This PDF file contains the front matter associated with SPIE Proceedings Volume 12150, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Alloying semiconductor nanocrystals with impurity can stabilize their phase with modulation of their morphology, lattice structure, photophysical and electronic properties which enhance their suitability towards solar cells and light-emitting diodes (LEDs). Herein we sought to substitute Mn²⁺ in CsPbI₃ nanoparticles (NPs) to overcome the phase transformation issue as well as to tune the electronic and optical properties of this perovskite material. The phase of the alloyed CsPbI₃ NPs was stabilized endowing high crystalline quality which can be clearly seen in X-ray diffraction (XRD). XRD plot depicts that impurity peaks arise in the case of CsPbI₃ NPs while the phase of Mn²⁺ alloyed NPs was stabilized upto 1 month. The decrease in lattice parameter values from 6.019 Å to 5.987 Å has been observed for pure CsPbI₃ and alloyed CsPbI₃ NPs respectively attributed to the reduction of the size of the cubic phase crystal structure due to the introduction of small size Mn²⁺ in place of large-sized Pb²⁺. The decrement in the lattice parameter further confirms the alloying of CsPbI₃ NPs with Mn²⁺. The absorption and emission peaks were tweaked in the synthesized CsPbI3 NPs after alloying which can be observed from the absorption spectrum and photoluminescence (PL). Alloying of CsPbI₃ NPs with Mn²⁺ leads to shifting in bandgap from 1.70 eV to 1.79 eV, PL peak from 671 nm to 654 nm, and absorption spectrum from 645 nm to 637 nm which suggest the tailoring of its novel properties. This investigation suggests the suitability of Mn²⁺ alloyed CsPbI₃ NPs in the area of optoelectronics.

The MorphoColor concept for highly efficient colored solar modules aims to improve the acceptance of those modules in visible areas like roofs and facades. The core of the MorphoColor technology is the combination of a structured substrate with a spectrally selective reflecting layer stack. The work presented within this manuscript investigates the effect of using an aperiodic substrate structure whose characteristic feature size is in the same order of magnitude as the wavelength of visible light. Representative pseudo-aperiodic structures were arrangedusing rigorous coupled-wave analysis. By combination of these structures with a layer stack, a fully wave optical model of this realization of the MorphoColor concept could be established. The characteristic feature width and height have been varied in this model, resulting in lower limits for the efficacy of the concept in both parameters. For slanted incidence, a significant change of the reflected spectrum was observed. To explore this effect, a model representing infinite feature sizes was developed by independently combining the effects of a refractive system with equal properties to the one used within the first model and a plain layer stack. The comparison of results obtained from both methodes showed that the usage of small features leads to additional effects that can be attributed to the interaction of structure and layer stack. The magnitude of these effects increased with increasing incident angle on the surface and leads to a reduced spectral selectivity of the reflection.

Manipulation of light was proved to be an efficient strategy to improve light harvesting efficiency in solar energy conversion. Inverse opal (IO) photonic structures are among the most promising materials, which permit light manipulation, thanks to their ability to slow down light at specific wavelengths and localize it within the dielectric structure. However, the generation, the control and, in particular, the practical utilization of these narrow spectral range ‘slow photons’ remain highly challenging and relatively underexplored. In this work, we report the ability not only to generate slow photons in the visible range by synthesizing highly ordered IO TiO₂ photonic structures, but also to control and tune their wavelengths, by varying lattice parameters (pore sizes), such that they can be efficiently utilized by the composite bismuth (Bi)-based semiconductor for visible light photocatalysis. Photocatalytic experiments revealed a 70% increase in efficiency in all IO structures compared to the corresponding non-structured compact film. In addition, a 20% increase in efficiency was observed when the photonic stop band gap as well as its blue and red edges were accurately tuned to match the electronic absorption of the Bi-based photocatalyst. Our choice of IO synthesis parameters and tuning strategies enabled us to generate, control and transfer the energy of slow photons from IO TiO₂ to the composite visible light-responsive photocatalyst for highly amplified photoactivity. This work opens new possibilities for the practical utilization of slow photon effect under visible light in various solar energy conversion applications.

