Photon Management Research Articles

Polarized and Directional Electroluminescence from Organic Light‐Emitting Devices by Using a Bifunctional Meta‐Electrode

AbstractOrganic light‐emitting devices (OLEDs) with polarized and directional emission are highly desired for their promising applications in optical imaging, optical communication, and immersive visual technologies. Existing implementation methods based on free space bulk optical elements suffer from significant power loss, limiting their practical applications. Here, a bifunctional meta‐electrode is proposed by integrating a metasurface consisting of Ag periodic corrugations onto the indium tin oxide (ITO) anode to simultaneously realize the functions of charge carrier injection and photon management in the OLEDs. Highly polarized and directional light emission is demonstrated while maintaining a high device efficiency using the meta‐electrode. The electroluminescence with a polarization extinction ratio of 5 is achieved by judiciously engineering the polarization‐dependent Purcell factor of the resonant cavity constructed by the meta‐electrode. Meanwhile, the directional light emission with a divergence angle of 10° can be obtained by the efficient out‐coupling of surface plasmon‐polariton mode. The light beam can be collimated in one direction by using 1D nanogratings and in two directions by using 2D nanopillars, respectively.

Unveiling Energy Conversion Mechanisms and Regulation Strategies in Perovskite Solar Cells.

Despite recent revolutionary advancements in photovoltaic (PV) technology, further improving cell efficiencies toward their Shockley-Queisser (SQ) limits remains challenging due to inherent optical, electrical, and thermal losses. Currently, most research focuses on improving optical and electrical performance through maximizing spectral utilization and suppressing carrier recombination losses, while there is a serious lack of effective opto-electro-thermal coupled management, which, however, is crucial for further improving PV performance and the practical application of PV devices. In this article, the energy conversion and loss processes of a PV device (with a specific focus on perovskite solar cells) are detailed under both steady-state and transient processes through rigorous opto-electro-thermal coupling simulation. By innovatively coupling multi-physical behaviors of photon management, carrier/ion transport, and thermodynamics, it meticulously quantifies and analyzes energy losses across optical, electrical, and thermal domains, identifies heat components amenable to regulation, and proposes specific regulatory means, evaluates their impact on device efficiency and operating temperature, offering valuable insights to advance PV technology for practical applications.

Mechanically robust and self-cleaning antireflective coatings for photovoltaic modules

As the conversion efficiency of solar cells approaches its theoretical upper limit, the importance of photon management in enhancing photovoltaic modules performance becomes paramount. One promising approach involves the application of antireflective coatings to the surface of the photovoltaic glass to improve its transmittance. However, balancing mechanical durability, self-cleaning characteristics, and optical performance for photovoltaic applications remains challenging. This study focuses on synthesizing a composite coating through the sol-gel method, aiming to achieve high optical transmittance and superior mechanical properties. Hollow silica nanoparticles (HSN) are employed to achieve a reduced refractive index, while a composite sol of zirconium dioxide (ZrO2) and titania (TiO2) is utilized to enhance mechanical strength and hydrophilicity. The prepared composite coatings demonstrate notable improvements, with the photovoltaic transmittance (TPV) increasing from 88.31 % to 94.03 % in the 300–1100 nm wavelength range, with peak transmittance reaching 98.01 %. Additionally, the coatings exhibited a pencil hardness rating of 3H alongside exceptional abrasion resistance, affirming their potential for enduring practical deployment. When compared to uncoated glass, modules integrated with these composite coatings showed a significant increase in short-circuit current density (JSC) by 1.28 mA cm-2 and in photoelectric conversion efficiency (PCE) by 0.70 %. These results highlight the composite coatings' capacity to enhance the conversion efficiency of photovoltaic modules significantly. By attempting to prepare anti reflective coatings with high mechanical strength and self-cleaning properties, this study is expected to make a valuable contribution to the advancement of sustainable and durable solar cell technology.

