The application of a luminescent down-shifting (LDS) layer has been proposed as a method for improving the poor spectral response (SR) of solar cells to short-wavelength light. The LDS layer absorbs ...photons, typically in the 300–500
nm range, and re-emits them at a longer wavelength where the photovoltaic (PV) device exhibits a significantly better response. This paper reviews the progress in this area over the last three decades, starting from early experiments that yielded promising results but being limited by the luminescent materials available at the time, to modern materials that exhibit higher luminescent quantum efficiencies and better photostability. The candidate materials are considered and their potential is reviewed for a wide range of PV technologies. A particular opportunity is the ability to use the existing polymer encapsulation layer of certain PV technologies as a LDS layer as well.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
One of the most important elements of a luminescent solar concentrator (LSC) is the host material. In this work, we investigate the key optical properties of eight polymeric host matrices. ...Poly(methyl methacrylate) (PMMA) and polycarbonate (PC) based formulations exhibited the lowest internal absorbance within the spectral range of the absorption and emission bands of a red‐emitting fluorescent organic dye (Lumogen Red 305). The dye absorbance was dependent on the host matrix and was higher for the PC‐based formulations than the other polymers. However, two different doping concentrations were used, and the higher concentration led to the absorption of more than 90 % of the incident photons within the absorption band of the dye in all cases. The overall optical efficiency with respect to edge emission from 60 mm×60 mm×3.2 mm LSCs varied within an absolute value of 1 % for the eight host matrices investigated. The best result achieved in terms of optical efficiency was 8.9 % for PMMA‐ and PC‐based hosts.
Edge emission intensity from LSCs! The optical performance of eight different host materials for luminescent solar concentrators (LSCs) is investigated. Poly(methyl methacrylate) (PMMA) and a polycarbonate (PC) based formulations result in the best optical efficiency of 8.9 %.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The inclusion of luminescent material in the ethylene vinyl acetate (EVA) encapsulation layer of multicrystalline silicon (mc-Si) photovoltaic modules offers a production-ready method for the ...improvement of their short-wavelength (λ) spectral response and overall conversion efficiency. Several luminescent materials and mixtures thereof were evaluated for this purpose in an EVA matrix, including perylene and violanthrone dyes and a novel ligand sensitised europium complex. The external quantum efficiency of mc-Si modules can be greatly improved in the region of 300 nm <; λ <; 400 nm via luminescent down-shifting (LDS) of the incident light. In the best-case scenario, an increase in efficiency of 0.3% absolute is reported for a 59-cm 2 minimodule. The LDS technology cannot only be simply transferred to a standard production line with no added layers and/or manufacturing processes but can be used to color photovoltaic (PV) modules for architectural purposes as well.
We describe the preparation and optical characterisation of a coronene tetracarboxylate salt (CS) in polyvinyl alcohol (PVA) thin film solutions processed from water, neat or mixed with varying ...ratios of a europium tris(hexafluoroacetylacetoanto) diaquo complex Eu(hfac)3(H2O)2. Neat CS‐PVA showed not only well‐defined fluorescence peaks but also a long‐lived phosphorescence emission, persisting for more than 1 second. Interaction between the CS and EuIII molecules, mediated by means of carboxylate coordination to the EuIII, was attained by simple incorporation into the PVA polymer matrix and resulted in energy transfer from the coronone antenna to the europium centre. Under various blend ratios of CS and the EuIII complex, total photoluminescence quantum yields of typically around 30 % were achieved. The straightforward processing of this type of self‐assembled chromophore‐lanthanide system into a luminescent polymer film offers potential for application to other chromophores, lanthanides and polymers.
Coronene‐tetracarboxylate salt shows interaction with Eu(hfac)3 when blended together in spin‐coated films of PVA. Excitation of the coronene gives Eu emission through energy transfer, achieved by a simple in situ assembly process.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Perovskite solar cells (PSCs) demonstrate excellent power conversion efficiencies (PCEs) but face severe stability challenges. One key degradation mechanism is exposure to ultraviolet (UV) light. ...However, the impact of different UV bands is not yet well established. Here, we systematically study the stability of PSCs on the basis of a methylammonium lead iodide (CH3NH3PbI3) absorber exposed to (i) 310–317 (UV-B range) and (ii) 360–380 nm (UV-A range), under accelerated conditions. We demonstrate that the investigated UV-B band is detrimental to the stability of PSCs, resulting in PCE degradation by more than 50% after an exposure period >1700 sun-hours. This finding is valid for architectures with a range of electron transport layers, including SnO2, compact-TiO2, electron-beam TiO2, and nanoparticle-TiO2. We also show that photodegradation is apparent for high, as well as for low illumination intensities of UV-B light, but not for illumination with UV-A wavelengths. Finally, we show that degradation of PSCs is preventable at the cost of a small fraction of photocurrent by using UV-filtering or luminescent downshifting layers.
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IJS, KILJ, NUK, PNG, UL, UM
The soiling of photovoltaic (PV) modules can significantly reduce their energy yield unless a mitigation strategy is employed. One solution investigated in this work involves the implementation of a ...passive self-cleaning superhydrophobic top cover. To this end, superhydrophobicity was induced by hot-embossing random microtextures on a highly transmissive and photostable fluorinated ethylene propylene (FEP) film. The impact of fabrication parameters (hot-embossing force and temperature) on achieving high contact angles (> 150°) and low roll-off angles (< 10°), which characterizes a surface as superhydrophobic, were investigated. It was found that a minimum threshold force of at least 15 kN and 5 kN must be used to achieve superhydrophobicity for processing temperatures of 270 °C and 280 °C respectively. Meanwhile at the highest investigated temperature of 290 °C, any force within the investigated range of 500 N to 50 kN suffices. The best fabrication parameters were identified (5 kN at 280 °C), resulting in a contact angle of 156 ± 1° and a roll-off angle of 8 ± 3°. When incorporated into a silicon PV mini-module, the addition of the textured FEP film enhances the short circuit current density (JSC) by 1.1%. Moreover, the self-cleaning properties of the textured FEP films result in a recovery ratio of 93.6% (in terms of JSC), which is significantly greater than that of the reference glass encapsulated PV mini-module (61.1%).
