Light Trapping Structures Research Articles

High broadband light absorption in ultrathin MoS2 homojunction solar cells.

Transition metal dichalcogenides (TMDCs) have been proposed as light absorber materials for ultrathin solar cells. These materials are characterized by their strong light-matter interaction and the possibility to be assembled into devices at room temperature. Here, we model the optical absorptance of an ultrathin MoS2 absorber embedded in different designs of a 1D optical cavity. We find that up to 87% of the photons contained in the 300-700 nm range of the AM1.5G spectrum can be absorbed employing MoS2 absorbers as thin as 10 nm sandwiched between a h-BN top layer and an optically thick Ag reflector. An h-BN/MoS2/h-BN/Ag cavity produces 0.89 average absorptance for a 57-nm-thick MoS2 slab and it also maximizes the absorption of extremely thin absorbers, between 1 and 9 nm. We also model a possible large-scale device on a glass substrate combined with indium-tin oxide (ITO) whose absorptance is comparable to the other presented structures. The high broadband absorption in these light-trapping structures is caused by the amplification of the zeroth Fabry-Perot interference mode. This study demonstrates that light absorption in ultrathin solar cells based on nanometric TMDC absorbers can compete with conventional photovoltaic technology and provides different simple optical designs to choose from depending on the electronic characteristics of the TMDC junction.

Multi-angle wide-spectrum light-trapping nanofiber membrane for highly efficient solar desalination

Solar-driven interfacial water evaporation has been recognized as one of the promising methods to solve the problem of fresh water shortage. However, due to the dependence of the incident angle of light, the light absorption performance of materials in practical applications is limited. Herein, a three-dimensional (3D) light-trapping structure was constructed by zinc oxide nanowires within carbon-based nanofiber membrane using electrospinning technology, hydrothermal growth and magnetron sputtering techniques for multi-angle wide-spectrum light absorption. It has excellent average absorption (>90 %) performance in a wide range of angles (0°- 80°), and a rapid photo-thermal conversion capacity (70℃ after 30 s solar illumination), which are higher than that in previous literature. The average absorption of light from 200 to 2500 nm can reach 95 %. Under 1 sun irradiation (1 kW m-2), the solar evaporation rate can reach 1.73 kg m-2h-1, and the evaporation efficiency can reach 94 %. The multi-angle wide-spectrum light-absorption of the membrane might provide a promising strategy for collecting water in other practical applications.

Conformal PDMS films for strengthening flexibility and retaining absorption in pyramid ultra-thin c-Si solar cells

Ultra-thin c-Si solar cells with the advantages of flexibility, translucence and portability are weakened in the performance of flexibility due to the surface light trapping structure, which reduces its future application potential. In this work, we designed a conformal PDMS film on the Si surface with pyramid structure to greatly inhibit the stress concentration on the surface and enhance the flexibility of ultra-thin c-Si solar cells. The maximum decrease of the Si surface stress can reach 71.19%, from 232.07 N/m2 of the pyramid structure to 66.86 N/m2 of the conformal PDMS film. In this process, it is found that at the stress concentration position, the conformal PDMS film can change the included angle of stress directions from 180° to 90° for reducing the probability of Si wafer rupture. In addition, the refractive index change in the vertical direction of the conformal PDMS film is more moderate, which can achieve the reflection reduction to improve the light absorption from 91.36% to 94.17%. Using multi physical simulation to evaluate the mechanical and photoelectric properties, the ultra-thin c-Si solar cell with conformal PDMS film has the best comprehensive performance, with the maximum surface stress of 74.59 N/m2 and the power conversion efficiency (PCE) of 19.04%, which is reduced by 49.49% and increased by 4.27%.