An optical study on the enhanced light trapping performance of the perovskite solar cell using nanocone structure

Photon management strategies are crucial to improve the efficiency of perovskite thin film (PTF) solar cell. In this work, a nano-cone (NC) based 2D photonic nanostructure is designed and simulated aiming at achieve superior light trapping performance by introducing strong light scattering and interferences within perovskite active layer. Compared to the planar PTF solar cell, the NC nanostructured device with 45 degrees half apex angle obtains highest short-circuit current density, which improved over 20% from 15.00 mA/cm2 to 18.09 mA/cm2. This work offers an alternative design towards effective light trapping performance using 2D photonic nanostructure for PTF solar cell and could potentially be adopted as the nano-structuring strategy for the future perovskite solar cell industry.

Nitrogen-doped graphene quantum dots/ polyvinyl alcohol nanocomposite for photon management: Application in CIGS photovoltaic cells

The efficiency (η) of copper indium gallium selenide (CIGS) solar cells has been hampered by absorption losses that happen within the ZnO and CdS layers. A photon downconversion layer created from polyvinyl alcohol (PVA) and nitrogen-doped graphene quantum dots (NGQDs) composite (NGQDs/PVA) was implemented on the top of the cell to overcome this obstacle. Notably, the NGQDs/PVA layers, prepared at spin speeds of 3000, 4000, and 5000 rpm, exhibited optimal characteristics, demonstrating superior light absorption at low wavelengths along with elevated transmittance at longer wavelengths. The η was found to be highest for the layer prepared at 4000 rpm, accompanied by elevated values of short-circuit current (Jsc), open-circuit voltage (Voc), and fill factor (FF). Consequently, Cell #2 incorporating the champion NGQDs/PVA layer outperformed all other CIGS photovoltaic cells, showcasing an impressive enhancement of 8.96 % in Jsc, 1.62 % in Voc, 2.03 % in FF, and an overall η of 11.51 %. This champion cell significantly improves the performance of CIGS photovoltaics.

Photon Management Enabled by Opal and Inverse Opal Photonic Crystals: from Photocatalysis to Photoluminescence Regulation.

Light is a promising renewable energy source and can be converted into heat, electricity, and chemical energy. However, the efficiency of light-energy conversion is largely hindered by limited light-absorption coefficients and the low quantum yield of current-generation materials. Photonic crystals (PCs) can adjust the propagation and distribution of photons because of their unique periodic structures, which offers a compelling platform for photon management. The periodicity of materials with an alternating refractive index can be used to manipulate the dispersion of photons to generate the photonic bandgap (PBG), in which light is reflected. The slow photon effect, i. e., photon propagation at a reduced group velocity near the edges of the PBG, is widely regarded as another valuable optical property for manipulating light. Furthermore, multiple light scattering can increase the optical path, which is a vital optical property for PCs. Recently, the light reflected by PBG, the slow photon effect, and multiple light scattering have been exploited to improve light utilization efficiency in photoelectrochemistry, materials chemistry, and biomedicine to enhance light-energy conversion efficiency. In this review, the fabrication of opal or inverse opal PCs and the theory for improving the light utilization efficiency of photocatalysis, solar cells, and photoluminescence regulation are discussed. We envision photon management of opal or inverse opal PCs may provide a promising avenue for light-assisted applications to improve light-energy-conversion efficiency.

Six-orders-of-magnitude-spanning dispersion measurement via Kalman filtering-aided white-light interferometry.

Dispersion plays a great role in ultrafast laser oscillators, ultrashort pulse amplifiers, and many other nonlinear optical dynamics. Therefore, dispersion measurement is crucial for device characterization, system design and nonlinear dynamics investigation therein. In this work, we demonstrate a versatile approach, i.e., Kalman filtering-aided white-light interferometry, for group delay dispersion (GDD) characterization. Extended Kalman filter is adopted to track the cosine-like interferogram, and to eliminate the unintended bias and the envelope, providing a nearly ideal phase retrieval and GDD estimation. The measurement range could span from tens of fs2 to tens of ps2, with an uncertainty of about 0.1%, enabling precise GDD measurement for diverse optical components, ranging from a millimeter-thick glass slide to highly dispersive chirped fiber Bragg gratings. Benefited by the simplicity, convenient setup, and easy operation as well as relatively low cost, this approach would help photonic device characterization, dispersion management and nonlinear dynamics investigation in the laboratory and work plant.

