Light-induced changes in diphasic nanocrystalline silicon films and solar cells

A series of diphasic nanocrystalline silicon films and solar cells was prepared using different hydrogen dilution ratios of silane by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). It was observed that after light soaking the open circuit voltage (V-oc) of the diphasic solar cells increased, while that of amorphous silicon solar cells decreased. Raman scattering spectroscopy was performed on the series of diphasic silicon films before and after light soaking. It was found that after light soaking the nanostruclures in the diphasic nanocrystalline silicon films were changed. Both the grain sizes and grain volume fraction reduced, while the grain boundary components increased. These results provide experimental evidence for the conjecture that the light-induced increase in V-oc of the diphasic nanocrystalline solar cells might be induced by the changes in the nanostructure of the intrinsic layer. (c) 2006 Elsevier B.V. All rights reserved.

Electron irradiation and thermal annealing effect on GaAs solar cells

This paper describes the effect of electron irradiation and thermal annealing on LPE AlGaAs/GaAs heterojunction solar cells with various p/n junction depths. The electron irradiation experiments were performed with energy of 3 MeV, fluences ranging from 1 x 10(14) to 5 x 10(15) e/cm(2). The results obtained demonstrate that the irradiation-induced degradation of performances of the cells is mainly in the short circuit current and could be mostly recovered by annealing at 260 degrees C for 30 min. Four electron traps, E-c - 0.24 eV, E-c - 0.41 eV, E-c - 0.51 eV, E-c - 0.59 eV, were found by DLTS analysis, only two shallow levels of which could be removed by the annealing. (C) 1998 Elsevier Science B.V. All rights reserved.

Thermal test and analysis of concentrator solar cells - art. no. 684117

Under high concentration the temperature of photovoltaic solar cells is very high. It is well known that the efficiency and performance of photovoltaic solar cells decrease with the increase of temperature. So cooling is indispensable for a concentrator photovoltaic solar cell at high concentration. Usually passive cooling is widely considered in a concentrator system. However, the thermal conduction principle of concentrator solar cells under passive cooling is seldom reported. In this paper, GaInP/GaAs/Ge triple junction solar cells were fabricated using metal organic chemical vapor deposition technique. The thermal conductivity performance of monolithic concentrator GaInP/GaAs/Ge cascade solar cells under 400X concentration with a heat sink were studied by testing the surface and backside temperatures of solar cells. The tested result shows that temperature difference between both sides of the solar cells is about 1K. A theoretical model of the thermal conductivity and thermal resistance of the GaInP/GaAs/Ge triple junction solar cells was built, and the calculation temperature difference between both sides of the solar cells is about 0.724K which is consistent with the result of practical test. Combining the theoretical model and the practical testing with the upper surface temperature of tested 310K, the temperature distribution of the solar cells was researched.

Silicon thin films prepared in the transition region and their use in solar cells

Diphasic silicon films (nc-Si/a-Si:H) have been prepared by a new regime of plasma enhanced chemical vapour deposition in the region adjacent of phase transition from amorphous to microcrystalline state. Comparing to the conventional amorphous silicon (a-Si:H), the nc-Si/a-Si:H has higher photoconductivity (sigma(ph)), better stability, and a broader light spectral response range in the longer wavelength range. It can be found from Raman spectra that there is a notable improvement in the medium range order. The blue shift for the stretching mode and red shift for the wagging mode in the IR spectra also show the variation of the microstructure. By using this kind of film as intrinsic layer, a p-i-n junction solar cell was prepared with the initial efficiency of 8.51 % and a stabilized efficiency of 8.01% (AM 1.5, 100 mw/cm(2)) at room temperature. (c) 2006 Published by Elsevier B.V.

Nanostructure in the p-layer and its impacts on amorphous silicon solar cells

The open circuit voltage (V-oc) of n-i-p type hydrogenated amorphous silicon (a-Si:H) solar cells has been examined by means of experimental and numerical modeling. The i- and p-layer limitations on V-oc are separated and the emphasis is to identify the impact of different kinds of p-layers. Hydrogenated protocrystalline, nanocrystalline and microcrystalline silicon p-layers were prepared and characterized using Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), optical transmittance and activation energy of dark-conductivity. The n-i-p a-Si:H solar cells incorporated with these p-layers were comparatively investigated, which demonstrated a wide variation of V-oc from 1.042 V to 0.369 V, under identical i- and n-layer conditions. It is found that the nanocrystalline silicon (nc-Si:H) p-layer with a certain nanocrystalline volume fraction leads to a higher V-oc. The optimum p-layer material for n-i-p type a-Si:H solar cells is not found at the onset of the transition between the amorphous to mixed phases, nor is it associated with a microcrystalline material with a large grain size and a high volume fraction of crystalline phase. (c) 2006 Elsevier B.V. All rights reserved.

