Solar Window Research Articles

Solar power windows: Connecting scientific advances to market signals

Recent materials advances have enabled researchers to envision and develop highly efficient, partially transparent photovoltaic (PV) prototypes, exposing a potentially large and untapped market for solar energy: building integrated (BI) solar powered windows. In this perspective, we assess the case for market deployment of BIPV windows, specifically intended for commercial U.S. high-rise buildings. Research and development on solar powered windows has been predicated on the hypothesis that sunlight-to-electrical power conversion efficiency (PCE) and device cost per unit area are the key figures of merit that might drive market adoption. Here we investigate the market landscape and desirability for solar powered windows by identifying and evaluating the customer needs for the commercial high-rise building window market. In the course of this assessment, we performed 150 interviews with experts across the value chain for commercial windows. We found that the market forces are complicated by a misalignment of incentives between the end users of BIPV windows and the key decision makers for building projects that could incorporate this technology. Our assessment leads us to frame new figures of merit for BIPV windows that address the underlying needs of prospective customers as well as technical metrics for energy generation. We finally discuss one possible direction for BIPV window technology in which photovoltaics are integrated with switchable windows. Here, the integrated PV converts visible and infrared light transmission into useable electricity enabling standalone, self-powered active windows that can potentially address market needs for smart windows, thereby enabling a pathway for BIPV window deployment.

Review and Potential Development of Solar Window Technology and Feasibility Study in Urban Area, Hong Kong as Case Study

Net Zero Energy Building (NZEB) has been a rising topic in recent years, the route to achieve NZEB through renewable energy generation with the adaptation of solar window is explored. Literature review with current market research on the technology are studied and consolidated. Transformation from the current semi-transparent to future visibly transparent solar window is observed. Potential development of modular design with Wireless Power transfer is suggested for wide application of solar window. In the light of the large potential of solar window, feasibility study is conducted to analysis the application of the technology in Hong Kong context in term of the climate and installation criteria due to the Feed-In-Tariff (FiT). Solar analysis of solar resource availability and electricity generation are evaluated and simulated by Radiance using the morphologies of Central, Hong Kong as case study. Equations are developed for setting up selection criteria and estimating the suitable area for installation. 40.1% of solar insolation on an unobstructed horizontal plane was identified as threshold for installation in Hong Kong and the minimum installation is estimated to be 50 m2 in order to be cost effective

Functional Third Components in Nonfullerene Acceptor-Based Ternary Organic Solar Cells

ConspectusNonfullerene acceptors (NFAs) represent the latest breakthrough in organic solar cells (OSCs), which significantly outperform the long benchmark OSCs with fullerene derivative acceptors. In addition to binary bulk heterojunction (BHJ) OSCs, multicomponent, in particular ternary BHJ strategy has attracted tremendous interests due to the realization of broadened coverage of solar spectrum while maintaining easy processing compared to tandem OSCs. Subsequently, ternary OSCs containing NFA(s) have provided exciting opportunities to the promising field and achieved great progress in power conversion efficiencies (PCEs) over 17%. Inspired by the recent progress, in this account, we focus on the ternary OSCs containing NFA(s), share our view of the topic and aim to provide guidelines for material selections in designing successful ternary OSCs—toward the cornerstone of 20% PCE in the near future.In this Account, we first discuss the principle of OSCs—working mechanisms, including charge transfer and energy transfer that govern the charge dynamics. Moreover, the promising functional roles of the third components in NFA OSCs are highlighted at the following the sequence: (1) Absorption sensitizing—the additional component plays a key role in broadening the solar cell absorption window and thus promising in improving the photocurrent in the ternary active layer, especially when employing a near-infrared material NFA as the third component. (2) Morphology manipulation approaches and models—the ternary blend nanostructure is complex and not trivial to understand. Parallel and alloy nanomorphology models are discussed on the basis of the simultaneous consideration of the intrinsic properties among the involved materials, such as electronic properties and interplay (miscibility) among the host–guest materials. (3) Energy loss management—the addition of donor or acceptor with small energy loss, especially low bandgap material, as the third component holds the promises to reduce the energy loss in ternary OSCs. On the other hand, due to the advantage of the alloyed microstructure in precisely tuning VOC, applying a second donor with deeper HOMO level or a second acceptor with shallower LUMO level is expected to increase VOC and thus reduce the energy loss in ternary OSCs. (4) Stability boosting agent—from the thermodynamic point of view, the stable BHJ microstructure is beneficial and critical in enhancing the OSCs’ long-term thermal and light stability. However, most material combinations suffer from the poor miscibility between the donor phase and acceptor phase, leading to demixing of two phases and thus the performance degradation. On the basis of this concept, rational selection of the third component could facilitate the formation of glassy nanostructure by vitrifying the pure donor phase or acceptor phase. Also it worth noting that suppressed crystallization of the small molecular acceptors by mixing a miscible component is effective to achieve a stable morphology. At the end of the Account, we share our view on the issues that limit the performance of ternary OSCs and outline their perspectives.