Luminescence Properties of an Orthorhombic KLaF4 Phosphor Doped with Pr3+ Ions under Vacuum Ultraviolet and Visible Excitation.

Fluorides have a wide bandgap and therefore, when doped with the appropriate ions, exhibit emissions in the ultraviolet C (UVC) region. Some of them can emit two photons in the visible region for one excitation photon, having a quantum efficiency greater than 100%. In a novel exploration, praseodymium (Pr3+) ions were introduced into KLaF4 crystals for the first time. The samples were obtained according to a high-temperature solid-state reaction. They exhibited an orthorhombic crystal structure, which has not been observed for this lattice yet. The optical properties of the material were investigated in the ultraviolet (UV) and visible ranges. The spectroscopic results were used to analyze the Pr3+ electronic-level structure, including the 4f5d configuration. It has been found that KLaF4:Pr3+ crystals exhibit intense luminescence in the UVC range, corresponding to multiple 4f → 4f transitions. Additionally, under vacuum ultraviolet (VUV) excitation, distinct transitions, specifically 1S0 → 1I6 and 3P0 → 3H4, were observed, which signifies the occurrence of photon cascade emission (PCE). The thermal behavior of the luminescence and the thermometric performance of the material were also analyzed. This study not only sheds light on the optical behavior of Pr3+ ions within a KLaF4 lattice but also highlights its potential for efficient photon management and quantum-based technologies.

Strain modulation in crumpled Si nanomembranes: Light detection beyond the Si absorption limit.

Although Si is extensively used in micro-nano electronics, its inherent optical absorption cutoff at 1100-nm limits its photonic and optoelectronic applications in visible to partly near infrared (NIR) spectral range. Recently, strain engineering has emerged as a promising approach for extending device functionality via tuning the material properties, including change in optical bandgap. In this study, the reduction in bandgap with applied strain was used for extending the absorption limit of crystalline Si up to 1310 nm beyond its intrinsic bandgap, which was achieved by creating the crumpled structures in Si nanomembranes (NMs). The concept was used to develop a prototype NIR image sensor by organizing metal-semiconductor-metal-configured crumpled Si NM photosensing pixels in 6 × 6 array. The geometry-controlled, self-sustained strain induction in Si NMs provided an exclusive photon management with shortening of optical bandgap and enhanced photoresponse beyond the conventional Si absorption limit.

Knitting-stitching bifacial metafabrics with switchable thermal and moisture transmissibility for multimodal dynamic personal thermoregulation.

Smart textiles with thermal and moisture management functionalities are highly desirable for enhancing human comfort and reducing weather-related health issues. However, achieving high-performance thermoregulatory fabrics that simultaneously exhibit reversible cooling and heating functions, and effective sweat management through industrial fabrication, remains challenging due to the lack of compatible textile technologies capable of manipulating hierarchical structures. Herein, a robust thermal and moisture-managing metafabric (TMM fabric) with a stitching-interlaced-knit structure is developed using industrialized machine knit technology. Unlike layered fabrics, this knitted structure endows the TMM fabric with different appearances on its two opposite surfaces for reversible photon management, while integrating these surfaces into an all-in-one construction using interlacing yarns. The interlacing yarns also serve as pathways for heat and moisture transmission, enhancing thermal conduction and water transportation. A coupling agent-assisted zinc oxide nanoprocessing is further applied to the cooling surface of the TMM fabric to improve solar reflectivity. The bifacial TMM fabric demonstrates on-demand radiative/evaporation cooling and photo-thermal heating capacities by simply flipping the fabric, achieving an effective temperature regulation of over 17 °C. Furthermore, the TMM fabric shows desirable electro-thermal performance, enabling it to protect the human body from harsh low-temperature conditions of -18 °C. Moreover, the TMM fabric demonstrates good breathability and robust mechanical properties. This facile structural design as a paradigm provides a new insight for producing scalable, robust and efficient personal thermoregulation textiles adaptive to superwide temperature changes using well-engineered textile structures.

