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Araújo, A, Mendes MJ, Mateus T, Costa J, Nunes D, Fortunato E, Águas H, Martins R.  2018.  Ultra-fast plasmonic back reflectors production for light trapping in thin Si solar cells. Solar Energy. 174:786-792. AbstractWebsite

A fast method is presented to fabricate plasmonic light trapping structures in just ten minutes (>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 (μc-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.

Brites, MJ, Barreiros MA, Corregidor V, Alves LC, V. Pinto J, Mendes MJ, Fortunato E, Martins R, Mascarenhas J.  2019.  Ultrafast Low-Temperature Crystallization of Solar Cell Graded Formamidinium-Cesium Mixed-Cation Lead Mixed-Halide Perovskites Using a Reproducible Microwave-Based Process. ACS Applied Energy Materials. 2:1844-1853., Number 3 AbstractWebsite

The control of morphology and crystallinity of solution-processed perovskite thin-films for solar cells is the key for further enhancement of the devices’ power conversion efficiency and stability. Improving crystallinity and increasing grain size of perovskite films is a proven way to boost the devices’ performance and operational robustness, nevertheless this has only been achieved with high-temperature processes. Here, we present an unprecedented low-temperature (<80 °C) and ultrafast microwave (MW) annealing process to yield uniform, compact, and crystalline FA0.83Cs0.17Pb(I(1–x)Brx)3 perovskite films with full coverage and micrometer-scale grains. We demonstrate that the nominal composition FA0.83Cs0.17PbI1.8Br1.2 perovskite films annealed at 100 W MW power present the same band gap, similar morphology, and crystallinity of conventionally annealed films, with the advantage of being produced at a lower temperature (below 80 °C vs 185 °C) and during a very short period of time (∼2.5 min versus 60 min). These results open new avenues to fabricate band gap tunable perovskite films at low temperatures, which is of utmost importance for mechanically flexible perovskite cells and monolithic perovskite based tandem cells applications.