Ag~+ Ion Exchanged Glasses For Spectral Down-converting Of Sunlight

Fossil energy shortage and pollution problem restrict the sustainable development of human beings.Solar energy is an abundant and clean energy that can be captured by solar cells and transformed into electricity.The efficiency of current commercial solar cells is low,how to improve the efficiency of solar cells is the research focus of many scholars.Modifying the solar spectrum by down-shifting materials can improve the efficiency of solar cells to UV-light.In this paper,we introduced silver into the surface layer of aluminosilicate glasses by Silver ion-exchanged.The original glasses were immersed in the molten salt bath of AgNO₃ and KNO₃ with molar ratios of 0.1%,0.3%,0.5%,and 1.1%（glasses exchanged in these salts were named as AG01,AG03,AG05 and AG11,respectively）at 350。C for 1 h.Distributions of Ag in the exchanged layer of glasses were analyzed using electron probe micro-analysis.Effects of salt composition and annealing conditions on the distribution,valence and clustering states of silver were investigated through emission and excitation spectra measurement.Using the silver ion-exchanged glass as cover,the I-V curves and quantum efficiency ofα-Si solar cell were tested.The experimental results are as follows:（1）After ion-exchanging,The Ag⁺ions gathered in the range about 30μm from the glass surface.The depth profile of silver was strongly dependent on the annealing time.Upon thermal annealing at 410。C or 440。C for 1 h and 10 h,concentration of silver in the surface layer respectively diffused into around 75μm and 200μm.（2）The introduction of the Ag⁺ions made the absorption edge of samples shifted towards to longer wavelength,and the red-shift of the absorption edges of the as-exchanged glasses was strongly dependent on the concentration of AgNO₃.Upon thermal annealing,absorption edges of the thermally annealed glasses showed some blue-shift,and the absorption shoulders appeared at 310 nm to 400nm,which became more obvious with higher annealing temperature and longer annealing time.（3）Upon UV excitation（250-400 nm）,silver ion-exchanged glasses showed three distinct bands centers at 420 nm,480 nm and 530 nm,exhibiting great potential for the UV light down-shifting.Both isolated Ag⁺ions and mixed species of Ag⁺ ions and Ag⁰ atoms can yield emission at 420 nm band when excited at 285 nm and 355 nm.The mixed species of Ag⁺ions and Ag⁰ atoms mainly contribute to the emission at 480 nm.For the 530 nm band emission,the mixed species of Ag⁺ ions and Ag⁰ atoms,and Ag₂²⁺clusters were mainly responsible upon exciation at 355 nm and 395 nm.Properly increasing the annealing temperature and time can promote the formation of mixed species of Ag⁺ions and Ag⁰ atoms.（4）Covered AG01 sample upon thermal annealing at 410。C for 10 h,the highest output power ofα-Si solar cell could be improved slightly comparing with the original glass.Covered AG03,AG05 and AG11 samples upon thermal annealing at 410。C for 1 h,the highest output power ofα-Si solar cell could be improved comparing with the as-exchanged glass.Using these silver ion-exchanged glasses as covers,quantum efficiency ofα-Si solar cell before 318 nm spectra range was improved.