Multispectral harvesting rare-earth oxysulphide based highly efficient transparent luminescent solar concentrator

Transparent luminescent solar concentrator (LSC) is extensively regarded as the most promising sunlight tapping device for its application in buildings integrated with photovoltaics (BIPV) or as solar window glass. Conventional LSCs doped with organic dyes suffered from high reabsorption losses with no transparency; whereas, recently reported heavy metal-doped quantum dots avoided such losses but possessed the risk of high toxicity and low ambient stability. Thus, luminophores with massive spectral shifts and cordial relationships with the environment are very much desirable. In this paper, we report the fabrication of PMMA based transparent LSC embedded with nanocrystals of environmental friendiness and multispectral harvesting gadolinium oxysulphide (Gd2O2S:Er,Yb) fluorophore. The Gd2O2S:Er,Yb nanofluorophore absorbs various excitation wavelengths ranging from UV to NIR and emits in the visible region offering huge Stoke's and anti-Stoke's shift concurrently. The non-existent reabsorption losses and overlapping maxima of Gd2O2S:Er,Yb nanofluorophore generated photon flux with solar cells' responsivity enhance the efficiency characteristics of the LSC waveguide. Performance analysis of LSC as a function of varying nanofluorophore dispersion ratio and changing edge width optimizes the fabrication process and exhibits high power conversion efficiency of ∼6.93% and optical efficiency of ∼8.57%. The LSC slab demonstrates high photostability under irradiation for prolonged hours without any dip in the emission characteristics. The Gd2O2S:Er,Yb nanofluorophore diffused LSC waveguide offering spectral tunability, cost-reduction, efficiency enhancement, and high concentration factor whilst being sustainable for long term use makes it a fascinating transparent solar window.

Experimental and theoretical studies of the solid-state performance of electrodeposited Yb2O3/As2Se3 nanocomposite films

The influence of the rare-earth oxide (Yb2O3) on arsenic selenide (As–Se) host is currently investigated and documented in this study. Nanocomposite films were grown using the electrodeposition (ED) technique with the addition of 1 – 4 mol% Yb2O3. The film’s optical structural, optical, morphological, and electronic features were studied. The host matrix presents the monoclinic structure whereas the composite films present two phases –cubic and orthorhombic crystal structure. Crystallites within nano sizes (36.2 nm) were recorded for the pristine film while the composite films showed sizes ranging from 37.2 to 48.1 nm. Moreover, the Raman spectra revealed low energy Raman phonons characteristic of Se8 rings, As4Se4 cages, As–Se hetero-polar bonds whose cleavage was due to the diffusion of the Yb ions into the host matrix as shown by the Raman shift. More so, the refractive index peaked at n = 2.66 in the λ interval of 350–600 nm, while the SEM images showed nano-balls and nanoclusters which are fairly homogeneous. PL studies exhibited multimode emission bands spanning the UV–Vis–NIR regions. First-principles calculations were employed to investigate the structural properties and electronic structure of the pristine (As–Se) film, as well as Yb contribution. It was found that Yb addition leads to reduce the bandgap energy and consequently the lone pair p-states of Se contribute nearby to Fermi energy level. Hence, the experimental and theoretical results of films afford potential applications in phase-change memory (PCM) and downconverting solar cell window layer.

