a-SiGe Solar Cells Research Articles

Fabrication of amorphous silicon–germanium thin film solar cell toward broadening long wavelength response

The morphous silicon germanium (a-SiGe) thin films are fabricated in a radio frequency plasma enhanced chemical vapor deposition system. This paper summarizes our recent works on how to make a suitable a-SiGe solar cell to enhance the light absorption in the long wavelength region. Up to now, a single junction p-i-n a-SiGe solar cell with an initial efficiency of 9.06% is obtained. The long wavelength response in QE is broadened to 950 nm. The QE reaches about 26.63% at 800 nm wavelength.

The investigation of ZnO:Al2O3/metal composite back reflectors in amorphous silicon germanium thin film solar cells

Different aluminum-doped ZnO (AZO)/metal composite thin films, including AZO/Ag/Al, AZO/Ag/nickel—chromium alloy (NiCr), and AZO/Ag/NiCr/Al, are utilized as the back reflectors of p—i—n amorphous silicon germanium thin film solar cells. NiCr is used as diffusion barrier layer between Ag and Al to prevent mutual diffusion, which increases the short circuit current density of solar cell. NiCr and NiCr/Al layers are used as protective layers of Ag layer against oxidation and sulfurization, the higher efficiency of solar cell is achieved. The experimental results show that the performance of a-SiGe solar cell with AZO/Ag/NiCr/Al back reflector is best. The initial conversion efficiency is achieved to be 8.05%.

Modeling of Tandem Solar Cell a-Si/a-SiGe using AMPS-1D Program

Modeling of thin-film silicon solar cell requires taking, the electronic structure and opto-electronic properties of the different amorphous layers into account. However, one of the programs which are convivial for this application is AMPS-1D.In this work, We have performed a Computer modeling of a-Si:H/a-SiGe:H tandem solar cells with p-i-n/p-i-n configuration using AMPS 1D.Initially, we have investigated the influence of the window layer thickness doped p in the efficiency of the amorphous silicon solar cell used as a top cell; however we have analyzed this effect more particularly in the density of currents and quantum efficiency. Also, we have proved the interest of the choice of a-SiC as window layer instead of a-Si material. Secondly, we have modeled a-SiGe solar cell used as bottom cell in tandem configuration, we have also investigated the problem of the interface between materials constituting the solar cell, especially the interface a-SiC/a-SiGe.By a suitable choice of the tunnel junction, we have successfully modelled the Tandem a-Si/a-SiGe solar cell, and the simulation results demonstrate the performances boost of the cell comparing to single junction. The results obtained from simulation give a good agreement with experimental results.

Amorphous silicon and silicon germanium materials for high-efficiency triple-junction solar cells

In this paper, we report our recent progress in the amorphous silicon (a-Si)-based photovoltaic research program at The University of Toledo (UT). We have achieved the fabrication of (1) wide bandgap a-Si solar cells with an open-circuit voltage of 0.981 and a fill factor of 0.728 using high hydrogen dilution for the i-layer deposition, (2) mid bandgap a-SiGe solar cells having an open-circuit voltage of 0.815 and a fill factor of 0.65, (3) narrow bandgap a-SiGe solar cells with 9.17% initial efficiency, and (4) triple-junction, spectrum-splitting a-Si/a-SiGe/a-SiGe solar cells with 10.6% initial efficiency.

Buffer Layers for Narrow Bandgap A-SIGE Solar Cells

AbstractIn high efficiency narrow bandgap (NBG) a-SiGe solar cells, thin buffer layers of unalloyed hydrogenated amorphous silicon (a-Si) are usually used at the interfaces between the a-SiGe intrinsic layer and the doped layers. We investigated the effect of inserting additional a-SiGe interface layers between these a-Si buffer layers and the a-SiGe absorber layer. We found that such additional interface layers increase solar cell VOC and FF sizably, most likely due to the reduction or elimination of the abrupt bandgap discontinuity between the a-SiGe absorber layer and the a-Si buffer layers. With these improved narrow bandgap solar cells incorporated into the fabrication of triple-junction a-Si based solar cells, we obtained triple cells with initial efficiency of 10.6%.

