Perovskite solar cells are emerging photovoltaic technology with potential for low cost, high efficiency devices. Currently, flexible devices efficiencies over 15% have been achieved. Flexible devices are of significant interest for achieving very low production cost via roll-to-roll processing. However, the stability of perovskite devices remains a significant challenge. Unlike glass substrate which has negligible water vapor transmission rate (WVTR), polymeric flexible film substrates suffer from high moisture permeability. As PET and PEN flexible substrates exhibit higher water permeability then glass, transparent flexible backside encapsulation should be used to maximize light harvesting in perovskite layer while WVTR should be low enough. Wide band gap materials are transparent in the visible spectral range low temperature processable and can be a moisture barrier. For flexible substrates, approaches like atomic layer deposition (ALD) and low temperature solution processing could be used for metal oxide deposition. In this work, ALD SnO<sub>2</sub>, TiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub> and solution processed spin-on-glass was used as the barrier layer on the polymeric side of indium tin oxide (ITO) coated PEN substrates. The UV-Vis transmission spectra of the prepared substrates were investigated. Perovskite solar cells will be fabricated and stability of the devices were encapsulated with copolymer films on the top side and tested under standard ISOS-L-1 protocol and then compared to the commercial unmodified ITO/PET or ITO/PEN substrates. In addition, devices with copolymer films laminated on both sides successfully surviving more than 300 hours upon continuous AM1.5G illumination were demonstrated.
A polarization-independent metamaterial near-perfect absorber is numerically studied in the infrared range in a two-perpendicular-nanorod design. It is shown that the absorptance and the peak wavelength associated with magnetic resonance are sensitive to the nanorod length, the thickness, and the refractive index of the spacer, while only being slightly affected by the period and the distance between neighboring nanorods. This design shows two absorption peaks with absorptance values of 89% and 83% at the wavelengths of 1.24 and 1.46 μm, respectively. Furthermore, the absorptance and the peak wavelength associated with magnetic resonance show negligible dependence on the polarization angle. These properties are advantageous for applications, including thermal sensing and selective emitters in thermophotovoltaics.