Enhanced light trapping effect of hierarchical structure assembled from flower-like cobalt tetroxide and 3D-printed structure for efficient solar evaporation

Compared with conventional two-dimensional (2D) structure, three-dimensional (3D) solar steam generators have presented a considerably higher evaporation rate due to their structure superiority. As an emerging field, 3D printing technology has been attached by significant attention due to its feasibility and designability in the fabrication of micro-nano structures. Herein, inspired by natural light-trapping structures, a novel hierarchical structure assembled from flower-like cobalt tetroxide and 3D-printed stent is prepared. Based on the geometrical light trapping effect, both the flower-like structure in cobalt tetroxide and the hollow morphology in 3D-printed stent can significantly enhance the solar absorption and conversion efficiency through multiple reflection-incidence processes. Since the wetting direction in the cylindrical structure is always from the edge to the center, there will be a large number of salt particles at the edge of the cylinder falling by the virtue of gravity, thus achieving a high salt tolerance, and this process is illustrated by molecular dynamics simulation. Along with the rapid photo-thermal response in the solar spectrum, this 3D-printed hierarchical structure coated with flower-like cobalt tetroxide has achieved a high steam generation rate of 2.028 kg m-2h−1 under one sun irradiation (1.0 kW/m2) and excellent decontamination ability for organic dye-containing solution. Meanwhile, the desirable steam generation rate can maintain an average value of more than 1.8 kg·m-2h−1 for long time. This 3D-printed solar evaporator is highly efficient and salt-tolerant, attributed to the enhanced geometrical light-trapping and artificial channel-array structure, presenting an effective solution for enhancing solar absorption and conversion.

Tungsten-Disulfide-Based Ultrathin Solar Cells for Space Applications

Two-dimensional (2-D) materials, such as transition metal dichalcogenides (TMDCs), are strong candidates for space photovoltaics as they are very lightweight, flexible, and resilient to ionizing radiation. Here, an ultrathin tungsten disulfide (WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) based photovoltaic cell with photon management features has been modeled, with performance improvement from enhanced absorption. Our photovoltaic model consists of a 200 nm thick WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based heterojunction solar cell, similar to the HIT (heterojunction with intrinsic thin layer) solar cell structure, together with a light trapping grating structure and an antireflection coating layer. The photovoltaic cell with an optimized 1-D grating light trapping structure and an appropriate antireflection dielectric coating was demonstrated to give an efficiency above 23% under the AM0 solar spectrum in our model—comparable with other single-junction space photovoltaic cells. The material properties are taken directly from experimentally observed results; the proposed device architecture with additional optical features is based on experimentally fabricated devices and structures and is expected to be resistant to ionizing radiation in the space environment. Our results show that our TMDC-based photovoltaic system with light trapping and antireflection coating is a strong candidate for space photovoltaic applications.

Self-Powered and Fast Response MoO3/n-Si Photodetectors on Flexible Silicon Substrates with Light-Trapping Structures

Flexible photodetectors are considered to be extremely important flexible electronic components of the future. In this work, flexible silicon (F-Si) substrates with inverted pyramidal light-trapping structures were prepared by wet chemistry and metal-assisted etching. Due to the better ability of the light-trapping structure to capture light, the F-Si substrate was capable of absorbing more than 90% of visible light and can be in bending angles of over 180°. On the basis of F-Si substrates with light-trapping structures, self-powered MoO3/n-Si heterojunction flexible photodetectors (FPDs) were prepared to achieve high responsivity (0.696 A/W@980 nm), detectivity (1.59 × 1013 jones), and fast response (τr/τd of 5.35 μs/0.97 μs). The devices also showed effective photoresponse in the wavelength range from 405 to 980 nm. Moreover, the Si-based FPDs exhibited a favorable response to high-frequency light, with a response frequency of up to 100 kHz. The photocurrent of the device maintained more than 95% of the initial value after 200 bending cycles. In addition, Si-based FPDs are successfully applied to fingertip heartbeat tests for human health data extraction. The development of Si-based FPDs provides a path for flexible electronic devices.

Achieving efficient power generation by designing bioinspired and multi-layered interfacial evaporator

Water evaporation is a natural phase change phenomenon occurring any time and everywhere. Enormous efforts have been made to harvest energy from this ubiquitous process by leveraging on the interaction between water and materials with tailored structural, chemical and thermal properties. Here, we develop a multi-layered interfacial evaporation-driven nanogenerator (IENG) that further amplifies the interaction by introducing additional bionic light-trapping structure for efficient light to heat and electric generation on the top and middle of the device. Notable, we also rationally design the bottom layer for sufficient water transport and storage. We demonstrate the IENG performs a spectacular continuous power output as high as 11.8 μW cm−2 under optimal conditions, more than 6.8 times higher than the currently reported average value. We hope this work can provide a new bionic strategy using multiple natural energy sources for effective power generation.