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•Random microtextures produce highly transmissive and superhydrophobic FEP surface.•Minimum threshold force to achieve superhydrophobicity identified (5 kN).•Easier to obtain superhydrophobicity at higher fabrication temperatures.•Relative 1.1% enhancement of power conversion efficiency of PV modules.•Self-cleaning recovery of 93.6% in terms of JSC achieved with best case sample.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Inspired by the transparent hair layer on water plants Salvinia and Pistia, superhydrophobic flexible thin films, applicable as transparent coatings for optoelectronic devices, are introduced. Thin ...polymeric nanofur films are fabricated using a highly scalable hot pulling technique, in which heated sandblasted steel plates are used to create a dense layer of nano‐ and microhairs surrounding microcavities on a polymer surface. The superhydrophobic nanofur surface exhibits water contact angles of 166 ± 6°, sliding angles below 6°, and is self‐cleaning against various contaminants. Additionally, subjecting thin nanofur to argon plasma reverses its surface wettability to hydrophilic and underwater superoleophobic. Thin nanofur films are transparent and demonstrate reflection values of less than 4% for wavelengths ranging from 300 to 800 nm when attached to a polymer substrate. Moreover, used as translucent self‐standing film, the nanofur exhibits transmission values above 85% and high forward scattering. The potential of thin nanofur films for extracting substrate modes from organic light emitting diodes is tested and a relative increase of the luminous efficacy of above 10% is observed. Finally, thin nanofur is optically coupled to a multicrystalline silicon solar cell, resulting in a relative gain of 5.8% in photogenerated current compared to a bare photovoltaic device.
Superhydrophobic highly transmissive polymeric films inspired by hair‐covered plant surfaces are fabricated using a scalable hot pulling technique. The flexible self‐cleaning films are characterized by low reflection, high transmission, and high amount of forward scattering. These exceptional optical properties are exploited for improving the efficiency of organic light‐emitting diodes and silicon‐based solar cells.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Micron‐scale textures at the front surface of solar modules have been reported to improve the current generation by both enhancing light in‐coupling as well as by reducing light out‐coupling via ...back‐reflection, similar to the retroreflective effect. Whereas the general working principle and advantages of these textures have been described previously, here, the interplay of the reflection properties of different substrates with the enhancement effects is analyzed for textures of conical geometry. The study takes into consideration the incident light of arbitrary angle of incidence as well as the overall energy yield. Supported by optical simulations, periodic micro‐cone textures were optimized and prototyped based on direct laser writing and a scalable replication process. Micron‐scale textures with cones of various aspect ratios were examined on mono‐crystalline silicon (c‐Si) solar cells; an optimum aspect ratio of 0.73 was identified. This moderate aspect ratio is suitable for large‐scale replication, while showing near‐zero surface reflection and excellent light trapping. An increase in energy yield of up to 8% was calculated for the case of micro‐cone textures at the front surface of commercial alkaline‐etched c‐Si solar cells. Moreover, the excellent optical properties of the micro‐cone textures were highlighted by improving the power conversion efficiency (PCE) of a Cu(In,Ga)Se2 (CIGS) thin‐film solar cells from 20.2% to 20.9%. A comparable PCE improvement has been achieved by conventional MgF2 antireflection coatings, but the angular stability and in turn the energy yield of the micro‐cone textures is much higher.
Micron‐scale textures applied to the front surface of solar modules enhance the transmission to the underlying solar cells and trap light reflected from the solar cells. A systematic experimental study of conical micro‐textures is performed, focusing on the aspect ratio. The interaction between the texture and solar cell is investigated in detail, and the angle‐stable performance enhancement on different photovoltaic devices is demonstrated.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Photovoltaic devices based on Cu(In,Ga)Se2 (CIGS) absorbers exhibit poor response to short-wavelength (λ) photons, mainly due to the parasitic absorption of the commonly used zinc oxide window and ...cadmium sulphide (CdS) buffer layers. In this work, it is shown that the energy content of these photons can be better harnessed if the encapsulation layer of modules is doped with luminescent materials. It is shown that the luminescent down-shifting (LDS) of short-λ photons increases the external quantum efficiency (EQE) of CIGS devices by up to 25% absolute in the range 300–380nm and by up to 40% absolute in the region 300–460nm, for devices with 50-nm- and 100-nm-thick CdS layers, respectively. Overall, the short-circuit current density (JSC) of CIGS devices covered with luminescent encapsulation improved by ΔJSC=0.6% for violet-doped EVA and up to ΔJSC=1.8% for a violet–yellow dye mixture. By experimenting with devices of different CdS thicknesses and short-λ EQE profiles, it is suggested that CIGS PV modules equipped with LDS layers must be optimised as a system and all photoactive components of the device be considered in parallel.
► CIGS solar cells were encapsulated using luminescent ethylene vinyl acetate layers. ► The short-wavelength response was greatly improved via luminescent down-shifting. ► The photocurrent and efficiency increase as a result. ► This enhancement is achieved for devices with different cadmium sulphide thickness. ► Coloured devices can be manufactured with this technique.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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