Toward ultimate nanophotonic light trapping using pattern-designed quasi-guided mode excitations

In this work, a shape-optimized periodic pattern design is employed to boost the short circuit current of solar cells. A decent result of an additional 16.1% enhancement in short circuit current is achieved by solely patternwise optimization, compared to the baseline structure that is already under full parameter optimization. The underlying physics is that the shape-optimized pattern leads to optimal quasi-guided mode excitations. As a result of the pattern design, a single strongly confined quasi-guided mode is replaced with several weakly confined modes, to cover a broader spectral range. Previous works of optimized periodic gratings result in gradually varied grating heights and require grayscale lithography leading to high process complexity. Using randomized pattern for isotropic Lambertian light trapping, on the other hand, leads to an overly large simulation domain. The proposed pattern design methodology achieves the optimal balance between the slow-light enhancement strength and the enhancement spectral range for nanophotonic light trapping using quasi-guided modes.