This PDF file contains the front matter associated with SPIE Proceedings Volume 12416, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The contribution focuses on a theoretical analysis of 2D multilayered halide perovskites, and their interfaces with 3D perovskites. At present, perovskite materials are mixed with each other in complex alloys and heterostructures, including 2D/3D compositions, combined with additives or protecting layers to improve their stability as well as assembled with carrier selective layers. The specificities of the mechanical properties of halide perovskites by comparison to classical semiconductors and the role played by large cations in the interlayer of the 2D perovskite are discussed.

The possibility of replacing lead in perovskites with other elements in 2D and 3D perovskites is explored. The most highly efficient perovskites are made with an inorganic-organic compound with lead. The influence on band structure, the density of states, and absorption coefficient are explored using first-principals density functional calculations. The advantages and disadvantages of 2D vs. 3D perovskites and their efficiency for energy conversion are also discussed. Ab initio DFT methods were used and implemented using a VASP software package. This research is important because perovskites solar cells are the most efficient solar cells currently studied by researchers, but they are prevented from being introduced to the market due to their instability. Perovskites are unstable and break down when they encounter things that they would commonly encounter during their application including moisture, high UV light, and excessive heat. When the perovskite structure starts to break down, lead is released into the environment.

The ultrashort time scale carrier dynamics of photoexcited carriers in semiconductor nanostructures is critical in controlling energy loss processes, which is necessary to realize advanced concept photovoltaic devices based on concepts such as hot carrier extraction. Here, we compare ensemble Monte Carlo (EMC) simulation of carrier dynamics in semiconductor multi-quantum well (MQW) structures with continuous wave photoluminescence studies performed in type I and type II InGaAs quantum wells. We compare the effects of including nonequilibrium phonon effects as well as the inclusion of intervalley scattering in the EMC simulations on the simulated carrier distribution functions in comparison with the PL studies. EMC analysis shows that reduced carrier cooling is predominantly due to nonequilibrium LO phonons. For type II systems, additional effects due to real space transfer and delocalization of the photoexcited holes occur.

Semiconductor nanowires (NWs) have shown robust hot carrier effects due to their small dimensions. Here, we study the cooling mechanisms of hot electrons in the time domain via transient absorption spectroscopy. Probe energies below the bandgap are used to determine the evolution of the carrier effective mass while probe energies above the bandgap track the conduction band occupation. From excitation intensity dependent measurements, we confirm that electron-hole interactions are a major cooling channel at large carrier density, given the high ratio of m_h/m_e of InAs. Our experiments indicate that this cooling channel is amplified in passivated core-shell NWs. We associate this effect with spatial carrier separation caused by Fermi-level pinning in unpassivated NWs. In core-shell NWs, bands are considerably more flat which increases radiative recombination and electron-hole scattering with the latter cooling the hot electron population. Our results highlight the advantages of carrier separation if high carrier densities are to be used for hot phonon bottlenecks.

Transferable III-V thin films, combined with light trapping structures, present several interests for photovoltaics: cost, material usage and weight reduction, flexible devices… To obtain such films, remote epitaxy consists in growing above a graphene covered III-V substrate, providing detachable mono-crystals. We report the fabrication of large-area graphene/GaAs substrates by a metal-assisted dry transfer with a high yield (<95%), reduced damage to the lattice, negligible doping, and stress relaxation. After the optimization of chemical etching steps, XPS reveals a residue-free surface with low oxidation levels compared to conventional transfers. Nucleation studies using MBE resulted in the formation of microcrystals, with partial alignment with the underlying GaAs(001).

In this paper, the electro-optical characteristics of the smallest-to-date GaAs-based multi-junction micro-photovoltaic devices (PVs) that can be used for ~850nm monochromatic light absorption will be presented. PV devices with circular single-aperture and aperture size of 30-150μm have been fabricated on semi-insulating GaAs substrate. The total number of light-absorbing junctions varies between one to three, and the layer structures are optimized to efficiently absorb a monochromatic light source at the wavelength of ~850nm. The light current-voltage characterization of these devices shows a linear scaling of the open-circuit voltage by increasing the number of active junctions, from 1.2V for single junction devices to ~3.6V for triple junction PVs. It has been observed that changes in the incident light density or the aperture size of the PV do not notably affect the photo-generated voltage. A maximum power conversion efficiency of 55% and fill factor of 84% is achieved for triple junction devices with aperture size of 150Νm, accordingly. However, it is shown that the peak efficiency drops to below 10% and fill factor reduces to 73% for devices with aperture size of 30μm. This is likely due to existence of non-radiative recombination centers near the mesa sidewall area that create shunt conduction paths and can adversely affect the photovoltaic performance of the device. This becomes worse for the smaller devices, as the device’s perimeter to area ratio increases proportionally. Overall, these results demonstrate the feasibility of fabrication of multi-junction micro-PVs for low-power sensing and energy storage application.