67 GHz light-trapping-structure germanium photodetector supporting 240 Gb/s PAM-4 transmission

A light-trapping-structure vertical Ge photodetector (PD) is demonstrated. In the scheme, a 3 μm radius Ge mesa is fabricated to constrain the optical signal in the circular absorption area. Benefiting from the light-trapping structure, the trade-off between bandwidth and responsivity can be relaxed, and high opto-electrical bandwidth and high responsivity are achieved simultaneously. The measured 3 dB bandwidth of the proposed PD is around 67 GHz, and the responsivity is around 1.05 A/W at wavelengths between 1520 and 1560 nm. At 1580 nm, the responsivity is still over 0.78 A/W. A low dark current of 6.4 nA is also achieved at − 2 V bias voltage. Based on this PD, a clear eye diagram of 100 GBaud four-level pulse amplitude modulation (PAM-4) is obtained. With the aid of digital signal processing, 240 Gb/s PAM-4 signal back-to-back transmission is achieved with a bit error ratio of 1.6 × 10 − 2 . After 1 km and 2 km fiber transmission, the highest bit rates are 230 and 220 Gb/s, respectively.

An ultra-flexible silicon substrate with light-trapping structures: The application for visible-NIR photodetectors

Flexible substrates have been widely used in Visible-NIR photodetectors in recent years. Flexible silicon wafers were prepared by alkali etching. Pyramids with reflectivity of 11.8%, inverted pyramid with reflectivity of 7.9% and nanowire with reflectivity of 1.9% light-trapping structures were prepared by low concentration alkali etching, one-step Cu-MACE and Ag-MACE, respectively. In addition, PEDOT: PSS films doped with 5 wt% DMSO successfully presented the highest conductivity of 580 S·cm−1. The PEDOT: PSS/UF-Si PDs with different light-trapping structures were prepared by spin-coating PEDOT: PSS films. Comparing the optoelectronic performance of different light-trapping structures of the photodetector, the PEDOT: PSS/UF-Si NWs device exhibited the best optoelectronic performance. The photoresponse range is 300–1100 nm and the responsivity at the peak of 650 nm is 0.62 A·W−1. Furthermore, bending measurements are performed on PEDOT: PSS/UF-Si NWs PDs to evaluate the bending performance of the flexible PDs. For PEDOT: PSS/UF-Si NWs PDs with a bending radius of 5.3 mm and a bending cycle of 500, the responsitivity of the device demonstrates very small degradation.

Transparent Quasi-Random Structures for Multimodal Light Trapping in Ultrathin Solar Cells with Broad Engineering Tolerance.

Waveguide modes are well-known to be a valuable light-trapping resource for absorption enhancement in solar cells. However, their scarcity in the thinnest device stacks compromises the multiresonant performance required to reach the highest efficiencies in ultrathin devices. We demonstrate that enriching the modal structure on such reduced length-scales is possible by integrating transparent semiconductor/dielectric scattering structures to the device architecture as opposed to more widely studied metallic textures. This phenomenon allows transparent quasi-random structures to emerge as strong light-trapping candidates for ultrathin solar cells, given that their broad scattering profiles are well-suited to exploit the increased number of waveguide modes for multiresonant absorption enhancement. A thorough study of the design space of quasi-random textures comprising more than 1500 designs confirms the superiority of transparent structures over a metallic embodiment, identifies broad and flexible design requirements to achieve optimal performances, and demonstrates photon harvesting capabilities leading to 20% efficiency with an 80 nm GaAs absorber. Our light-trapping strategy can be applied to a wide range of material systems and device architectures, is compatible with scalable low-cost fabrication techniques, and can assist current trends to reach the highest efficiencies in ever-thinner photovoltaics.

