Absorption Enhancement Of Poly-crystalline Silicon Thin Film Solar Cells Excited By The Silver Nanoparticles Light Trapping Structure

In recent years, polycrystalline silicon thin film solar cells have drawn an increasing concern due to its well performed electrical properties and relatively lower cost. However, the contradictory between the effective optical absorption of thin film solar cells and carrier collection, namely, the thickness design of the solar cell must guarantee the maximum effective carriers collection, induced the novel light trapping structure suitable for thin film solar cells became research hotspot.In our research, Ag nanoparticles (NPs) were prepared on glass and single crystal silicon (Si) by using the magnetron sputtering with subsequent in situ or rapid thermal annealing. We further explored the influence of parameters (annealing modes, film thickness, annealing temperature) on the morphology and optical properties of Ag NPs and preparation methods of Ag NPs for better performance have obtained. Then we prepared Ag nanoparticles on polycrystalline silicon thin film solar cell as the light trapping structures and studied the enhancement of the electrical properties of solar cells incorporated with Mie theory. The main results of the experiment are as follows:1. Metal Ag nanoparticles were prepared by magnetron sputtering with the subsequent in situ annealing (a heating rate of 0.33℃/s) process. The morphology of the particles was characterized by a scanning electron microscope (SEM). The NPs exhibit a wide range of particle size distribution, and a large number of Ag particles with size less than 50 nm are existed. The UV-visible spectrophotometer (UV-VIS) study found that with the increase of the average particle size of Ag nanoparticles, the extinction peak occurred obvious redshift and the full width at half maximum (FWHM) of the extinction spectrum can reach up to 250 nm.2. The study of Mie theory finds that the optical properties of Ag NPs with size less than 50 nm are dominated by the self-absorption. For example, when the particle size is 50nm, the absorption is higher than 50% when the wavelength range from 300 to 1100 nm and the self-absorption of the NPs can reach up to 5% when the size decreased to 20 nm. Therefore, it is vital to eliminate the Ag NPs with small size in the preparation of light trapping structure, thus improve the optical scattering properties effectively.3. Metal Ag nanoparticles were prepared by magnetron sputtering with the subsequent rapid thermal annealing (a heating rate of 150℃/s) process. Morphological analysis shows that the particle size demonstrates a gauss distribution. Rapid heating mode can effectively eliminate the small size nanoparticles and the average particle diameter increases as the film thickness increasing gradually. The maximum intensity of extinction peak can reach up to 63% and the peak position can be adjustable in the range of 418～460 nm by optimizing annealing modes.4. We prepared the ZnO buffer layer, seed layer, polycrystalline silicon solar cell active area and the Ag nanoparticle light trapping structure on graphite substrate successively. The study finds that Ag NPs can effectively improve the optical absorption properties of thin film solar cells and the short-circuit currents have a relative increase by 10.7% with respect to the solar cell without Ag NPs.