UV‐Selective Optically Transparent Zn(O,S)‐Based Solar Cells

This work reports experimental evidence of a photovoltaic effect in transparent UV‐selective Zn(O,S)‐based heterojunctions. Zn(O,S) has a strong interest for the development of UV‐selective solar cells with high transparency in the visible region, required for the development of nonintrusive building‐integrated photovoltaic (BIPV) elements as transparent solar windows and glass‐based solar façades. By anion alloying, Zn(O,S) mixed crystal absorbers can be fabricated with different sulfur content across the whole compositional range. This allows adjustment of the bandgap of the absorbers in the 2.7–2.9 eV region, maximizing absorption in the UV, while keeping a high level of transparency. Zn(O,S) alloys with composition corresponding to S/(S + O) content ratios of 0.6 are successfully grown by sputtering deposition, and first glass/FTO/NiO/Zn(O,S)/ITO device prototypes are produced. The resulting devices present an average visible transmittance (AVT) of 75% and present photovoltaic effect. By introducing a thin C60 film as electron transport layer (ETL), charge extraction is enhanced, and devices show an efficiency of 0.5% and an AVT > 69%. The transparency of these devices can potentially allow for their ubiquitous installation in glazing systems as part of nonintrusive BIPV elements or to power Internet of Things (IoT) devices and sensors as an integrated transparent component.

Visibly Transparent Solar Windows Based on Colloidal Silicon Quantum Dots and Front-Facing Silicon Photovoltaic Cells.

We demonstrate luminescent solar concentrators (LSCs) based on colloidal silicon quantum dots (SiQDs) as UV-selective fluorophores and coupled with front-facing silicon photovoltaic cells for the solar window application. The visibly transparent LSC composed of a thin layer of liquid SiQD suspension sandwiched between two thin glass slabs constitutes the windowpane, while strips of silicon photovoltaic cells with their front surfaces adhering to the LSC rear surface form the window frame. Furthermore, the LSC perimeter is surrounded by reflecting mirrors for preventing the fluorescence from leaking out through the edges. The SiQDs dispersed in 1-octadecene selectively absorb UV light and re-emit red fluorescence with quantum efficiency about 40%. Owing to the negligible overlap between the absorbance and photoluminescence spectra, the reabsorption effect is insignificant. The front-facing silicon photovoltaic strips located at the window frame can produce electricity by harvesting not only solar radiation but also the SiQD-generated fluorescence propagating from the windowpane. For the SiQD-LSC with the total light absorbing area equal to 12 cm × 12 cm and the reflecting mirrors tilted 45°, an overall power conversion efficiency of 2.47% under simulated sunlight can be obtained of which about 6% is contributed by the SiQD fluorescence. Meanwhile, the SiQD-LSC retains high spectral quality with average visible transmission and color rendering index through the windowpane equal to 86% and 94, respectively.

Chemically Sustainable Large Stokes Shift Derivatives for High-Performance Large-Area Transparent Luminescent Solar Concentrators

Summary Luminescent solar concentrators (LSCs) have recently emerged as valuable candidates for the realization of aesthetically pleasing solar windows for near-zero-energy consumption buildings. The growing demand by the building-integrated photovoltaic sector is urging the development of sustainable production methods that minimize the use of polluting organic solvents and hazardous materials, while still enabling industrial-grade LSCs. Here, we introduce a new class of benzothieno-benzothiophene (BTBT) derivatives as highly efficient reabsorption-free emitters for transparent LSCs featuring high stability and a solvent-free chemical access with sustainability factor as low as 21, 10 to 50 times lower than conventional LSC emitters. By embedding our BTBT emitters in optical-grade polymeric waveguides, we produced large-area (40 cm × 40 cm) LSCs with optical power efficiency as high as 3% (corresponding to an optical quantum efficiency of 54%). These results represent an important advancement toward sustainable solar glazing systems for green architecture.