Optical studies and validation of multidimensional hybrid metamaterial embedded light trapping structure for p-Si/n-ZnO based thin c-Si solar cell

ABSTRACT This paper deals with one competent light trapping structure of metamaterials embedded p-Si/n-ZnO-based thin solar cell assisted by different simulation studies. Through this article, the author exposed the credibility of ZnO as multidimensional material with dual utility to serve as anti-reflective coating with active material of this heterojunction solar cell. Additionally, dielectric metamaterial like silica nanoparticles on top of the structure enhanced the photon cultivation efficiency of the device. Further through this work, the author tries to validate the simulated structure in real world by the process of simple fabrication technique, which also offers same optical responses already given by theoretical studies. This investigation also confirms the metamaterial property of the monolayer silica nanoparticles in higher angle of incidence of light, which validates its utility in solar cell where injection of photon is needed throughout the day..

Broadband absorption enhancement in carbon-based perovskite solar cell with a composite light trapping structure

In this work, a composite light-trapping strategy based on Ag@SiO2 nanoparticles embedded inside the active layer and an antireflection coating on the top surface is proposed to obtain broadband absorption improvement in carbon-based perovskite solar cells (C–PSCs). The effects of geometrical parameters, including the radius and period of Ag nanoparticles, the thickness of the protective SiO2 shell and the thickness of the antireflection coating, on the light absorption are investigated using the finite-difference time-domain (FDTD) method. Simulation results illustrate that nearly full absorption of light can be achieved with the optimized structure parameters for a 600 nm thick perovskite layer using the composite light-trapping scheme. The short-circuit current density (JSC) exhibits an improvement of 24.8% relatively compared to the C-PSC without light management. The proposed composite light-trapping structure allows improved light utilization and saved material consumption in C–PSCs.

Towards high-efficiency Al-BSF c-Si solar cell with both superior omnidirectional and electrical performance by modulating the tilt angle of quasi-periodic inverted pyramid arrays

Seeking efficient light trapping structures with both superior omnidirectional and electrical performance is always on the way for increasing electrical energy output of c -Si solar cell over a wide range of light incident angle (θ). Here, tile angle (δ) of quasi-periodic structure arrays is systematically modulated from 35.9° to 72.8° on diamond-wire-sawn (DWS) c -Si by a simple and cost-effective Cu and Ni co-assisted chemical etching way followed by a post treatment. Interestingly, compared with the conventional micro pyramid (MP), the optimized inverted pyramid (IP) like arrays with a δ of 64° possess both lower light reflectance and carrier recombination, leading to a corresponding solar cell with a higher efficiency (∼19.67%) than that of MP based counterpart (∼19.31%). Moreover, during the increase of θ, the external quantum efficiency (EQE) of 64° IP based cell drops much more slowly than that of MP based one by properly adjusting the relative position of the structure arrays and incident light, indicating its omnidirectional property. Simultaneously, a maximum relative enhancement of electrical output power approaching ∼5.8% in the θ range of −90°–90° is achieved on 64° IP based cell compared to the MP based one, the mechanism behind which is further explained by optical simulation. The above finds pave a new way to increase the electrical energy output in a simple and cost-effective way. • Tilt angle control of quasi-periodic IP was achieved by varying Cu and Ni ratio. • 0.36% absolute increase in solar cell efficiency was made based on 64° IP. • ∼5.8% relative increase of output power was achieved on 64° IP based cell. • Mechanism behind omnidirectional performance was explained by optical simulation.

Random inverted pyramid textured polydimethylsiloxane radiative cooling emitter for the heat dissipation of silicon solar cells

Radiative cooling is a promising passive cooling phenomenon. For the heat dissipation of silicon solar cells, radiative cooling emitters require high transmittance in the wavelength range of 300–1100 nm and high emissivity in the range of 8–13 μm. In this paper, a simple and low-cost coating and embossing process is proposed to texture the surface morphology of the PDMS film. A radiative cooling emitter is prepared with a random inverted pyramid-like light-trapping structure on the surface. The experimental results show that the transparency and radiative cooling performance of textured polydimethylsiloxane films are improved by 2.1% and 2.7%, respectively. When using a polished Al mirror as the substrate, the radiative cooling temperature difference and net radiative cooling power are increased to 12.8 ℃ and 103 W·m−2, respectively. By employing it as a solar cell radiator, the radiative heat dissipation power of the solar cell is increased by 67 W·m−2, and the working temperature is reduced by over 17 ℃. An improvement in photoelectric conversion efficiency of 1.02% is achieved. It is demonstrated that the texturing treatment also improves the hydrophobicity of the polydimethylsiloxane film. The film is more applicable for radiative cooling emitters that are directly exposed to the atmosphere in outdoor environments.

