An investigation of three-dimensional texturing in silicon solar cells for enhanced optical absorption

Application of randomly created sub-wavelength structures using either wet- or dry chemical mechanisms in Si must serve two purposes, i.e., reduces reflection and enhance near IR absorption. This absorption enhancement can only occur through diffractive scattering from random surfaces with feature dimensions of ≫ λ/n, where n is Si refractive index. For surface features with sizes ≪ λ/n, no internal diffraction is possible with textured surface behaving like a gradient index film. Absorption enhancement of ∼ 4n² between two parallel sheets has been predicted using statistical analysis. By creating three-dimensional surfaces with subwavelength textures on front and sidewalls, it may be possible to enhance absorption beyond the 4n² statistical limit. We have investigated SILVACO software to carry out a detailed simulation of three-dimensional structured surfaces integrated into conventional solar cell configuration of front and back contacts in p-type substrate using POCl3 diffusion with Al BSF. Simulations have exhibited short-circuit enhancements of ∼ 4 mA/cm² for two-dimensional and ∼ 8 mA/cm² for three-dimensional textured surfaces. Solar cells fabricated using p-type substrates with have exhibited short-circuit gain of ∼ 7.5 mA/cm² for textured surface over a planar surface. Ever superior performance will be achievable following SiN anti-reflection and surface passivation combined with emitter and contact optimization.