A numerical study on particle tracking and heat transfer enhancement in a solar cavity receiver

The thermochemical dissociation of natural gas into hydrogen and carbon involves the presence of solid phase carbon particles. In addition to the produced carbon, carbon particles can be seeded to the process as a catalyst which act both as a heat transfer enhancing medium and nucleation site for the dissociation reaction. However, presence of discrete phase particles imposes various challenges such as deposition on solar reactor walls and windows, and clogging of the exhaust. Meticulous reactor-receiver design optimization is therefore required and is presented in this study. The Discrete Phase Model (DPM) was implemented in a numerical CFD model to track injected carbon particles in a Lagrangian framework. Validation of the model was done with respect to available experimental data and showed similar deposition phenomena on the reactor window. A parametric design study was performed taking into account flow rates, particle size, particle loading and receiver geometry. Use of a finer particle size distribution demonstrated the ability of the flow to entrain more particles to the exhaust and reduce deposition on the bottom wall of the cavity. Three design iterations on an existing 1 kW solar cavity receiver were proposed, depicting an increase of at least 6.5% on the outlet gas temperature and 4% on the overall average gas temperature within the receiver. Results of this study highlighted the importance of flow configuration, flow parameters and particle size on the deposition and heat transfer inside solar cavity receivers. Outcome of this study can serve as a reference for solar reactor design involving presence of particulate media.

Protecting superhydrophobic surfaces

Superhydrophobic coatings that make water droplets bounce off, taking dust and debris with them, could lead to self-cleaning solar panels, windows, and cars. But these coatings are not durable, whi...

Shades of transparency

Dye-sensitized solar cells are promising as power-generating solar windows yet their fixed transparency prevents control of indoor lighting and temperature. Researchers now present a device that dynamically self-adjusts its optical transmittance with sunlight intensity, opening up a way to energy-efficient self-powered building facades.

α-CsPbBr3 Perovskite Quantum Dots for Application in Semitransparent Photovoltaics.

As effective light absorbers in solar cells, CsPbI3 all-inorganic perovskite quantum dots (QDs) have received increasing attention, benefitting from their suitable optical band gap and thermal stability. However, the easy cubic to yellow orthorhombic phase transition hinders their further application in stable photovoltaic devices. CsPbBr3 QDs have been targeted as a promising material for ultrahigh voltage and stable solar cells. In this work, we first develop a simple yet efficient post-treatment method using guanidinium thiocyanate (GASCN), which is able to exchange the native capping ligands of CsPbBr3 QDs, thus improving the carrier transport properties through enhanced electrical coupling between QDs. Additionally, the morphology and crystalline properties of solid QD films are also improved. Therefore, simultaneously improved open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF) were obtained in the corresponding CsPbBr3 QD devices. Finally, the QD solar cells based on optimal hole-transporting layers delivered the highest efficiency exceeding 5% together with an ultrahigh Voc of 1.65 V, representing the most efficient CsPbBr3 QD solar cells to date. More importantly, the CsPbBr3 perovskite QD solar cells developed here exhibit excellent stability, ultrahigh voltage, and high transparency over the entire visible spectrum region, demonstrating their great potential in applications like solar windows of greenhouse and hydrogen generation driven by perovskite solar cells.

An experimental work on the impact of new combinations of solar chimney, photovoltaic and geothermal air tube on building cooling and ventilation

Renewable energy applications play a major role in covering the energy demand for building cooling and ventilation. In this paper, an experimental investigation is performed on cooling and ventilation of a building room locating in New Borge Alarb city, Alexandria, Egypt by new combination of solar chimney and geothermal air tube heat exchanger system. PV panel is installed by new technique at the chimney back to produce power and its performance is compared to an identical PV outside the room. The study is performed for the chimney and PVs facing south of an angle with the horizontal 30° and 45° and for natural and forced airflow inside the geothermal tube. The geothermal tube and chimney ventilation systems are compared with the natural ventilation system of the solar chimney and window. The results indicate that the proposed systems prove their ability to cool the room temperature up to 3.5 °C and change daily its air 42 times. Minimum ventilated air occurs at natural geothermal tube-chimney system of angle 30°. The ratio of the total daily ventilated air by natural geothermal tube-chimney to that by chimney-window is about 56.3% and 65% at 30° and 45°, respectively and for heat released is 55.6% and 64%, respectively. Maximum daily heat released from the room is achieved at chimney inclination angle 45° for natural geothermal tube-chimney-PV system. Maximum PV output power inside the chimney represents 70% of the maximum PV output power outside the chimney which is 120 W/m2 at chimney inclination angle 30°.