Textured anti-reflection and down-conversion composite functional films for high-efficiency solar cells.

Advances in high-efficiency solar cells introduce photon management challenges, including the difficult texturization of flat surfaces and low photon utilization at short wavelengths. While bifacial crystalline silicon solar cells have a front pyramid structure and SiN x layers reduce reflections, managing photons on the flat backside remains a challenge. To enhance light utilization, a soft nanoimprint technique was utilized to create pyramid micro-structured polyurethane films doped with europium (Eu3+) complex. These films, which possess anti-reflection and down-conversion properties, can be applied externally to various high-efficiency solar cells without compromising electrical performance. Research on the backside of bifacial PERC solar cells revealed that the optimal composite functional film increases the integrated current by 5.70%, with a 1.27% gain from down-conversion effects. This specialized film presents a novel approach to interface matching for different types of solar cells.

(Invited) Mulitjunction III-V Semiconductors for Photo-Electrochemical Hydrogen Production: Recent Progress in Efficiency, Durability, and Cost

Photo-electrochemical (PEC) hydrogen production is a route to carbon-free fuel that combines light absorption and water electrolysis into one device. Challenging targets for solar-to-hydrogen (STH) efficiency, durability, and semiconductor absorber costs must be realized for this approach to be economically competitive with other hydrogen production pathways. Research on PEC hydrogen production at the National Renewable Energy Laboratory (NREL) has focused on III-V semiconductor absorber materials because their tunable bandgaps, high photon conversion efficiencies, and ability to make multi-junction structures have resulted in the highest STH efficiencies yet demonstrated. This talk will focus on recent NREL results showing progress toward PEC hydrogen production efficiency, durability, and cost targets. Specifically, we have been able to improve theoretically achievable STH efficiency through bandgap engineering in multijunction devices. Photon management strategies to close the gap between theoretical and measured STH efficiency will also be discussed. Durability remains a significant challenge for III-V materials in a PEC environment. We will describe modifications to the semiconductor surface and the electrolyte constitution that can make the photoabsorber less susceptible to photocorrosion during operation. Finally, we will present preliminary results on III-V PEC materials synthesized via hydride vapor phase epitaxy, an alternative route to high-efficiency photoelectrodes that could potentially have much lower costs than the metalorganic vapor phase epitaxy method traditionally used. These improvements have yielded III-V PEC devices that are close to the STH efficiency target (17% vs. 25%) while the demonstrated durability and cost are still considerably far from their target values.

Design and Simulation of a High‐Efficiency CuInS2Thin‐Film Solar Cell with a Thin CIS Current Augmenter

Ternary chalcopyrite compound cupper indium disulfide (CuInS2)‐based photovoltaic cells are designed and numerically computed. In this design, n‐CdS and p++‐MoS2have been used as window and back surface field (BSF) layers, respectively. The modeled n‐CdS/p‐CuInS2/p++‐MoS2device provides power conversion efficiency (PCE) of 24.6% withJSCof 26.98 mA cm−2,VOCof 1.05 V, and fill factor (FF) of 86.93%. This efficiency is ≈60% higher the than n‐CdS/p‐CuInS2single heterostructure. Furthermore, the use of a second CuInSe2(CIS) absorber layer between CuInS2absorber and MoS2BSF layer significantly enhances the short‐circuit current. As a result, the current expressively improves to 38.48 mA cm−2, yielding an efficiency of 32.4%. The greater built‐in potential in absorber/BSF interface is attributed to the highJSCandVOC, causing the increment of efficiency. Besides, the photon management by Bragg reflector with 90% back and front reflectance recycling effect further increases the PCE to 36.1%. This work indicates the prospects of CuInS2solar cells with a CuInSe2current augmenter and MoS2BSF layers for the fabrication of efficient CuInS2solar cells.

