The Performance Of Aluminum-based Light Management Structures For Photovoltaic Applications

The photovoltaic-based light management structures are the dielectric optical structures depositing onto the surface of photovoltaic cell.With these structures,the spectrum utilized by the underlying cell can be efficiently tailored through di-electric engineering to improve the spectrum efficiency and performances of cell,making the light management structure is a timely topic among the community.In this thesis,with highly-economical material Al,we have systematically studied the optical properties of diverse Al-based dielectric structures,including Al/dielectric stacks,spherical Al nanoparticles,hybrid Al-mixed dielectric composite,as well as Al-grating,and obtained some meaningful guidelines shown below.Firstly,we have investigated the optical properties of metal/dielectric stacks for thermophotovoltaic applications.It is observed that the unreasonable results can be derived from the calculations once the classical Drude dispersive model is used for the metal sublayer.By numerically fitting the experimentally-measured data of Al,our calculations on the Al/Al₂O₃ stack shows Al₂O₃/Al/Al₂O₃sandwich-type stack has a superior performance,which is also comparable to those of traditional all-dielectric photonic crystal structure.For the typical GaSb thermophotovoltaic cell applications,the specific structure parameters of sandwich stack should be controlled as 356⁴01（121¹54）nm for the bottom（top）Al₂O₃layer and only 4 nm or so for the Al interlayer.Secondly,we have studied the optical scattering properties of spherical Al nanoparticles.It is shown that spherical Al nanoparticle with radius r=100 nm is an effective forward scatter and has superior broadband forward scattering properties when the nanoparticle is embedded into the homogeneous Si₃N₄ and TiO₂ medium.Besides,comparing to pure metallic Al-sphere,our simulations demonstrate that the Al core-dielectric shell structure is also an effective forward scatter,implying the possible oxidation of Al metallic nanoparticles has little effect on its optical scattering properties.Thirdly,we have investigated the optical transmission properties of Al-mixed dielectric layers.It is shown that with a proper portion of Al nanoparticles the optical transmittance could be enhanced;for typical GaSb thermophotovoltaic cell,this optimum volume fraction of Al is 10%or so for the single Al:SiO₂ composite layer;while for Al₂O₃/TiO₂ dual-layer antireflection coatings is concerned,our calculations demonstrate that only 1²%Al nanoparticle embedded into the TiO₂sublayer shows visible transmittance enhancement when the radiator temperature is controlled in the range of 1000¹500 K.Finally,we have discussed the optical absorption enhancement of ultrathin Si active layer,the thickness of which is only 50 nm.Our calculations show that for the standard AM 1.5G solar spectrum,the specific structure parameters of topmost Al-grating should be controlled as the period P=450 nm,the fill factor F=0.2,and the grating height h=60 nm.With this optimum Al-grating,the photo-generated current of ultrathin Si layer has been enhanced in the ratio of 47%when comparing to that for the ultrathin Si active layer without the top Al-grating.