Renewable energy has been on the forefront of our efforts to stop climate change, with solar power being a major focus. Within a given day, solar cell performance is higher around noon and lower during morning and evening hours. To maximize the performance of solar cells, many installations use mechanical tracking arrangements thus adding significant costs while reducing reliability. To improve the efficiency and make them independent of seasonal and daily variation, a novel curved solar cell array contoured to the inside of a hemisphere in conjunction with a specially designed domed lenticular lens is proposed. By contouring the solar cell with a curvature matching the “Petzval curvature” of the full optical system, the efficiency can be increased significantly provided the resulting irradiance remains in balance within the manufactured specification limits. By using proper combinations of curvature and specially designed optical assembly, the need for mechanical systems can be eliminated. Optical modeling was performed to determine optimal curvature and the optimal optical system. Efficiency of the solar cells were measured over three days at two hour intervals, as a base line, and was found to vary from 11.5% to 18%. Then, the optical system consisting of a Fresnel lens was positioned over the curved solar cell array. A 14% increase in peak efficiency was measured. The efficiency during morning and late afternoon also increased significantly over the base line, confirming the benefit of this apparatus. This innovative approach has the potential to increase the efficiency and reduce the cost of future solar panel installations.

This paper describes experiments on having organized power transmission over optical fibers (Powerover- Fiber, PWoF) for a seismoacoutic seafloor module, consisting of a three-component geophone and a hydrophone. The experimental setup includes a fiber-optic information and energy cable, a photovoltaic optical energy converter, and seismic sensors based on intermolecular electron transfer. It is shown that the efficiency of the conversion depends on the optical power incident on the converter and load connected to it, so that optimal conversion regimes of operation are found out. The results of field tests of the experimental setup in the White Sea are also presented.

Despite the increasing flexibility of lead (Pb) based single perovskites for optical applications, the issue of stability and Pb toxicity is a major concern for realizing stable and durable devices. To overcome these drawbacks, it is very important to synthesize new, stable and non-toxic perovskite materials. In this work, we have synthesized and characterized a novel, stable, and lead-free organic-inorganic hybrid halide-based double perovskite (DP) material MA₂KBiCl₆ for the first time by facile one-step hydrothermal method. The structural characteristic of MA₂KBiCl₆ is observed at room temperature by the X-ray diffraction (XRD) technique which confirms the phase formation and is in agreement with the reference data. Furthermore, photoluminescence (PL) spectroscopy of synthesized material was performed at room temperature (300K) to observe its optical characteristics. An excellent photoluminescence phenomenon has been observed in the material due to band-to-band transition as well as phonon-assisted carrier recombination. To see the surface morphology we have done the scanning electron microscopy (SEM) at room temperature which indicates the good crystalline behaviour of the synthesized material. Also, MA₂KBiCl₆ DP exhibit promising absorption phenomena having a direct and indirect bandgap of 3.125 eV and 2.750 eV respectively. Moreover, the transmittance phenomenon has been observed from the Fourier transform infrared spectroscopy (FTIR). This novel finding on the non-toxic double perovskite material MA₂KBiCl₆ has opened up opportunities for sustainable development of various double perovskite materials for photovoltaic utility.

The lead-free metal trihalide perovskite material has been extensively studied due to its promising, and outstanding optoelectronic properties. Herein, we have studied the impact of alloying on CsSnBr₃ perovskite nanoparticles with reduced graphene oxide (rGO) on its structural and optical properties for its utility in solar cell devices. The formation of phase and highly crystalline behavior of the pristine CsSnBr₃ and rGO alloyed CsSnBr3 has been observed by the X-ray diffraction (XRD) technique. A direct bandgap of 1.81 eV and 1.75 eV has been calculated from the Tauc plot for CsSnBr₃ and rGO alloyed CsSnBr₃ respectively indicating a decrease in band gap due to rGO alloying. The photoluminescence (PL) plot represents a blue shift phenomenon in the PL peak of CsSbBr₃ after rGO alloying. Also, a decrease in full-width half maxima (FWHM) has been seen after alloying CsSnBr₃ with rGO which further indicates an increase in crystalline size and a decrease in grain boundaries. Furthermore, the surface morphology of rGO alloyed CsSnBr₃ has been noticed from scanning electron microscopy (SEM) images depicting a nano rod-like structure uniformly spread over the rGO sheet. This study suggests structural and optical tuning along with enhancement in properties of CsSnBr₃ after rGO alloying for its utility in the fabrication of high-performance and ultra-stable solar cell devices.