Modeling free-carrier absorption in ultrathin III-V solar cells with light management.

Ultrathin III-V solar cells with proper light management have become more attractive than their optically thick counterparts as they are less expensive and lightweight, can maintain photon absorption, and have high radiation tolerance for space-related applications. Comprehensive optical modeling efforts have provided pathways to improve device efficiency in ultrathin GaAs solar cells with light trapping structures. Usually, the absorption mechanism known as free-carrier absorption (FCA) is ignored in these models due to the ultrathin layers and the direct bandgap of GaAs. This manuscript reports the significance of considering FCA as a parasitic loss caused by the optical enhancement in highly doped non-active layers between the ultrathin solar cell and backside light trapping structures. We model FCA based on Drude theory in a p-type AlGaAs layer behind ultrathin GaAs solar cells with a planar mirror and cylindrical gratings. Our results show that, depending on the AlGaAs thickness and doping concentration, free carriers will absorb transmitted photons and reduce the backside reflectance, degrading the current and voltage output from ideal conditions. One example shows that for a 300 nm-thick GaAs solar cell, the Ag mirror's peak reflectance decreases nearly 12% when the AlGaAs back layer is 800 nm-thick at a doping concentration of 4x1019 cm-3. Notably, the cylindrical grating designs with 38.5%, 46.5%, and 64.9% AlGaAs coverage resulted in an absolute efficiency reduction of 0.6%, 1.8%, and 2.9% at a doping concentration of 4x1019 cm-3, respectively. This novel study demonstrates that FCA in non-active layers must be properly addressed in the device design to progress the efficiency of ultrathin III-V solar cells with light trapping structures.

Cation disorder engineering yields AgBiS2 nanocrystals with enhanced optical absorption for efficient ultrathin solar cells

Strong optical absorption by a semiconductor is a highly desirable property for many optoelectronic and photovoltaic applications. The optimal thickness of a semiconductor absorber is primarily determined by its absorption coefficient. To date, this parameter has been considered as a fundamental material property, and efforts to realize thinner photovoltaics have relied on light-trapping structures that add complexity and cost. Here we demonstrate that engineering cation disorder in a ternary chalcogenide semiconductor leads to considerable absorption increase due to enhancement of the optical transition matrix elements. We show that cation-disorder-engineered AgBiS2 colloidal nanocrystals offer an absorption coefficient that is higher than other photovoltaic materials, enabling highly efficient extremely thin absorber photovoltaic devices. We report solution-processed, environmentally friendly, 30-nm-thick solar cells with short-circuit current density of 27 mA cm−2, a power conversion efficiency of 9.17% (8.85% certified) and high stability under ambient conditions.

Wide-angle and broadband solar absorber made using highly efficient large-area fabrication strategy

High performance and cost-effective solar absorbers are crucial for various optical applications, such as solar collection and thermophotovoltaic devices. This study designs and experimentally demonstrates a wide-angle and broadband solar absorber. The proposed absorber is composed of tapered polyimide substrate and Al-Cr-SiO2-Cr-SiO2 thin-film based on the optical interference of the multilayer thin film and excited magnetic resonance of light-trapping structures. The composite process of the colloidal lithography method and magnetron sputtering is employed for efficient fabrication in a large area. The average absorbance is more than 93% from 300 nm to 2500 nm and shows an angular tolerance of up to 60°. The high efficiency and large-area fabrication capability demonstrated by the proposed solar absorber presents future application potential in flexible solar collection devices.

