Luminescent solar concentrators utilizing stimulated emission

Optimization of amorphous silicon solar cells through photonic crystals for enhanced optical properties

Amorphous silicon solar cells have emerged as a promising technology for harnessing solar energy due to their cost-effectiveness and flexibility. However, their efficiency is constrained by low sunlight absorption resulting from the material's indirect band gap and intrinsic properties of amorphous silicon. This study employs theoretical modeling to investigate the impact of incorporating one-dimensional ternary photonic crystals (1D-Ternary-PCs) as anti-reflection coatings (ARCs) and one-dimensional binary PCs as back reflectors to enhance the optical properties of amorphous silicon (a-Si) solar cells. The investigation utilizes the COMSOL Multiphysics program, based on the finite element method (FEM), to simulate and analyze the optical characteristics of PC-enhanced a-Si solar cells. The modeling involves designing and optimizing ternary PC structures, followed by numerical simulations to assess their anti-reflection performance. Additionally, designing one-dimensional binary PCs optimized to create a photonic band gap within the transmitted spectrum to act as a back reflector. The study systematically examines the impact of various parameters such as layer thickness, refractive indices, and incident angles on the optical properties of PC-enhanced a-Si solar cells, offering insights into the potential of one-dimensional PCs as effective back reflectors and ARCs for enhancing light absorbance and overall efficiency.

Large area stimulated emission luminescent solar concentrators modelled using detailed balance consistent rate equations

Stimulated emission luminescent solar concentrators (SELSCs) have the potential to reduce escape cone losses in luminescent solar concentrators (LSCs). However, a functional SELSC is yet to be demonstrated. Previous numerical studies and detailed balance limits provide guidance, but they also contradict and likely overestimate performance and underestimate requirements. In this work, we introduce a rate-equation model with inversion requirements compatible with detailed balance limits and apply this model to the numerical modelling of window-sized SELSCs. We find that the optimal pump photon energy for both LSCs and SELSCs is 1.35 eV and the potential improvement of SELSCs over LSCs is found to be 19.3%. The efficiencies found are much lower than those specified in previous work due to the increase in Stokes shift required for a highly luminescent material. We also find that SELSCs are more attractive at higher matrix losses, that emission linewidths <0.05  eV are desirable, and that SELSC devices can potentially achieve performance equal to LSCs at low illumination levels and simultaneously exceed it by up to 16.5% at 1-sun illumination.

Detailed balance limits for inversion in solar-pumped lasers and allied systems

Solar-pumped lasers and optical amplifiers continue to draw research interest with advances in nanomaterials science and technology. Establishing accurate detailed balance limits for inversion in these systems is essential. In this Letter, we re-examine the threshold limits for inversion in broadband-pumped lasers, with reference to those provided by Roxlo and Yablonvitch [Opt. Lett.8, 271 (1983)OPLEDP0146-959210.1364/OL.8.000271], where they determined the minimum Stokes shift and the minimum ratio of pump band to emission band absorption constants-based on independent consideration of the emission at pump and emission frequencies. In contrast, the derivation here simultaneously accounts for emission in both the pump and emission bands, which in turn leads to a single consolidated inequality that serves to establish the revised threshold requirements for inversion. Upon applying this new unified relationship to solar-pumped devices, a large increase in the minimum required Stokes shifts for 1-sun devices, particularly at larger pump energies and smaller ratios of α_p0/α_e0, is found. The maximum possible efficiencies of solar-pumped devices are calculated using this new relation.

Characterization of Double-Doped Polymer Optical Fibers as Luminescent Solar Concentrators

This work reports on a diameter dependence analysis of the performance as luminescent solar concentrators of three self-fabricated polymer optical fibers (POFs) doped with a hybrid combination of dopants. The works carried out include the design and self-fabrication of the different diameter fibers; an experimental analysis of the output power, of the output irradiance and of the fluorescent fiber solar concentrator efficiency; a comparison of the experimental results with a theoretical model; a study of the performance of all the fibers under different simulated lighting conditions; and a calculation of the active fiber length of each of the samples, all of them as a function of the fiber core diameter. To the best of our knowledge, this paper reports the first analysis of the influence of the POF diameter for luminescent solar concentration applications. The results obtained offer a general perspective on the optimal design of solar energy concentrating systems based on doped POFs and pave the way for the implementation of cost-effective solar energy concentrating devices.

