Deterioration Of Fill Factor Research Articles

Application of Large Area TiO2 Photoelectrode on Dye-Sensitized Solar Cells

The scale-up of dye-sensitized solar cell (DSSC) has been a big issue as the DSSC technology process progresses from laboratory scale to large area applications. Meanwhile, this type of solar cell has been of great interest among PV scientist and academics as it can be produced in lower-cost processes compared to the conventional solar cells which are mostly fabricated from silicon. The fabrication of DSSC prototypes with a relatively large active area of 9x9 cm2 are demonstrated in this paper. Large area of TiO2 surface has been shown to significantly increase the ISC, as well as VOC and Pmax. Nevertheless, deterioration of fill factor (FF) was observed as the result of the increase on series resistance with respect to the increase in the photoelectrode area.

Improvement of Screen-Printed Textured Monocrystalline Silicon Solar Cell Performance by Metal-Assisted Chemical Etching

In this work, we investigate the potential use of stain etched porous silicon as one possible way to increase the silicon solar cell efficiency at low cost. A very simple method for the formation of porous silicon antireflection coatings on random pyramid textured screen-printed monocrystalline silicon solar cells is described. The process is based on electroless metal-assisted chemical etching by immersion of the fully processed cell in HF-H2O2-Ethanol without masking the contacts. Characterization of the porous silicon layer using SEM, EDX and UV-VIS-NIR spectrophotometry revealed that silver nanoparticles that are dissolved from the unmasked front grid contact by the HF acid greatly enhance the dissolution rate and therefore serve as catalysts for the porous silicon etching. The solar cell weighted reflectance was reduced from 45.08% to 22.01% after texturization and dropped further to 11.34% after porous silicon formation under optimized conditions. The porous silicon antireflection layer led to a relative improvement of 24.64% in the short-circuit current density without fill factor deterioration. The open-circuit voltage increased by ∼7mV and the cell efficiency was raised by 2.3% absolute. The simplicity of the process makes it attractive for the cost-effective production of silicon solar cells.

Interface modification effect between p-type a-SiC:H and ZnO:Al in p-i-n amorphous silicon solar cells

Aluminum-doped zinc oxide (ZnO:Al) [AZO] is a good candidate to be used as a transparent conducting oxide [TCO]. For solar cells having a hydrogenated amorphous silicon carbide [a-SiC:H] or hydrogenated amorphous silicon [a-Si:H] window layer, the use of the AZO as TCO results in a deterioration of fill factor [FF], so fluorine-doped tin oxide (Sn02:F) [FTO] is usually preferred as a TCO. In this study, interface engineering is carried out at the AZO and p-type a-SiC:H interface to obtain a better solar cell performance without loss in the FF. The abrupt potential barrier at the interface of AZO and p-type a-SiC:H is made gradual by inserting a buffer layer. A few-nanometer-thick nanocrystalline silicon buffer layer between the AZO and a-SiC:H enhances the FF from 67% to 73% and the efficiency from 7.30% to 8.18%. Further improvements in the solar cell performance are expected through optimization of cell structures and doping levels.

High efficiency amorphous and nanocrystalline silicon based multi-junction solar cells deposited at high rates on textured Ag/ZnO back reflectors

AbstractWe report our recent progress on nc-Si:H single-junction and a-Si:H/nc-Si:H/nc-Si:H triple-junction cells made by a modified very-high-frequency (MVHF) technique at deposition rates of 10-15 Å/s. First, we studied the effect of substrate texture on the nc-Si:H single-junction solar cell performance. We found that nc-Si:H single-junction cells made on bare stainless steel (SS) have a good fill factor (FF) of ˜0.73, while it decreased to ˜0.65 when the cells were deposited on textured Ag/ZnO back reflectors. The open-circuit voltage (Voc) also decreased. We used dark current-voltage (J-V), Raman, and X-ray diffraction (XRD) measurements to characterize the material properties. The dark J-V measurement showed that the reverse saturated current was increased by a factor of ˜30 when a textured Ag/ZnO back reflector was used. Raman results revealed that the nc-Si:H intrinsic layers in the two solar cells have similar crystallinity. However, they showed a different crystallographic orientation as indicated in XRD patterns. The material grown on Ag/ZnO has more random orientation than that on SS. These experimental results suggested that the deterioration of FF in nc-Si:H solar cells on textured Ag/ZnO was caused by poor nc-Si:H quality. Based on this study, we have improved our Ag/ZnO back reflector and the quality of nc-Si:H component cells and achieved an initial and stable active-area efficiencies of 13.4% and 12.1%, respectively, in an a-Si:H/nc-Si:H/nc-Si:H triple-junction cell.

On the sensitivity of open-circuit voltage and fill factor on dangling bond density and Fermi level position in amorphous silicon p–i–n solar cell

Abstract A simple method for calculation of current–voltage characteristics of an amorphous silicon solar cell is described in terms of excitation current, J G , and excitation voltage, V G , the latter being defined in terms of separation of quasi-Fermi levels. Contrary to the usual method of calculating the short-circuit current and dark current separately and assuming a linear superposition, in the present method the calculations are done first in the open circuit where the neutrality of space charge can be assumed and then the current has been calculated in terms of a gradient in the quasi-Fermi levels. We find that depending on other parameters, the open-circuit voltage is a weak function of dangling bond density except in cases of very large degradation. The sensitivity of open-circuit voltage, V oc , to light-induced degradation can further be reduced by moving the thermal equilibrium Fermi level above the upper dangling bond level. Fill factor deterioration is found to be mainly due to conductivity modulation and is higher for the lower values of thermal equilibrium Fermi level.