Abstract
The article presents a nanoparticle-based buried light-scattering (BLiS) back-reflector design realized through a simplified nanofabrication technique for the purpose of light-management in solar cells. The BLiS structure consists of a flat silver back-reflector with an overlying light-scattering bilayer which is made of a TiO2 dielectric nanoparticles layer with micron-sized inverted pyramidal cavities, buried under a flat-topped silicon nanoparticles layer. The optical properties of this BLiS back-reflector show high broadband and wide angular distribution of diffuse light-scattering. The efficient light-scattering by the buried inverted pyramid back-reflector is shown to effectively improve the short-circuit-current density and efficiency of the overlying n-i-p amorphous silicon solar cells up to 14% and 17.5%, respectively, compared to the reference flat solar cells. A layer of TiO2 nanoparticles with exposed inverted pyramid microstructures shows equivalent light scattering but poor fill factors in the solar cells, indicating that the overlying smooth growth interface in the BLiS back-reflector helps to maintain a good fill factor. The study demonstrates the advantage of spatial separation of the light-trapping and the semiconductor growth layers in the photovoltaic back-reflector without sacrificing the optical benefit.
Highlights
The advantages of silicon thin-film solar cells such as the low consumption of raw material and the possibility of large-area fabrication, are counterbalanced by the reduced absorption of incident light in the thin absorber layer [1,2]
The efficient light-scattering by the buried inverted pyramid back-reflector is shown to effectively improve the short-circuit-current density and efficiency of the overlying n-ip amorphous silicon solar cells up to 14% and 17.5%, respectively, compared to the reference flat solar cells
We have previously demonstrated a light-trapping nano-crater back-reflector fabricated by molding of TiO2 nanoparticles (TiO2-NP) [30], and recently we presented, a buried light-scattering (BLiS) back-reflector using TiO2NPs molded into pyramidal microstructures buried within a flat top layer of silicon nanoparticles (Si-NP) [23]
Summary
The advantages of silicon thin-film solar cells such as the low consumption of raw material and the possibility of large-area fabrication, are counterbalanced by the reduced absorption of incident light in the thin absorber layer [1,2]. Among various kinds of structures explored for their light-trapping performance, upright pyramidal and inverted pyramidal nano- and microstructures are extensively studied in crystalline silicon solar cells [9,10,11], but less so in the context of silicon thin-film solar cells [12,13]. Applying theoretically promising optical designs of back-reflectors in solar cell devices throws up the challenge of extensive optimization of growth conditions to reconcile solar cell quality with substrate roughness. This feasibility problem, while possibly surmountable in the laboratory setting, may prove to be prohibitive for scaling up the design to industrial manufacturing.
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