Design of anodic aluminum oxide rear surface plasmonic heterostructures for light trapping in thin silicon solar cells

A metal-dielectric heterostructure that provides the combined capability of light trapping and surface passivation is reported. The light-trapping layer employs a porous aluminum anodic oxide (AAO) with metal nanoparticles formed in the pores on the rear surface of a thin crystalline silicon solar cell. Numerical finite-difference time domain (FDTD) simulations were performed to determine the pore diameter and spacing that would result in optimal light trapping for this metal-dielectric heterostructure. For a 2.5-μm-thick crystalline silicon device, the optimal pore diameter and spacing were determined to be ∼250 and ∼450 nm, respectively. These conditions resulted in an enhancement of the simulated photocurrent by ∼12.6% compared with a device in which the heterostructure was replaced with a homogenous aluminum oxide layer. Simulations also confirmed that the thickness of an underlying dielectric layer should be minimized to 10-20 nm, with the AAO barrier layer being maintained as thin as possible. Finally, it was shown that replacement of silver by aluminum in the pores resulted in a reduction in the photocurrent of 6.3% and would necessitate much larger pore spacing that is difficult to achieve experimentally and would result in thicker AAO barrier layers, which are undesirable.