Self-adaptive photonic thermal management based on a flexible metasurface

As a new technology that uses thermal radiation to transmit the heat of objects to the universe through the transparent window of the atmosphere, radiative cooling has the advantages of zero energy consumption and zero pollution. However, most of the reported radiative cooling materials cannot sense the change of the ambient temperature and make corresponding thermal regulation behaviors independently. To address this issue, we propose a novel design based on flexible metasurface to realize the passive self-adaptive radiative cooling. By depositing flexible thermal expansion material in the sandwich structure, the metasurface can switch between ‘ON’ and ‘OFF’ states of radiative cooling function with the change of ambient temperature, and effectively control the absorption and reflection of electromagnetic waves in the atmospheric window, realizing flexible transformation of radiation cooling and insulation. Meanwhile, the cooler can achieve extremely low absorptivity across the entire solar spectrum for daytime cooling. This study is expected to provide practical solutions for the development of modern energy-efficient buildings.

Simultaneous all-angle self-collimation for both light and sound in phoxonic crystals

We report the all-angle dual optical and acoustic waveguides in defect-free phoxonic crystals. The realization of this function relies on dual flat open equal-frequency contours (EFCs) enabling all-angle self-collimation for both optical and acoustic waves. For incident angles within 85°, both light and sound can propagate simultaneously along the propagation direction without diffraction in the proposed defect-free structure. As a potential application of our work, a compact 3 dB phoxonic Y-shaped beam splitter is designed and numerically demonstrated. The coexistence of all-angle optical and acoustic self-collimation allows a new potential possibility to realize integrated management of photons and phonons with an ultracompact footprint size.

Lanthanide doped NaYF4 core@multi-shell nanoparticles: Synthetic strategy for emission in divergent spectral regions

We present the use of lanthanide doped NaYF4 based core@multiple-shell nanoparticles as optical materials showing merged possibilities of engineered photon management processes. We have successfully synthesized and characterized series of NaYF4 core@shell@shell@shell nanomaterials in which the core parts were doped with NIR absorbing/emitting lanthanides (i.e., Nd3+, Yb3+, and Tm3+) to benefit from the complete separation of peristatic quenching processes connected to the interaction with solvent and/or ligand molecules. Followed by covering with an inert shell, Pr3+ ions were doped for VIS-to-UVC up-conversion in the next layer , and finally covered with yet another un-doped protecting shell. The obtained materials were characterized by the means of morphology, crystal structure and spectroscopic properties, with the emphasis put on the measurements in the UVC and NIR spectral regions. The obtained results showed the interesting possibility of merging within designed nanoparticles architectures both UVC light generation for future therapeutic purposes and NIR emission for deep tissue optical imaging diagnostics.

Multi-band tunable strongly nonreciprocal thermal radiation in topological edge state coupled mode

Violating Kirchhoff's law of thermal radiation can break the reciprocity constraints on spectral emissivity and absorptivity, which provides new capabilities for managing photonic heat flow and fundamentally improves energy harvesting systems' efficiency. Currently, most micro-nano structures that violate Kirchhoff's law are mainly confined to single- or dual-band models, significantly limiting applications such as photonic energy conversion and thermal management. Here, a scheme is proposed for a topological one-dimensional photonic crystal heterostructure consisting of multiple photonic crystals and Weyl semimetals, and its absorptivity and emissivity are theoretically calculated by the transfer matrix method. The results show that the multi-band nonreciprocity that completely violates Kirchhoff's law can persist over broad angular and frequency ranges without requiring any external magnetic field via tuning the relevant parameters. Furthermore, the electric field distribution reveals that the formation of such multiple bands originates from the coupling between topological edge states, and the significant enhancement of the local field near the interface of the heterostructure provides favorable conditions for the realization of strong nonreciprocity. Our work may contribute to the design and development of multiband nonreciprocal devices for energy conversion and thermal management and may also provide design ideas for multiband reciprocal absorbers, filters, optical switching, etc.

