Colloidal self-assembled nanosphere arrays for plasmon-enhanced light trapping in thin film silicon solar cells

To realize high-efficiency thin-film silicon solar cells it is crucial to develop light-trapping methods that can increase absorption of the near- bandgap light in the silicon material. That can be achieved using the far-field scattering properties of metal nanoparticles (MNP) sustaining surface plasmons. The MNPs should be inserted in the back of the cell, embedded in the transparent conductive oxide (TCO) layer which separates the rear mirror from the silicon layers. In this way, a plasmonic back reflector (PBR) is constructed that can redirect light at angles away from the incidence direction and thereby increase its path length in the cell material. In this work, a novel technique is presented to fabricate PBRs (composed of Ag mirror/TCO/MNPs/TCO) containing colloidal gold MNPs patterned with a self-assembly wet-coating method. The method allows the construction of long-range ordered arrays of MNPs with monodisperse size and shape using fast, scalable, low-cost and low-temperature (<120°C) procedures. Colloidal MNPs are synthesized with spherical shapes, so their scattering properties are analytically modeled with Mie theory. Such formalism allowed the computation of the preferential MNP sizes that provide the best scattering performance for light-trapping in amorphous and microcrystalline thin-film silicon solar cells. © 2014 The Authors.