Physics Letters B, 795 (2019) 682–688. 10.1016/j.physletb.2019.06.069

A fast method is presented to fabricate plasmonic light trapping structures in just ten minutes ({\textgreater}5 × faster than the present state of art), with excellent light scattering properties. The structures are composed of silver nanoparticles (Ag NPs) deposited by thermal evaporation and self-assembled using a rapid thermal annealing (RTA) system. The effect of the RTA heating rate on the NPs production reveals to be crucial to the decrease of the annealing process. The Ag NPs are integrated in thin film silicon solar cells to form a plasmonic back reflector (PBR) that causes a diffused light reflectivity in the near-infrared (600–1100 nm wavelength region). In this configuration the thicknesses of the AZO spacer/passivating layers between NPs and rear mirror, and between NPs and silicon layer, play critical roles in the near-field coupling of the reflected light towards the solar cell absorber, which is investigated in this work. The best spacer thicknesses were found to be 100 and 60 nm, respectively, for Ag NPs with preferential sizes of about 200 nm. The microcrystalline silicon ($μ$c-Si:H) solar cells deposited on such improved PBR demonstrate an overall 11{%} improvement on device efficiency, corresponding to a photocurrent of 24.4 mA/cm2 and an efficiency of 6.78{%}, against 21.79 mA/cm2 and 6.12{%}, respectively, obtained on flat structures without NPs.

{\textless}h2{\textgreater}Summary{\textless}/h2{\textgreater}{\textless}p{\textgreater}Recent trends in photovoltaics demand ever-thin solar cells to allow deployment in consumer-oriented products requiring low-cost and mechanically flexible devices. For this, nanophotonic elements in the wave-optics regime are highly promising, as they capture and trap light in the cells' absorber, enabling its thickness reduction while improving its efficiency. Here, novel wavelength-sized photonic structures were computationally optimized toward maximum broadband light absorption. Thin-film silicon cells were the test bed to determine the best performing parameters and study their optical effects. Pronounced photocurrent enhancements, up to 37{%}, 27{%}, and 48{%}, respectively, in ultra-thin (100- and 300-nm-thick) amorphous, and thin (1.5-$μ$m) crystalline silicon cells are demonstrated with honeycomb arrays of semi-spheroidal dome or void-like elements patterned on the cells' front. Also importantly, key advantages in the electrical performance are anticipated, since the photonic nano/micro-nanostructures do not increase the cell roughness, therefore not contributing to recombination, which is a crucial drawback in state-of-the-art light-trapping approaches.{\textless}/p{\textgreater}

Phys. Rev. A 97, 032517 (2018). doi:10.1103/PhysRevA.97.032517

{\textless}p{\textgreater}Opto-electronics on/with paper is fostering a novel generation of flexible and recyclable devices for sunlight harvesting and intelligent optical sensing.{\textless}/p{\textgreater}

The copper zinc tin sulfide (CZTS) compound is a promising candidate as an alternative absorber material for thin-film solar cells. In this study, we investigate the direct formation of Cu1.92ZnSnx(Sb1-x)S4 compounds [CZT(A)S], with x=1, 0.85, 0.70, and 0.50, via a mechanochemical synthesis (MCS) approach, starting from powders of the corresponding metals, zinc sulfide, and sulfur. The thermal stability of the CZT(A)S compounds was evaluated in detail by in situ synchrotron high-energy x-ray diffraction measurements up to 700 °C. The CZT(A)S compounds prepared via MCS revealed a sphalerite-type crystal structure with strong structural stability over the studied temperature range. The contribution of the MCS to the formation of such a structure at room temperature is analyzed in detail. Additionally, this study provides insights into the MCS of CZTS-based compounds: the possibility of a large-scale substitution of Sn by Sb and the production of single phase CZT(A)S with a Cu-poor/Zn-poor composition. A slight increase in the band gap from 1.45 to 1.49-1.51 eV was observed with the incorporation of Sb, indicating that these novel compounds can be further explored for thin-film solar cells.

In this work, we highlight the influence of three different sol stabilizers, namely diethanolamine (DEA), Ammonium Hydroxide (NH4OH), and Nitric Acid (HNO3), on the optical and structural properties of spin-coated zinc oxide (ZnO) thin films. The XRD patterns related to all films exhibit a hexagonal crystal structure with a preferential orientation along the (0 0 2) direction. However an additional {\textless}100{\textgreater} peak arises when the films are prepared with DEA and NH4OH showing a better crystallinity than that displayed by HNO3-prepared films. The elaborated films show a high transparency reaching 80{%} for DEA-prepared films. The analysis of the transmittance and the reflectance measurements confirms a direct band-to-band transition. Depending on the sol stabilizer, the optical band gap energy is varying from 3.16 to 3.22 eV. The relatively wide band-gap of DEA-prepared ZnO films is correlated to their high crystallinity. Room temperature photoluminescence spectra indicate strong UV emission at around 377 nm originated from nearby band-edge transitions. Yet, the use of DEA as a stabilizer leads to a net intensity increase of the blue peak emission.