Light Trapping In Thin-film Silicon Solar Cells For Efficiency Enhancement

Via plasma enhanced chemical vapor deposition method,thin-film Si solar cells are deposited on desired substrates with advantages of large scale,rich materials,low cost and facile process.However,the thickness of photoactive layer is only a few hundred nanometers to several micrometers;it is really insufficient to achieve a high capture of incident light.Light-trapping technologies is critical for lifting photoelectric conversion efficiency.Herein,light-trapping characteristics of metal plasma resonance,multiscale structures and spectral upconversion were investigated for efficiency enhancement in Si thin-film solar cell.Plasma resonance induces light trapping for efficiency enhancement of thin-film Si solar cell.Using ultrathin porous membranes of anodic aluminum oxide as evaporation masks,highly ordered Au nanodot arrays were deposited on glass.Size of Au nanodot was adjusted to 30-80 nm by controlling nanopore' dimension.FDTD simulation revealed that light absorption of Si layer was substantially increased when Au nanodot arrays were used as the rear light-trapping scheme.Moreover,with increasing the size of Au nanodot,the light absorption in 700-1100 nm was enhanced.Multiscale structures enhance conversion efficiency of thin-film Si solar cell.Based on micro-/nanofabrication processes,three kinds of multiscale structures were prepared,porous pit arrays,porous cone arrays and porous pyramidal structure.Via UV nanoimprint,they were transferred on glass to compare their light trapping effect.Results showed that multiscale structures enjoyed lower reflectance and higher scattering.Especially,porous cone arrays reduced the reflectance to 6.4%,and exhibited the highest haze of 82.6%in 700-1100 nm.In contrast,values were 6.g%and 56.4%of porous pit arrays,as well as 7.0%and 56.9%of porous pyramidal structure.Under AM 1.5 solar spectrum,the efficiency enhancement was 4.7%by imprinting porous cone arrays on micromorph cell,4.1%of porous pit arrays and 4.0%of porous pyramid.In addition,contact angles of multiscale structures were around 130°,demonstrating the excellent self-cleaning function.Upconversion was explored for efficiency enhancement in thin-film Si solar cell.Hydrothermal method was used to prepare the rare-earth upconversion materials,NaYF4:Yb3+/Er3+(18/2 mol%).Thermodynamically cubic-to-hexagonal(???)phase evolution was investigated by XRD and SEM analysis.The morphology of ?-NaYF4:Yb3+/Er3+(18/2 mol%)was described to prism with the hexagon cross section.Under 980 nm laser excitation,strong emission peaks at 655,543 and 525 nm were observed in photoluminescence spectra,indicating prisms could convert the sub-bandgap near-infrared light to the visible light.Prisms were dispersed into polymethylmethacrylate/chloroform solution and spin-coated on the rear of a-Si:H cell as upconversion layer.Under AM 1.5 solar spectrum through a 980 nm optical filter,the short-circuit current of cell with upconversion layer was enhanced to 0.5 mA from 0.4 mA of reference cell.Light trapping methods in this dissertation are of great significance to explore micro/nano-photonics technologies for enhancing the photoelectric conversion efficiency in thin-film Si solar cells.