Study On Carbon-based Photonic Crystal Back Reflector In Thin Film Solar Cells

In recent ten years, the problem of energy and environment has been the focus of worldattention. In order to realize the sustainable development of energy and environment, allcountries in the world regard photovoltaic power generation as priority tasks. Today, morethan90%of the photovoltaic market is dominated by silicon based solar cell. With rich rawmaterial, mature technology and stable photoelectric performance, silicon based solar cell willbe still the dominant in the future of the photovoltaic market. But owing to the high cost, thebattery price is high and it is difficult to popularize. In order to meet the needs of massproduction of the solar cells with high efficiency and low cost, the most effective way is todevelop the thin-film solar cell. But owing to serious light transmission loss caused byreduction of the cell thickness, conversion efficiency of the battery reduces. Thus effectivebackscatter design to obtain high efficiency battery is very necessary.Serious absorption problems of traditional metallic back reflector reduce the efficiencyof the back reflector, but reflection performance of the photonic crystal based on the waveoptics is good. Due to the electromagnetic wave within the scope of the energy gap can’t getthrough, the reflectivity of one dimensional photonic crystal is higher. It has no the absorptionproblem of metal reflector, also it can adjust energy gap position by changing the refractiveindex or thickness of the material.With the experimental method of optical thin film simulation software(EssentialMacleod) and RF–PECVD, we get the a-Si:H/a-C one dimensional photonic crystal and thenstudy the nature of it. Also, we test and characterize the sample samples by using uv-visspectrophotometer, scanning electron microscope (SEM), and other instruments. This paperelaborates the above and The concrete content includes:1. With optical thin film simulation software (Essential Macleod) and RF-PECVDexperimental method, we study the influence on reflection performance which is caused bythe refractive index changes because of different materials in outermost and innermost layersfor one dimensional photonic crystal with multilayer. The results show that: One dimensionalphotonic crystal often has a quarter wavelength membrane system and both sides of outermostlayers are a layer with high refractive index. The one with this kind of structure often has a high refractive index.2. With the optical thin film simulation software-Essential Macleod, we study thebroadening method of one-dimensional photonic crystal with high reflection. The method ofbroadening the high reflection zone is to combine two kinds of one dimensional photoniccrystals which have different center wavelength. These two kinds of one-dimensionalphotonic crystal are both a quarter wavelength multilayer membrane system and on both sidesof the membrane system are high refractive index dielectric film layer. Also, the multilayerfilm composing photonic crystal is odd layer. If they directly add together, high reflectionband broadens, but in the center of the high reflection band will appear a transmission peak. Ifa low index stratum medium layer with a quarter average wavelength optical thickness isadded in the two kinds of one dimensional photonic crystal with different center wavelength,the reflection curve of the combining photonic crystal is a broad flat curve. There is notransmission rate peak and no influence on band broaden of high reflection band.3. By RF_PECVD equipment, two kinds of a-Si:H/a-C one dimensional photoniccrystal(P1and P2) with different center wavelength are made and a low refractive index layeris added to the two kinds of one-dimensional photonic crystals, which makes the modulationphotonic crystal(P1+P2). Reaction gas is silane and methane. Alternately it deposits a-Si:Hand a-C film layer. By testing the reflection spectrum, We can find something as follows: thereflectance of the first one-dimensional photonic crystal P1is nearly100%in the600-900nmband; the reflectance of the second one-dimensional photonic crystal P2is above90%in the900-1300nm band; but the modulation photonic crystal realized high reflection bandbroadening which makes the reflectivity higher than70%in wide wavelength range of600-1300nm. The width of high reflection band covers the light wavelength range thatpenetrates through thin-film solar cell. So it can be used as a back reflector of thin-film solarcell to reflect the sunlight back to solar cell interior to make full use of the sunlight, which canincrease the conversion efficiency of solar cell.