Plasma-enhanced chemical vapor deposition (PECVD) SiN films are widely used as antireflection (AR) coating for silicon solar cells and particularly for multi-crystalline solar cells for hydrogen passivation of bulk defects. In this paper, the detailed optical properties of various SiN films and their effect on silicon solar cell efficiency in air and under glass is evaluated by a combination of Monte-Carlo geometrical ray tracing program, Sunrays, and a device modeling program PC1D. Maximum module power under glass and ethylene vinyl acetate (EVA) encapsulation is used as the figure of merit for optimizing the index and thickness of the SiN films. Simulations are categorized by surface morphology (planar or textured) and ambient (air or glass). SiN films with refractive index (n) in the range of 2.03-2.42 are used for this study. It is found that although n ¼ 2.03 is not the optimum index in terms of reflectance under glass (n ¼ 1.5), it produces maximum cell or module efficiency under glass. This is because n ¼ 2.03 film produces much higher cell efficiency (17.9%) in air, therefore, even after a significant optical encapsulation loss of 0.8% in absolute efficiency, the cell efficiency remains highest (17.1%) under glass. In contrast SiN film with an index of 2.4 produces only 0.5% air to glass efficiency loss but due to the low starting efficiency of 17% in air; the final cell efficiency under glass is only 16.5%. In addition, texturing provides a larger window of thickness around the optimum without affecting the optical performance. Similar analysis done for planar cells indicate that optimum index for highest module power is 2.20. This is because reflection is much higher in planar cells, therefore higher index can be tolerated before loss due to absorption in SiN exceeds the gain in reflectance under glass.
We investigated a promising, low-cost method for fabrication of semitransparent organic solar cells by mass production. The active layer of the organic solar cells was added by spray coating with a dual action airbrush. The solution for the active layer was prepared from a rigorously blended poly(3-hexylthiophene-2,5-diyl) (P3HT) and (6,6)-Phenyl-C61 butyric acid methyl ester (PCBM) in 1,2-dichlorobenzene, and the surface morphology of the spray-coated active layer depending on the concentration of the P3HT and PCBM was investigated. The semitransparency achieved, came from the use of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as the conductive polymer electrode. For comparison, spin-coated solar cells were also fabricated. Power-conversion efficiency and transparency was achieved from the lower cost spray-coating method that was comparable to those by the traditional spin-coating method. The best spray-coated solar cell exhibited power-conversion efficiency of 1.9% (average or 1.7%) while the best spin-coated solar cell was 2.0% (average of 1.6%), when both were measured under the AM1.5G spectrum 100 mW/cm 2 light. Transmittance of the spray-coated solar cell was 52.2% while that of the spin-coated solar cell was 51.2%.INDEX TERMS Spray-coating, organic solar cell, semitransparent, inverted, conductive polymer.
This paper shows for the first time a comparison of commercial-ready n-type passivated emitter , rear totally diffused solar cells with boron (B) emitters formed by spin-on coating, screen printing, ion implantation, and atmospheric pressure chemical vapor deposition. All the B emitter technologies show nearly same efficiency of~20%. The optimum front grid design (5 busbars and 100 gridlines), calculated by an analytical modeling, raised the baseline cell efficiency up to 20.5% because of reduced series resistance. Along with the five busbars, rear point contacts formed by laser ablation of dielectric and physical vapor deposition Al metallization resulted in another 0.4% improvement in efficiency. As a result, 20.9% efficient ntype passivated emitter, rear totally diffused cell was achieved in this paper.
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