Light-induced changes in diphasic nanocrystalline silicon films and solar cells

A series of diphasic nanocrystalline silicon films and solar cells was prepared using different hydrogen dilution ratios of silane by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). It was observed that after light soaking the open circuit voltage (V-oc) of the diphasic solar cells increased, while that of amorphous silicon solar cells decreased. Raman scattering spectroscopy was performed on the series of diphasic silicon films before and after light soaking. It was found that after light soaking the nanostruclures in the diphasic nanocrystalline silicon films were changed. Both the grain sizes and grain volume fraction reduced, while the grain boundary components increased. These results provide experimental evidence for the conjecture that the light-induced increase in V-oc of the diphasic nanocrystalline solar cells might be induced by the changes in the nanostructure of the intrinsic layer. (c) 2006 Elsevier B.V. All rights reserved.

Organic/inorganic hybrid solar cells based on SnS/SnO nanocrystals and MDMO-PPV

SnS/SnO heterojunction structured nanocrystals with zigzag rod-like connected morphology were prepared by using a simple two-step method. Bulk heterojunction solar cells were fabricated using the SnS/SnO nanocrystals blended with poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene) (MDMO-PPV) as the active layer. Compared with solar cells using SnS nanoparticles hybridized with MDMO-PPV as the active layer, the SnS/SnO devices showed better performance, with a power conversion efficiency higher by about one order in magnitude.

Microcrystalline silicon films and tandem solar cells prepared by triode PECVD

This paper investigates the effects of the diphasic structure on the optoelectronic properties of hydrogenated microcrystalline silicon (mu c-Si:H) films prepared in a triode three-chamber plasma-enhanced chemical vapor deposition (PECVD) system. The influences of boron-compensation doping on the dark-and photo-conductivity of mu c-Si:H films are also described. A tandem solar cell with an entirely mu c-Si:H p-i-n bottom cell and an a-Si:H top cell has been prepared with an initial conversion efficiency of 8.91% (0.126 cm(2), AM1.5, 100 mW/cm(2)).

Polycrystalline silicon thin films and solar cells prepared by rapid thermal CVD

Polycrystalline silicon (poly-Si) films(similar to 10 mu m) were grown from dichlorosilane by a rapid thermal chemical vapor deposition (RTCVD) technique, with a growth rate up to 100 Angstrom/s at the substrate temperature (T-s) of 1030 degrees C. The average grain size and carrier mobility of the films were found to be dependent on the substrate temperature and material. By using the poly-Si films, the first model pn(+) junction solar cell without anti-reflecting (AR) coating has been prepared on an unpolished heavily phosphorus-doped Si wafer, with an energy conversion efficiency of 4.54% (AM 1.5, 100 mW/cm(2), 1 cm(2)).

High efficiency AlxGa1-xAs/GaAs solar cells: Fabrication, irradiation and annealing effect

High efficiency AlxGa1-xAs/GaAs heteroface solar cells have been fabricated by an improved multi-wafer squeezing graphite boat liquid phase epitaxy (LPE) technique, which enables simultaneous growth of twenty 2.3 X 2.3cm(2) epilayers in one run. A total area conversion efficiency of 17.33% is exhibited (1sun, AM0, 2.0 x 2.0cm(2)). The shallow junction cell shows more resistance to 1 MeV electron radiation than the deep one. After isochronal or isothermal annealing the density and the number of deep level traps induced by irradiation are reduced effectively for the solar cells with deep junction and bombardment under high electron fluences.

Structure and device characteristics of AlxGa1-xAs/GaAs solar cells

AlGa1-xAs/GaAs heterostructures have been grown by two different liquid phase epitaxy (LPE) modes, i.e. the supercooled and melt-etch methods, for the fabrication of highly efficient solar cells. Typical structural characteristics observed under a transmission electron microscope (TEM), an Auger energy spectrometer (AES) and corresponding device parameters were presented. The results indicated that the P+PNN+ configuration grown by the melt-etch method could be used to produce high performance, large area solar cells with effectively reducing the defects of the substrate and improving the minority carrier collection by forming a compositionally graded region in the window layer.

Thermal analysis and test for single concentrator solar cells

A thermal model for concentrator solar cells based on energy conservation principles was designed. Under 400X concentration with no cooling aid, the cell temperature would get up to about 1200℃.Metal plates were used as heat sinks for cooling the system, which remarkably reduce the cell temperature. For a fixed concentration ratio, the cell temperature reduced as the heat sink area increased. In order to keep the cell at a constant temperature, the heat sink area needs to increase linearly as a function of the concentration ratio. GaInP/GaAs/Ge triple-junction solar cells were fabricated to verify the model. A cell temperature of 37℃ was measured when using a heat sink at 400X concentratration.

Characterization of polymorphous silicon thin film and solar cells

Polymorphous silicon (pm-Si:H) films have been prepared by a new regime of plasma enhanced chemical vapour deposition in the region adjacent of phase transition from amorphous to microcrystalline state. Comparing to the conventional amorphous silicon (a-Si:H), the pm-Si:H has higher photoconductivity (sigma(ph)), better stability, and a broader light spectral response range in the longer wavelength range. It can be found from Raman spectra that there is a notable improvement in the medium range order. There are a blue shift for the stretching mode of IR spectra and a red shift for the wagging mode. The shifts are attributed to the variation of the microstructure. By using pm-Si:H film as intrinsic layer, a p-i-n junction solar cell was prepared with the initial efficiency of 8.51% and a stabilized efficiency of 8.01% (AM1.5, 100mw/cm(2)) at room temperature (T-R).