Experimental study on the performance of solar window films in office buildings in Kuwait

This work examines the solar performance of double-glazed windows in four offices in ACK buildings with and without solar window film in actual working conditions. Window films are passive thin films stick to the interior or exterior of windows to effect various solar-optical impacts including energy saving, UV reduction, and increased thermal comfort. For this study, the 3M Neutral 20 and 70 are selected which are made of multilayer nanofilms of 220 SAN25/THV 95-nm thick reflective layers. Real-time measurements of temperature, humidity, and luminous were conducted in 5 min intervals over the months of June, July, and August 2019 and data stored through WiFi system in iClouds. Arduino-type microprocessors and various temperature-humidity, and LUX sensors were assembled and programmed to transfer and store data in real time. Exploring and analyzing the data collected for four offices with and without window films in summer of Kuwait, it is evident that window film has good potential to save water by preserving interior humidity to the level of human comfort, decrease interior temperature to save energy and reduce CO2 footprints, to restrict the solar UV rays to minimum level, and to reduce visual impacts of high solar luminous. The benefits and drawbacks of the selected window films are discussed here for the weather condition of Kuwait.

Bright Silicon Nanocrystals from a Liquid Precursor: Quasi-Direct Recombination with High Quantum Yield.

Silicon nanocrystals (SiNCs) with bright bandgap photoluminescence (PL) are of current interest for a range of potential applications, from solar windows to biomedical contrast agents. Here, we use the liquid precursor cyclohexasilane (Si6H12) for the plasma synthesis of colloidal SiNCs with exemplary core emission. Through size separation executed in an oxygen-shielded environment, we achieve PL quantum yields (QYs) approaching 70% while exposing intrinsic constraints on efficient core emission from smaller SiNCs. Time-resolved PL spectra of these fractions in response to femtosecond pulsed excitation reveal a zero-phonon radiative channel that anticorrelates with QY, which we model using advanced computational methods applied to a 2 nm SiNC. Our results offer additional insight into the photophysical interplay of the nanocrystal surface, quasi-direct recombination, and efficient SiNC core PL.

Doublet-waveplate polarization transceiver system for backscattering suppression in laser communication terminal

The backscattering suppression capability of the optical signal transceiver is the key to establish a single wavelength full-duplex bidirectional laser communication link. When the signal is transmitted and received through the same telescope of the laser communication terminals, stray light from the high-power laser on mirrors will be received by the high-sensitivity detector, affecting the sensitivity of the system. In this paper, the polarization modulation characteristics of scattered light by the mirrors with different roughness are analyzed. The traditional system based on polarization splitting and transmitting with a single quarter waveplate is improved by using a doublet waveplate, i.e., a combination of a half waveplate and a quarter waveplate. The transceiver system including the off-axis optical antenna is developed and the signal transceiver isolation (ability of suppressing backscattering light) is improved by 7∼8 dB. Although the system complexity is increased, the waveplate can work as a solar window to improve the environmental adaptability. The laser communication terminal would meet the requirements of further link communication, including inter-satellite networks under the same aperture condition.

System for manufacturing complete Cu(In,Ga)Se2 solar cells in situ under vacuum

We present the development of a small foot-print physical vapor deposition (PVD) system for in-situ deposition of all layers required in a complete Cu(In,Ga)Se2 (CIGS) solar cell. Seven sputtering magnetrons and one valved-cracker source have been custom designed and manufactured for this system, named SpuTtering for Advanced Research (STAR). The purpose of STAR is to develop a technique to fabricate a complete CIGS solar cell, including contacts, absorber, buffer, and window layers, under high vacuum with the aim to transfer this technology to a future industrial production line. The system’s capabilities and its relatively high throughput place it somewhere in between research and industrial development levels. It is possible to work on the deposition of the back contact, the CIGS absorber, and the window layer of three solar cells simultaneously. Calibration data, selection of parameters for the deposition of the individual layers, and initial results of a complete CIGS solar cell developed with STAR are reported.

