Study On The Light Trapping Properties Of Thin Film Solar Cells Based On Silver Micro And Nano Structure

Thin film solar cells, with absorber layer thicknesses ranging from a few hundred nanometers to a few microns, combine the advantages of relatively low fabrication cost and a low degree of carrier recombination. However, the small absorber layer thickness leads to poor absorption at energies close to the electronic bandgap of the semiconductor.Light trapping schemes are thus needed to enhance light absorption. Metallic nanostructures supporting surface plasmons have been proposed as a method to achieve light trapping in thin-film solar cell. The surface plasmon effect of metal micro and nano structures has the property of the near-field enhancement. These subwavelength nanostructures strongly interact with the incident light and couple light into thin semiconductor layers, thereby they could enhance the light absorption. Based on the background mentioned above, this paper focused on calculations and a systematic study of the impact of metal micro and nano structures on light trapping efficiency of the solar cells,by introducing Comsol Multiphysics, a software based on the principle of finite element.Firstly, the spherical silver nano arrays were designed at different positions of the silicon substrate by using the simulation software Comsol Multiphysics. The reflection,transmission, absorption and photoelectric conversion efficiency were calculated and compared with the bulk silicon of the same thickness. It was found that when the silver nano arrays were located at the top of the substrate, the reflection of the solar cells obviously decreased and the transmittance(absorption and transmission) significantly increased. Thus the light trapping effect was improved.Secondly, the effect of the particles radius and array period on light trapping efficiency of the solar cells was investigated, when the spherical silver nano arrays were designed at the top of the substrate. It was found that when the radius of the particles was larger than 80 nm and the arrays period was 4-6 times of the radius, the light trapping effect was better.Thirdly, the impact of the metal back reflectors on light trapping efficiency of the solar cells was researched. It is found that when a 70 nm thick flat metal back reflectorwas designed at the bottom of the substrate, the transmission of the solar cells reduced to 0,accordingly the absorption and photoelectric conversion efficiency all improved, but the reflection also increased. When a patterned metal reflector was designed at the bottom of the solar cells, the reflection of the solar cells reduced, as expected, the absorption and photoelectric conversion efficiency further improved.Finally, the impact of the particles height at the top of the substrate on light trapping efficiency was studied, when a patterned metal reflector was designed at the bottom of the solar cells. It is found that when the shape of nanoparticles closed to oblated spherical, the absorption was higher, and the light trapping effect was the best.