A lossless solar cell operating at the Shockley-Queisser (S-Q) limit generates an open-circuit voltage (V_OC) equal to the radiative limit. At V_OC, the highly directional beam of photons from the sun is absorbed and subsequently externally reemitted into a 4π solid angle, providing a large photon entropy loss. Moreover, due to many total internal reflections and low internal radiative efficiency, a lot of light is lost in nonradiative recombination events. In our research, we perform a nanophotonic optimization of a semiconductor nanowire geometry with a top microlens in order to decrease the photon entropy loss and to increase the photon escape probability for the nanowire, therefore increasing the output voltage. The optimization leads us to a maximum V_OC of 1178 mV which is 141 mV higher than the radiative limit and 172 mV lower than the ultimate limit. The photon entropy loss is also studied fundamentally from the thermodynamics point of view to better understand where the entropy is generated during the absorption-emission processes.

Personal radiative heat regulation by photonic engineered textiles can help contribute to a more sustainable cooling and heating energy consumption in buildings by expanding the range of comfortable ambient conditions. Here, we propose various dual-mode photonic fabric designs (dynamic and static) that provide thermal regulation in both cold and hot environments. In the first design, we utilize metal-coated monofilaments arranged in a hexagonal geometry within a yarn and stimuli-responsive polymer actuator beads, in this way benefiting from the infrared (IR) photonic effect (or plasmonic gap) to control the wide-band transmission of thermal radiation and to provide for a sharp, dynamic response (Δτ = 0.9). The second design is based on metal microspheres randomly dispersed in a shape memory polymer membrane. The dynamic switching is achieved via a shape memory polymer matrix that responds to environmental changes. This design capitalizes on the strong scattering properties of metallic microspheres, leading to a strong modulation of reflectance (Δρ = 0.55) as a function of the volume fraction. The third design is a Janus-yarn fabric composed of an asymmetric structure, leading to dual emissivity characteristics. The strong emissivity contrast (Δε = 0.72 ) is achieved by utilizing metallic and dielectric fibers within the yarn; here, static switching is achieved via fabric flipping.

Considering the specific solar-thermal and optoelectronics applications of metamaterials, broadband absorbers with near-perfect absorption, tunability, and subwavelength dimensions are in high demand. Plasmonic metasurface absorbers have been found to be band-limited due to resonant plasmonic excitations, thus leading to exploration of materials with high broadband absorption, along with salient features of robustness to environmental degradation and thermal stability. In order to attain broadband absorptance, materials having higher values of attenuation constant (imaginary part of refractive index) are employed so that loss mechanism can be introduced for the operational frequency. We have carried out full-wave numerical simulations to design a highly efficient, metasurface-based light absorber with MIM (Metal-Insulator-Metal) configuration. The insulator layer minimizes reflection by trapping light and acting as a Fabry–Perot cavity between two metal layers, and the thick ground plane blocks transmission. The sandwiched insulator layer is of silica, while the metal layers are of a refractory-metal-nitride (ZrN), having a melting point of 2980 °C. The thermal stability of the entire absorber can be extended by coating a thin layer of Hafnium oxide (HfO₂). The proposed design has been optimized in terms of geometrical parameters, exhibiting an average absorptance of 95% for optical regime (400-800 nm), and 89.40% for ultra-broadband spectrum of 400-2000 nm. The study includes detailed analyses in terms of reflectance, transmittance, absorptance and free-space impedance-matching. The proposed ultrathin absorber has an overall height of 250 nm, is polarization-insensitive, angle-insensitive, and simple to fabricate with a high tolerance for fabrication errors. Moreover, a design for an emitter is proposed with a view to realize solar thermophotovoltaic (STPV) systems for solar energy harvesting. The emitter is designed in a way so as to have maximum efficiency for PV cells with a bandgap of 1.4 eV.

