Design And Fabricate Multi-scale Light Trapping Structure

Crystalline silicon solar cells dominate the PV market for its advantages of high efficiency and non-toxic. To reduce the material cost, the thickness of silicon absorption layer is reduced continuously. However, the absorption efficiency decrease with the reduction of thickness, resulting in low conversion efficiency. Light trapping structures are regards as a necessity in thin film silicon solar cells to enhance the absorption efficiency.In this paper, we analyzed the shortcomings of existing light trapping structures. We proposed novel multi-scale light trapping structures which avoids the disadvantages of existing structures. Then we designed and optimized the structures and finally make a preliminary experimental study of fabricating the structures. The main contents are as follows:First, we optimized one-dimensional multi-scale light trapping structures. Compared to single periodic structures, the short circuit current density of the solar cells with multi-scale structure is improved by 62%. Compared to random light trapping structures, the short circuit current density is improved by 28%. The optimized multi-scale structure can absorb incident lights in wide angles. When the incident angle is within the range of-60°to 60°, the solar cell absorptions change less than 15%.Then, a program was built for designing and optimizing multiscale light trapping structures, which can construct complex structure profiles that most of the commercial optical software can’t do. An optimization algorithm was integrated in the software to automatically identify a surface texture which exhibits good light trapping ability by combing global and local searching paths. Moreover, a simple user interface was in-built in this program for users to operate this software.Furthermore, on the basis of the optimized one-dimensional structure, we construct two-dimensional multiscale structures and optimized it. In contrast to the one-dimensional structures, the short-circuit current density of the solar cells with two-dimensional structure is improved by 14.7%, almost approaching the theoretical limit. In the 300nm-800 nm wavelength, the absorption is larger than 0.75 when the incident angle is within the range of-60°to 60°.Finally, we made a preliminary study of fabricating the multi-scale structures by interference lithography. We firstly optimized the processing parameters, and then fabricated single, dual, three and four period light trapping structures. These experimental results pave the way to accurately fabricate the target structures.