Gain investigation of Perylene-Red-doped PMMA for stimulated luminescent solar concentrators

Luminescent solar concentrators (LSCs) utilizing stimulated emission by a seed laser are a promising approach to overcome the limitations of conventional LSCs, with a significant reduction of the photovoltaic material. In our previous work, we demonstrated the principle of a stimulated LSC (s-LSC) and correspondingly developed a model for quantifying the output power of such a system, taking into account different important physical parameters. The model suggested Perylene Red (PR) dye as a potential candidate for s-LSCs. Here, we experimentally investigate the gain of PR-doped polymethyl methacrylate (PMMA) required for s-LSCs using a single pump wavelength (instead of the solar spectrum) as a proof of principle. The results found from the experiment are well matched with the previously developed numerical model except for gain saturation, which occurs at a comparatively small seed laser signal power. To investigate the gain saturation, two approaches were taken: investigating (i) spectral hole burning and (ii) triplet state absorption. Experimental investigation of spectral hole burning with PR dyes showed a small effect on the gain saturation. We developed a general state model considering triplet state absorption of the PR dyes for the second approach. The state model suggests that the PR dyes suffer from significant triplet state absorption loss, which obstructs the normal operation of the PR-based s-LSC system.

Influence of luminescent material properties on stimulated emission luminescent solar concentrators (SELSCs) using a 4-level system

The effect of various design and material parameters on the efficiency of stimulated emission-based luminescent solar concentrators (SELSCs) is studied numerically using a 4-level luminescent material containing concentrator. It is shown that the most efficient SELSCs have emission wavelengths of 1.5-1.8 µm, with a strong dependence on the Stokes shift. Depending on the parameters of the system, spontaneous emission is shown to nevertheless account for a significant fraction of potential energy generation. Assuming a propagation loss constant of -0.1m^-1, and a refractive index of 1.5, the optimal length of an SELSC is found to be ~1.5m. Given these losses and an efficiency target of 10% greater than traditional LSCs, the required material emission linewidth varies from 10 to 100nm, with maximum thicknesses of 3-30 µm. Further, when reflection and propagation losses are considered, a single laser pass is preferred over multiple passes. It is also shown that SELSCs are significantly less sensitive to luminescent quantum efficiency when compared to conventional LSCs due to the increased radiative emission rate.

Modeling of stimulated emission based luminescent solar concentrators

The efficiency improvement of luminescent solar concentrators (LSCs) necessary for practical realization is currently hindered by one major loss mechanism: reabsorption of emitted photons by the luminophores. Recently, we explored a promising technique for reducing reabsorption and also improving directional emission in LSCs utilizing stimulated emission, rather than only spontaneous emission, with an inexpensive seed laser. In this work, a model is developed to quantify the gain (i.e. the amount of amplification of a low power seed laser propagating through the solar-pumped concentrator) of stimulated-LSCs (s-LSCs) considering the effects of different important physical parameters. The net optical output power, available for a small PV cell, from the concentrator can also be determined from the model, which indicates the performance of s-LSCs. Finally, the performance of different existing material systems is investigated using literature values of the parameters required for the model, and a set of optimal parameters is suggested for practical realization of such a device.

Photonic microstructures for energy-generating clear glass and net-zero energy buildings

Transparent energy-harvesting windows are emerging as practical building-integrated photovoltaics (BIPV), capable of generating electricity while simultaneously reducing heating and cooling demands. By incorporating spectrally-selective diffraction gratings as light deflecting structures of high visible transparency into lamination interlayers and using improved spectrally-selective thin-film coatings, most of the visible solar radiation can be transmitted through the glass windows with minimum attenuation. At the same time, the ultraviolet (UV) and a part of incident solar infrared (IR) radiation energy are converted and/or deflected geometrically towards the panel edge for collection by CuInSe2 solar cells. Experimental results show power conversion efficiencies in excess of 3.04% in 10 cm × 10 cm vertically-placed clear glass panels facing direct sunlight, and up to 2.08% in 50 cm × 50 cm installation-ready framed window systems. These results confirm the emergence of a new class of solar window system ready for industrial application.