Effect Of Novel Micro-nano Light Trapping Structures On The Properties Of Si Thin Film Solar Cells

Si thin film solar cells have been widespread concerned because of its advantages: less material consumption,simple production process,possibility to deposition on cheap substrates like glasses,plastics,and so on.Since the typical thickness of the absorption layer in thin film solar cells is about several micrometres which is difficult to absorb incident light sufficiently.Especially for infrared light(wavelength more than 750nm),the absorption capacity is more weaker.It is one of important reasons that the efficiency of Si thin film solar cells is lower than conventional crystalline silicon solar cells.Light trapping is one of the effective means to increase the efficiency of solar cells by improving light absorption of solar cells.In recent years,the design of efficient light trapping structure in thin film solar cells has become a hot research direction.The main contents of this paper are the design and research of efficient light trapping structures in Si thin film solar cells.Three kinds of Micro-nano back reflector structures(metal Al grating,inverse opal structure 3D PC and their combination)are designed at the back of Si thin film solar cells by utilizing the MEEP software based on Finite Difference Time Domain(FDTD)method.Si thin film solar cells with traditional flat metal Al back reflector is considered as a reference cell.The light absorption of Si thin film solar cells with thickness of the absorption layer is 4μm and three kinds of back reflector structures are systematically researched.Further,the photovoltaic performances of Si thin film solar cells with three kinds of back reflector structures are researched by using the wxAMPS software.The research results show that:(1)For Si thin film solar cells with metal Al grating back reflector,when the metal Al grating with the structural parameters is P = 600 nm,H = 90 nm,and D=180nm,compared to the reference cell,the average absorption rate of this solar cells in wavelength range of 750-1200 nm and 300-1200 nm can be improved by 45.4% and 17.6%.The short-circuit current of Si thin film solar cells is increased from 17.1mA/cm2 to19.1 mA/cm2 and the photoelectric conversion efficiency is improved from 8.3% to11.9%.(2)For Si thin film solar cells with inverse opal structure 3D PC the back reflector,when the photonic crystals with the structural parameters of air medium sphere is R=150nm and L=2.Compared to the reference cell,the average absorption rate of this solar cells in wavelength range of 750-1200 nm and 300-1200 nm can be improved a relative amount of 34.8% and 30.5%.The short-circuit current of solar cells is increased from 17.1mA/cm2 to 20.7mA/cm2 and the photoelectric conversion efficiency is improved from 8.3% to 13.0%.(3)For Si thin film solar cells with combined structure back reflector,Compared to the reference cell,this soalr cells has the best light absorption in wavelength range of 300-1200 nm.The average absorption rate can be improved a relative amount of 32% which is better than metal grating or photonic crystals.The short-circuit current of solar cells is increased from 17.1mA/cm2 to 21.6mA/cm2 and the photoelectric conversion efficiency is improved from 8.3% to 13.5%.In conclusion,compared to traditional flat metal Al back reflector,metal Al grating back reflector structure can mainly enhance the absorption of Si thin film solar cells in infrared light erea.3D PC back reflector structure can improve the absorption of Si thin film solar cells in entire spectrum obviously.The combination back reflector structure can bring the optical absorption for Si thin film solar cells in entire spectrum which is better than metal grating or 3D PC.Due to the optical properties of grating and photonic crystals(diffraction and scattering effect in grating and bandgap structure in photonic crystals,and so on),light through the absorption layer can be reflected back into solar cells with a higher reflectance which makes it could be absorbed two or more times.So the light absorption of Si thin flim solar cells can be improved.Thus,three kinds of light trapping back reflector structures can bring different degrees of photovoltaic performance improvement for silicon thin film solar cells.