Influence of perovskite thickness on the performance of silver-doped NaZnBr3 perovskite solar cells using SCAPS software

The absorbing layer thickness is a crucial parameter that significantly impacts the performance of perovskite solar cells (PSCs). In this study, we investigated the influence of the thickness of absorbing layer on the performance of silver-doped NaZnBr3 perovskite solar cells using the one-dimensional solar cell capacitance simulator (SCAPS-1D) software. The absorbing layer thickness was varied in the range of 0.1 to 1.3 µm. The initial solar cell after simulation gave an open-circuit voltage (Voc) of 1.174 V, short circuit current density (Jsc) of 14.012 mA/cm2, fill factor (FF) of 79.649%, and the power conversion efficiency (PCE) of 13.101%. For the optimized thickness of the perovskite layer of 1.0 µm, the following solar cell characteristics were obtained: Voc = 1.197 V, Jsc = 18.184 mA·cm–2, FF = 79.110%, and PCE = 17.215%. A 31% and 30% increase of the PCE and Jsc, respectively, was observed for the optimized device parameters as compared to the initial ones. Such finding confirms the premise for excellent photon management and enhancement of PSCs performance by selecting the thickness of absorbing layer.

Photonic management of silicon nanocylinder arrays to enhance photovoltaic performance

The light–matter interaction of subwavelength and periodic silicon (Si) nanostructures strongly correlates with their geometrical features, resulting in them being highly unsuitable for the practical development of Si-based photovoltaic applications. In this study, the concepts of effective medium and retrieval methods are needed to deal with the subwavelength periodic dielectric structure. Using finite-difference time-domain simulations, we study the interactions of electromagnetic radiation with a square array of dielectric rods parallel to the incident light, and the effective optical properties such as refractive index, permittivity, and permeability are calculated. Furthermore, the electric field distributions are also plotted for a deeper understanding of the energy changes within Si nanocylinder arrays (SiNCAs) under different incident wavelengths of radiation. By employing calculated optimized SiNCAs for the construction of hybrid solar cells, improved cell performances showing a conversion efficiency of 13.79% are demonstrated, with further estimation by electrical chemical measurements for a better understanding of the carrier transition. These are numerically and experimentally interpreted by the involvement of excellent light-trapping effects, delivering a method to design correlated photovoltaic devices.

Full spectrum photon management of photonic crystal-based aerogels to achieve the multiscale multiphysics regulations and optimizations of PV-TE/T systems

Multicomponent coupling is an effective way to achieve full-spectrum solar energy utilization. However, conventional multicomponent coupled PV systems are deficient in the rational distribution of full-spectrum sunlight. In this study, a photovoltaic-thermoelectric/thermal (PV-TE/T) system with photonic crystal-based aerogels (PCA) is proposed based on a novel strategy for efficient full-spectrum solar energy utilization. Then, a multiscale multiphysics theoretical model is developed to study the effects of full-spectrum selectivity characteristics of PCA on the performance of the PCA-based PV-TE/T system. Comparative analyses between stand-alone PV system, tandem PV-TE system, normal PV-TE/T system and PCA-based PV-TE/T system are performed. The full-spectrum selectivity characteristics of PCA allows the PCA-based PV-TE/T system to not only increase the maximum achievable photon current density of PV component by 2.39%–3.00%, but also to increase the heat source (light absorption) for TE component by at least 2609.84%. When the concentration increases to 20, the electrical efficiency of the stand-alone PV system is already 0%, and the electrical efficiency of the tandem PV-TE starts to decrease to 27.01%. As for the PCA-based PV-TE/T system, the maximum electrical efficiency of the PCA-based PV-TE/T system is 32.64% at the concentration of 93. Meanwhile, the thermal collector of the PCA-based PV-TE/T system absorbs 6277.5 W/m2 of thermal energy. Therefore, the PCA-based PV-TE/T system not only has a high efficiency of full-spectrum solar energy utilization, but also is applicable to higher concentrations, which offers the system the potential for further cost reductions.