Polarization-insensitive Light Absorption Research Articles

Highly flexible and stable perovskite/microbead hybrid photodetectors with improved interfacial light trapping

Organic-inorganic halide perovskites are considered as a core material in optoelectronics. Particularly, perovskite-based photodetectors are promising devices for sensing and imaging applications. Their two-terminal structure provides advantages in terms of fabrication, mechanical flexibility, and reproducibility. However, due to their low responsivity, they require high driving voltages (>5V). Here, we propose a simple procedure for the design of high-performance, low-power, and flexible perovskite photodetectors by employing an assembled polymeric microbead monolayer. A large-area photonic crystal comprising transfer-printed polystyrene (PS) beads on poly(methylmethacrylate) (PMMA)/perovskite layers confines the electromagnetic field in perovskite. The significant increase in the photoluminescence characteristics of perovskite improves the responsivity, detectivity, and noise equivalent power to over 8.5 times. The polarization-insensitive light absorption of perovskite by the PS bead layer promotes excellent omnidirectionality with respect to the incident light at different angles. Furthermore, the mechanical durability of the flexible devices at a submillimeter bending radius (0.2 mm) is significantly improved by employing PMMA/PS layers. The resulting device performance exhibits excellent retention of 81.5% after 20 bending cycles. The proposed approach in the design of versatile micro-optical structures on perovskite paves the way in realizing highly deformable and efficient perovskite-based optoelectronics.

Omnidirectional and polarization-insensitive light absorption enhancement in an organic photovoltaic device using a one-dimensional nanograting

A novel poly-3-hexylthiophene (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) solar cell was designed with both the silver cathode and the organic layers structured into one-dimensional periodic patterns. Its optical behavior was investigated systematically by the finite element method. The numerical results indicate that a broadband, omnidirectional, and polarization-insensitive light absorption enhancement is realized by utilizing this structure. This is attributed to the simultaneous excitation of both plasmonic and photonic modes by particular structural designs. Moreover, the increased absorption allows for the use of very thin active layers, resulting in decreased losses of charge carriers transporting to the electrodes. Therefore, this proposal is expected to find potential applications in organic solar cells for improving the overall device performance.

LIGHT ABSORBER WITH AN ULTRA-BROAD FLAT BAND BASED ON MULTI-SIZED SLOW-WAVE HYPERBOLIC METAMATERIAL THIN-FILMS (Invited Paper)

Here we realize a broadband absorber by using a hyperbolic metamaterial composed of alternating aluminum-alumina thin fllms based on superposition of multiple slow-wave modes. Our super absorber ensures broadband and polarization-insensitive light absorption over almost the entire solar spectrum, near-infrared and short-wavelength infrared regime (500{2500nm) with a simulated absorption of over 90%. The designed structure is fabricated and the measured results are given. This absorber yields an average measured absorption of 85% in the spectrum ranging from 500nm to 2300nm. The proposed absorbers open an avenue towards realizing thermal emission and energy- harvesting materials.

Enhanced light absorption in thin-film tandem solar cells using a bottom metallic nanograting

We introduced a metallic nanograting at the bottom of thin-film tandem solar cells, and carried out an investigation into the light absorption in the top and bottom cells via the electromagnetic simulation. It indicates that broadband and polarization-insensitive light absorption enhancement can be obtained in the bottom cell, while the light absorption in the top cell remains unchanged by the influence of the added metallic nanograting. An overall carrier generation enhancement reaches as much as 60 % for both incident polarizations. This absorption enhancement can survive in a wide range of the cell thickness and the nanograting geometries, which enables us to reduce the thickness of the bottom cell with minimal impact on the light absorption. Thereby, this design could reduce the solar cell production cost, and meanwhile could enhance the solar cell efficiency by decreasing the light-generated carrier recombination rate.

Broadband light absorption enhancement in polymer photovoltaics using metal nanowall gratings as transparent electrodes

The authors investigate light absorption in organic solar cells in which indium tin oxide (ITO) is replaced by a new metallic architecture (grating) as a transparent electrode. Different from typical metal nanowire gratings, our gratings consist of metal nanowalls with nanoscale footprint and (sub)microscale height [Adv. Mater. 23, 2469 (2011)], thus ensuring high optical transmittance and electrical conductivity. Simulations reveal that a broadband and polarization-insensitive light absorption enhancement is achieved via two mechanisms, when such silver nanowall gratings are employed in P3HT:PCBM based solar cells. Overall absorption enhanced by ~23% compared to a reference cell with ITO electrode.

Absorption Enhancement in Plasmonic Solar Cells by Incorporation of Periodic Nanopatterns

ABSTRACTCurrently, the performances of thin film solar cells are limited by poor light absorption and carrier collection. In this research, large, broadband, and polarization-insensitive light absorption enhancement was realized via incorporation of different periodic nanopetterns. By studying the enhancement effect brought by different materials, dimensions, coverage, and dielectric environments of the metal nanopatterns, we analyzed the absorption enhancement mechanisms as well as optimization criteria for our designs. A test for totaling the absorption over the solar spectrum shows an up to ∼30% broadband absorption enhancement when comparing to conventional thin film cells.

Broadband Light Absorption Enhancement in Thin-Film Silicon Solar Cells

Currently, the performances of thin film solar cells are limited by poor light absorption and carrier collection. In this research, large, broadband, and polarization-insensitive light absorption enhancement was realized via integrating with unique metallic nanogratings. Through simulation, three possible mechanisms were identified to be responsible for such an enormous enhancement. A test for totaling the absorption over the solar spectrum shows an up to approximately 30% broadband absorption enhancement when comparing to bare thin film cells.