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

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°.