

Seasonal quality factor; 60 kWp PV system at north Mexico City

In the Research Center (CINVESTAV), located north Mexico City was evaluated 60 kWp photovoltaic (PV) system. The PV system energy performance ratio, so called “quality factor” are reported together with the measured solar irradiation, ambient and PV module temperatures. Quality factor defines the overall system performance with respect to the energy production, solar resource, and total effect of system losses. The electric grid-tied PV system consists of 240 PV modules of 250 Wp each, which are connected to 5 inverters to produce three phase AC. We describe the general PV system quality factor in a month basis for 2013. In spite of the different seasonal weather conditions and some inverter trouble, the calculated average quality factor was 91.75%. The averaged daily PV generated energy throughout the year was 258.9 kWh/day. The accumulated total generated energy during the year was 94,427.7 kWh. However, instead of using solar irradiance sensor at the array tilt angle, and taking in consideration the horizontal global irradiation, the quality factor reduces drastically to 83.56%.

POLY-SILICON THIN FILMS PREPARED BY LOW TEMPERATURE ALUMINUM-INDUCED CRYSTALLIZATION

P-type poly-Si thin films prepared by low temperature Aluminum-induced crystallization and doping are reported. The starting material was boron-doped a-Si:H prepared by PECVD on glass substrates. Aluminum layers with different thicknessess were evaporated on a-Si:H surface and conventional thermal annealing was performed at temperatures ranging from 300 to 550°C. XRD, SIMS, TEM and Hall effect measurements were carried out to characterize the annealed films. Results show that a-Si:H contacted with adequate Al could be crystallized at temperature as low as 300°C after annealing for 60 minutes. This material has high carrier concentration as well as high Hall mobility can be used as a p-layer or seed layer for thin film poly-Si solar cells. The technique reported here is compatible with PECVD process.

Fabrication of high stabilized efficiency a-Si solar cells by using SiH/sub 2/Cl/sub 2/ addition

We have applied SiH/sub 2/Cl/sub 2/ addition together with H/sub 2/ dilution to a-Si:H films and solar cells fabricated by mercury-sensitized photo-CVD. It was observed by SIMS measurements that Cl was incorporated into a-Si:H films over 10/sup 18/ atom/cm/sup 3/, even at the flow rate ratio of 0.01(SiH/sub 2/Cl/sub 2/ to SiH/sub 4/). Furthermore, it was found that excess Cl incorporated in a-Si:H films had been removed by H/sub 2/ dilution. With H/sub 2/ dilution, we could control the excess acceptor states of a-Si:H films grown by SiH/sub 2/Cl/sub 2/ addition and when we applied them to the i-layer of a-Si solar cells, quantum efficiencies increased at all wavelength region and especially at middle wavelength region which is sensible to the electric field weakening of the i-layer by light induced degradation. As a result, we have achieved a high stabilized efficiency of 9.0% for an 1 cm/sup 2/ single-junction a-Si:H solar cell.

Improvement of a-Si:H solar cell characteristics by means of a boron-carbon window layer

Thin film p-i-n-type hydrogenated amorphous silicon solar cells have been obtained using the conventional technique of plasma-enhanced chemical vapor deposition employing only boron and carbon as a p-layer window. This layer was obtained using the common gas sources CH4 and B2H6 (methane and diborane) and has properties similar to those of a p-type semiconductor such as a-Si:C (amorphous silicon carbide). Auger electron spectroscopy and secondary ion mass spectroscopy were employed to verify the boron carbon deposition on single-crystalline silicon. Solar cells with a total thickness of only 300 nm have a short-circuit current density of 13.3 mA/cm2 with an open-circuit voltage of 870 mV. The efficiency of the solar cells was considerably increased when the B-C window layer was applied.