Synthesis and technical analysis of 6-butyl-3-[(4-chlorophenyl)diazenyl]-4-hydroxy-2H-pyrano[3,2-c] quinoline-2,5(6H)-dione as a new organic semiconductor: Structural, optical and electronic properties

A novel 6-butyl-3-[(4-chlorophenyl)diazenyl]-4-hydroxy-2H-pyrano[3,2-c] quinoline-2,5(6H)-dione (dye 2) was effectively synthesized. The structure of (dye 2) has been set up using its accurate spectral and elemental analysis statistics. X-ray diffraction (XRD) analysis exhibited that (dye 2) has a polycrystalline nature. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were utilized. Optical parameters, as well as absorption index of (dye 2), were calculated using diffused reflectance wavelength measurements range 200–2300 nm. The bandgap in optics was determined by applying the Kubelka–Munk theory. Two optical band gap values (2.57 and 2.33 eV) were obtained. The first value (2.57 eV) is responsible for the direct transition while the other value (2.33 eV) is responsible for the indirect bandgap. AC fields were primarily utilized to calculate and interpret both AC electrical conductivity, the dielectric constant, and the dielectric loss. Finally (dye 2) turns out to be efficiently material and may act as a novel solar cell window due to its high bandgap.

Role of refractive index in highly efficient laminated luminescent solar concentrators

As a large-area solar radiation collector, luminescent solar concentrators (LSCs) can be used as power generation units in semitransparent solar windows, modernized agricultural greenhouses and building facades. However, the external optical efficiency and long-term stability of the LSCs limit their practical applications due to the sensitivity of the emitters to the light and environmental conditions. Here, we used the concept of “laminated glass” to prepare LSCs, which consist of two waveguide layers and the quantum dots (QDs)/polymer interlayer, and we tune the refractive index of the different parts of the system to improve the external optical efficiency and stability of the LSCs, simultaneously. The waveguide layer can be glass, quartz, polymethyl methacrylate (PMMA) and other transparent materials. The CdSe/CdS core/shell QDs were used as fluorophores to prepare the interlayer of the LSCs. The external optical efficiency of the laminated LSCs is associated with the refractive index of the three layers: the closer the refractive index, the higher the ηopt. The highest external optical efficiency of 3.4% has been achieved for the laminated PMMA/QDs-polymer/PMMA LSCs, which improved ~92% compared to the single-layered CdSe/CdS based LSCs. To the best of our knowledge, this is the highest efficiency for the LSCs based on CdSe/CdS QDs. These results pave the way to realize high efficiency laminated windows as power generation units by suitably tuning the structure of the LSC, and provide the theoretical guidance for the LSCs utilized in building integrated photovoltaics.

Semi-transparent Schottky junction solar cell based on evaporated CdSe thin films: Influence of post-deposition air-annealing

FTO/CdSe/Al semi-transparent Schottky junction solar cells were fabricated by evaporating 300 nm CdSe thin films onto the FTO electrode and forming the Schottky junction by evaporation the aluminum onto the absorber layer. The performance of the samples was optimized by air-annealing the absorber layer prior to the evaporating of the top electrode. Also, the structural, optical and electrical properties of thermally evaporated CdSe thin films were investigated as a function of post-deposition air-annealing temperature. The surface morphology of the specimens was studied using field emission scanning electron microscope (FE-SEM) analysis. X-ray diffraction (XRD) analysis revealed the hexagonal structure of the samples. The crystallite size, micro-strain and dislocation density of CdSe thin films were evaluated using XRD patterns. The transmittance spectra in the wavelength range of 400−2500 nm were measured and then used to study other optical parameters. The optical energy band gap was decreased with air-annealing from 2.17 eV to 1.69 eV. It is observed that complex refractive index, relative density, complex dielectric constant and electrical polarizability of specimens were increased by air-annealing. Electrical conductivity and the photovoltaic efficiency of FTO/CdSe/Al Schottky barrier devices were improved by thermal annealing and annealed sample at 300 °C shows the best performance (η = 1.53 %). Obtained results show that CdSe thin films are a promising candidate to use as an absorber layer in semi-transparent solar cells and colorful photovoltaic windows.