Optimization of Si solar cells with full band optical absorption increased in all polarizations using plasmonic backcontact grating

We present a numerical study on the optimization of plasmonic thin-film solar cells with full band optical absorption increased in all polarization using plasmonic backcontact gratings. Particle swarm optimization (PSO) and the finite-difference time domain (FDTD) are combined to achieve the maximum absorption enhancement. Through optimization, we obtained approximately a 288% average absorption enhancement, 304% and 273% absorption enhancement for TE- and TM-polarized illumination as compared to a bare cell. The corresponding optimal design parameters of plasmonic solar cell are P = 442 nm, h₄ = 283 nm, h₅ = 191 nm and w=238$w=238$ nm. The full band absorption enhancement arises from the waveguide-plasmon-polariton, Fabry–Pérot (FP) cavity mode and multiresonant guided modes. The average absorption enhancement under an unpolarized illumination is almost immune to the incident angle ranging from −40° to 40°. If the thickness of the light absorbing layer is increased, the absorption enhancement could be reduced significantly. And the average absorption enhancement is maximum (2.88) when the thickness of Si layer is 100 nm.