Topology Optimization for Highly-efficient Light-trapping Structure in Solar Cell

1. Abstract The limitation associated with the low optical absorption remains to be the main technical barrier that constrains the efficiency of thin-film solar cells in energy conversion. Effective design of light-trapping structure is thus critical to increase light absorption in thin-film cells. However, light trapping in thin-film solar cell is a highly complex physical phenomenon governed by several competing physical processes, which imposes a number of challenges to topology optimization. This paper presents a general, yet systematic approach exploiting topology optimization for light-trapping structure designs in solar cells. With simultaneous considerations of all competing physics, we demonstrate that the proposed genetic algorithm (GA) based non-gradient topology optimization (NGTO) approach is robust for achieving highly-efficient designs of slot-waveguide based cell with both low-permittivity and high-permittivity scattering material at single wavelength or over a broad spectrum. A comparative study between the GA based approach and the SIMP based approach for light-trapping structure optimization is made to provide insights into their performances in dealing with different nanophotonic design problems that involve both mild and severe resonances. Even though efforts have been made to improve the regularization scheme of the SIMP based approach, results show that there is a fundamental challenge of using gradient-based topology optimization approach for nanophotoic problems with high nonlinearity. 2.