Micro/Nanostructures for Light Trapping in Monocrystalline Silicon Solar Cells

Due to the ongoing depletion of fossil energy, alternative energy‐sources and their respective conversion technologies have become very essential. An inexhaustible and clean energy form, which is already widely used, is solar energy. However, despite much progress in recent decades, due to the limitations of materials and manufacturing technology, the ability of solar cells to convert light into electrical energy is still not very high. Enhancing light absorption and reducing electric loss are the keys to improving the overall conversion efficiency of solar cells and reducing raw material costs. The former can be achieved by using micro/nanostructures and other surface features, while the latter can be realized by surface passivation. Researchers have developed different silicon‐surface texturing methods to fabricate random or periodic micro/nanostructures on the surface of silicon wafers. Thanks to the special and efficient light‐trapping effects of silicon micro/nanostructures, both full angle and wideband light absorption can be achieved. Different passivation methods and materials have also been widely studied, which helps to improve the surface recombination of photogenerated carriers caused by light trapping structure and significantly enhance the power conversion efficiency of Si solar cells. In this work, theoretical studies of enhanced light‐trapping in micro/nanostructures are introduced. In addition, several advanced methods for preparing micro/nanostructures on the surface of monocrystalline silicon are discussed. These can be classified as top‐down and bottom‐up approaches. Furthermore, passivation methods for micro/nanostructures on the surface of monocrystalline silicon solar cells are reviewed, including chemical passivation and field‐effect passivation. Finally, advantages and disadvantages of the micro/nanostructure preparation technologies, and light‐trapping effects of the micro/nanostructures, which were fabricated using these manufacturing technologies were summarized. Moreover, the effects of different passivation technologies on the optical properties and electrical properties of these micro/nanostructures are studied. An outlook of expected and emerging research directions for monocrystalline silicon solar cells concludes this study.

Evaluation method of the light-trapping structure for a transparent thin-film silicon solar cell with low-illuminance condition

Transparent hydrogenated amorphous silicon (a-Si:H) thin-film solar cells were fabricated for building-integrated photovoltaic (BIPV) windows, and light-trapping structures were formed on aluminum-doped zinc oxide (ZnO:Al) front electrodes to increase the output current and power under low-irradiance conditions in buildings. The degree of light-trapping was controlled by varying the etching time for texturing the ZnO:Al electrodes. As the etching time increased from 5 to 20 s, the surface area and average haze increased from 102.02 to 116.27 μm2, and 3.4 to 14.6% in the absorption wavelength range of 400–600 nm, respectively. The introduction of the light-trapping structure can increase the photogenerated current but causes defects in the cell. The current and defect density both depend on the light intensity; the highest power conversion efficiency of the cell was obtained in different light-trapping structures depended on the light intensity. To evaluate the light-trapping effect independent of the light intensity, we theoretically derived the effective absorbance and current density loss parameters using rate equations, which were in good agreement with the measurements. The presented methods can be applied to various thin-film solar cells requiring light-trapping structures to effectively utilize low-illuminance conditions.

Preparation and properties of AZO/PS/AZO tri-layer transparent conductive film with a light-trapping structure

The light-trapping structure is an effective method to increase solar light capture efficiency in the solar cells. In this study, Al-doped ZnO (AZO)/polystyrene (PS)/AZO tri-layer transparent conductive film with light-trapping structure was fabricated by magnetron sputtering and liquid phase methods. The structural, optical and electrical properties of the AZO films could be controlled by different growth conditions. When the sputtering pressure of the under-layer AZO film was 0.2 Pa, the discharge voltage was around 80 V, which was within the optimal process window for obtaining AZO film with high crystallinity. The optimal under-layer AZO film had a large surface roughness and a very low static water contact angle of 75.71°, promoting the relatively uniform distribution of PS spheres. Under this sputtering condition, the prepared AZO/PS/AZO tri-layer film had the highest crystallinity and least point defects. The highest carrier concentration and Hall mobility are 3.0 × 1021 cm-3and 5.39 cm2 V-1 s-1, respectively. Additionally, a transparent conductive film with the lowest resistivity value (3.88 × 10-4 Ω cm) and the highest average haze value (26.5%) was obtained by optimizing the process parameters. These properties were comparable to or exceed the reported values of surface-textured SnO2-based as well as ZnO-based TCOs films, making our films suitable for transparent electrode applications, especially in thin-film solar cells.