In recent years, Cesium lead tri-halide based wide energy gap inorganic perovskites becomes as an emerging material for novel photovoltaic and optoelectronic devices due to their room temperature stability. Herein, synthesis and characterization of CsPbX₃ (X= Cl & Br) quantum dots (QDs) have been performed to examine the structural, photophysical and electronic nature. X-ray diffraction (XRD) pattern indicates the high crystalline behavior of these synthesized compounds. Photoluminescence (PL) plots for these synthesized compounds correspond to the emission of Blue and Green color for CsPbCl₃ and CsPbBr₃ respectively. Further, the theoretical calculation has been also performed using Density functional theory (DFT) to validate our experimental results. Optimization has been done to bring the geometry in the ground state and lattice parameter has been obtained for CsPbCl₃ (5.58 Å) and CsPbBr₃ (5.82 Å) compounds which are consistent with the experimental results. Electronic band structure shows a direct bandgap behaviour for CsPbCl₃ (3.07 eV) and CsPbBr₃ (2.29 eV) compounds. Moreover, to examine the optical behavior of these QDs, the optical absorption coefficient has been computed. The optical behavior of these QDs shows significant optical absorption in both visible and ultraviolet regions. The calculated results using DFT show a very good agreement with our experimental characterized results. This study suggests applications of these QDs as a promising compound for Blue and Green LEDs.

A class of semiconducting materials namely inorganic Cesium (Cs)-based halide perovskites has attracted the research society due to their interesting electronic and optical behavior creating the interest of researchers to explore these materials in the domain of optoelectronics. In this context, red-emitting CsPbI₃ quantum dots (QDs) exhibiting unique optical and electronic properties are of great interest to explore. Here, we have investigated the optical and electronic properties of CsPbI₃ QDs by utilizing density functional theory (DFT) study with experimental insight. The morphological investigation of CsPbI₃ QDs provide a lattice parameter (a) value of 6.031 Å (a=b=c) with volume 219.365 ų. The calculated value of the lattice parameter from X-ray diffraction (XRD) is 6.079 Å which is in match with the theoretically calculated lattice parameter value. A sharp luminescence around 1.85 eV can be seen from the photoluminescence (PL) plot indicating the red-emitting behavior of CsPbI₃ QDs. Band structure calculation was carried out to envisage the electronic properties. An energy gap of 1.38 eV has been computed at the middle point of the Brillouin zone having a direct bandgap semiconducting nature. Furthermore, the absorption coefficient has been evaluated to study the optical behavior of CsPbI₃ QDs. The observed spectrum shows its presence in the visible region. Also, the edge of the absorption plot around 1.36 eV indicates the bandgap of CsPbI₃ QDs is in agreement with the energy gap computed from the band structure. These computational results along with experimental insight suggest that this material can be utilized in the domain of optoelectronics and solar cells.

In a series of previous articles [1], we have described phenomena that can be grouped under an integrating term as Giant Photoconversion. This designation covers discoveries and innovations in the field of silicon photovoltaics obtained mainly at the nanoscale. In this paper, we describe how to modulate the crystal lattice of the silicon wafer by burying in its interior a nanolayer with a specific crystallinity. Theoretical background has been recently proved by using mass production machines usually in service in the micro electronic industry. The new phenomena appear in a buried nanolayer of a silicon metamaterial having a specific crystalline phase and called SEG-Matter (Secondary Electron Generation – Matter). We have conceived a design and related manufacturing of new devices for high efficiency solar cells using our experimental results. The technology can be seen as a relatively simple development of the conventional c-Si cell manufacturing process completed by an amorphizing ion implantation and related thermal treatment. Both can be integrated in a production line. An original protocol has been developed first by a laboratory production on small dimension cells (a square 2 cm) in the Photonics Systems Laboratory of the Strasbourg University, then pursuit on 4-inch c-Si wafers in the LAAS CNRS in Toulouse and finally on standard c-Si wafers of the SEGTON AdT Company. The proof of concept of such solution have been recently done on commercial-sized wafers of crystalline silicon having a square 6-inch format. We obtained an increase in PV efficiency of about 2%.

A nondestructive insight into properties of nanoscale Si-layered system buried within a crystalline wafer is possible due adequate numerical analysis of dielectric functions and optical parameters. The investigation and development were made on an example of the heavily doped and/or highly excited Si:P. The comparison of predicted and measured performances was made on high efficiency bi-facial silicon solar cells.