Origin of the optical gap dependence of a-SiGe solar cell stability

The effect of the optical gap (Eopt) on the thermal recovery behaviors of a-SiGe solar cells was systematically investigated. It was found that the time constant and the activation energy required for the thermal annealing of metastable defects do not strongly depend on Eopt. The independence of the activation energy from Eopt suggests that the variation of Eopt causes little energy difference in the trap depth of hydrogen, which should diffuse to remove metastable defects during network relaxation by annealing. It was also shown that the degradation ratio for narrower Eopt cells exhibits greater temperature dependence after prolonged light soaking. This tendency was analytically attributed to the Eopt dependence of the light-induced defect creation process and the Eopt independence of the thermally induced annealing process.

Effect of the optical gap on the temperature dependence of a-SiGe solar cell stability

The effect of the optical gap ( E opt) on the thermal recovery behavior of a-SiGe solar cells and on the temperature dependence of the cell stability was systematically investigated. It was found that the time constant and activation energy of thermal recovery do not depend on E opt. The independence of the activation energy from E opt suggests that the variation of E opt causes little energetic difference in the trap depth for hydrogen moving to remove defects during annealing. The steady-state defect density of the narrower E opt alloy is also considered to exhibit a greater temperature dependence than that of the wider E opt alloy, because of the E opt dependence of the light-induced creation of defects and the independence of thermal-induced annealing.

Development of high-efficiency a-Si solar cell submodule with a size of 30 cm × 40 cm

We have achieved a stabilized conversion efficiency of 8.9% in a single-junction a-Si solar cell and 10.6% in a double-junction a-Si a-SiGe solar cell for a size of 1 cm 2, which are the world's highest values achieved so far for this size and structure. We have been investigating the improvement of stability in a-SiGe film with regard to the bottom cell i-layer, and the control of E opt in a-SiGe film in order to confirm the tandem cell design. On the other hand, uniformity of ± 1% has been obtained in conversion efficiency for many small cells fabricated in a size of 30 cm × 40 cm, evaluated by using a-Si single-junction structure. As a result, we have achieved the stabilized high-effective area conversion efficiency of 8.64% in a 30 cm × 40 cm a-Si/a-Si tandem submodule. The combination of the above techniques and further optimization can be expected to achieve a stabilized conversion efficiency of more than 10% for a 30 cm × 40 cm double-junction a-Si a-SiGe submodule.

Effect of the i-Layer Optical Gap on the Light-Induced Degradation of a-SiGe Solar Cells

The light-induced degradation and thermal recovery behaviors of a-SiGe single-junction solar cells with i-layers having various optical gaps (E opt) have been investigated. The cells with narrower E opt show slower degradation under light-soaking than the cells with wider E opt. However, they recover upon thermal annealing at 150° C as fast as the cells with wider E opt. The results indicate that the light-induced processes are suppressed in the materials with narrower E opt, but that the thermally induced process does not depend on E opt. The slower light-induced processes of the cells with narrower E opt are attributable to the lower recombination energy, which is a driving force of light-induced defect creation. Differences in the hydrogen content, the hydrogen bonding configuration and the germanium content are less likely to cause variation in the degradation time constant.

Effect of optical gap on the stability of a-SiGe solar cells

The light-induced degradation and thermal recovery behaviors of a-SiGe single-junction solar cells with i-layers having various optical gaps ( E opt) have been investigated. The narrower E opt cells show slower degradation under light-soaking than the wider E opt cells. However, they recover by thermal annealing at 150°C as fast as the wider E opt cells. The results indicate that the light-induced defect creation processes are suppressed in the narrower E opt materials, but the thermally induced process does not depend on E opt. From a comparison among several samples, the E opt dependence of the light-induced processes is attributable to the difference of E opt itself, i.e., the band-to-band recombination energy, rather than to the difference of the compositions.