Misaligned conformal gratings enhanced light trapping in thin film silicon solar cells

Abstract

The effect of the relative lateral displacement between the front and back sinusoidal textured layers of a conformal grating solar cell on light trapping was investigated. For various amount of relative lateral displacements and thicknesses of the active layer, the external quantum efficiency (EQE) of the misaligned solar cell structures and their EQE enhancement relative to the aligned structure were studied. For both aligned and misaligned solar cell structures, the electric field distribution at the wavelength corresponding to the EQE peaks was analyzed, and the corresponding guided modes were identified. Additional modes were observed in the misaligned grating structures. A 25.1 times enhancement of the EQE at the wavelength of 950 nm and an average of 2.2 times enhancement in the wavelength range from 700 to 900 nm were observed. For the misaligned grating structure with the phase shift β = π/4 and the active layer thickness D(Si) = 230 nm, a maximum short circuit current density J(sc) enhancement of 34% was achieved for normal incidence, and a short circuit current enhancement of more than 15% was obtained for the incident angle between -15° and + 15°.

Mismatched front and back gratings for optimum light trapping in ultra-thin crystalline silicon solar cells

“…[12][13][14]17,[27][28]33 By combining a front and back grating, recent studies have demonstrated enhancement to light trapping that outperforms absorbers that are textured only on one side. [27][28][29][30][31][32][33][34][35][36][37][38][39] Further improvements for these double grating structures have included the introduction of a phase shift through misalignment of two gratings and the use of blazed gratings to break symmetry. 30,[38][39][40] To optimize the double grating structure, a general design strategy was proposed in which the front grating is treated as an anti-reflection layer to couple incident light while the back grating diffracts light into guided modes to trap it within the thin film.…”

“…[27][28][29][30][31][32][33][34][35][36][37][38][39] Further improvements for these double grating structures have included the introduction of a phase shift through misalignment of two gratings and the use of blazed gratings to break symmetry. 30,[38][39][40] To optimize the double grating structure, a general design strategy was proposed in which the front grating is treated as an anti-reflection layer to couple incident light while the back grating diffracts light into guided modes to trap it within the thin film. 28,33 The periodicities of both the front and back grating are therefore crucial to the overall performance.…”

Light Trapping Textures Designed by Electromagnetic Optimization for Subwavelength Thick Solar Cells

“…(2) To evaluate the light trapping performance of a texture for a flat-plate, non-concentrating, non-tracking solar cell, we report the absorption enhancement averaged over frequency and over all angles in the hemisphere. A valid comparison against the ray optics limit must be angle-and frequency-averaged, instead of over a limited angular range [9,10,11,20,21,22,23,24,25] or a narrowband of frequencies [26,27].…”