High Visible Transmittance Research Articles

Design and demonstration of a simple, low-cost transparent solar absorber for glass window applications

Windows are a major source of heat loss from buildings in cold climates. Developing coatings for windows that retain high visible transparency and strongly absorbs solar energy in the near infrared region can help reduce energy consumption and cost for indoor heating. Nanophotonic structures based on metasurface and metamaterials have shown great potential for such applications. Unfortunately, most of the designs proposed so far are difficult to fabricate or expensive. In this work, we report the experimental demonstration of a low-cost alternative based on Ni/SiO2/Ni multilayer structure. The device provides a large increase in temperature under solar illumination while retaining high visible transmission. Our optical and thermal measurements reveal that the performance of the device remains stable over a long period. The combination of low cost, ease of fabrication, good optical and thermal performance, and long-term stability makes it a promising design for passive heating of windows in cold climates.

Polyvinyl Butyral Solid Electrolyte Film and Its Electrochromic Laminated Safety Glass.

In recent years, the application of electrochromic laminated safety glass has attracted more and more attention, relying on polyvinyl butyral (PVB) solid electrolyte film. Herein, the ionic conductivity (σ) of the PVB film has been improved by a cross-linked structure and blended with LiClO4, which can reach as high as 1.78 × 10-4 S cm-1 at room temperature. In addition, their excellent comprehensive characteristics have been confirmed, such as mechanical strength, high visible light transmittance (>90%), high bond strength (4.2 MPa), and excellent thermal stability. Based on the PVB film above, WO3-laminated electrochromic devices with 5 × 5 cm2 and 10 × 10 cm2 areas are constructed. They can remain stable after 20 000 cycles monitored by cyclic voltammetry curves, indicating the PVB solid polymer electrolyte (PSPE) with a cross-linked structure has the potential commercial viability of large-area electrochromic devices (ECDs).

Optimizing Na2EDTA Concentration for Enhanced Properties of SILAR - Deposited CTS Thin Films

Abstract This study investigates the impact of varying Na2EDTA concentrations on the properties of copper tin sulfide (CTS) thin films deposited on soda lime glass substrates using the successive ionic layer adsorption and reaction (SILAR) method. The aim is to optimize CTS thin film growth for photovoltaic technology applications. CTS thin films were prepared using SILAR with Na2EDTA concentrations of 0.01M, 0.04M, and 0.07M, resulting in samples CTS01, CTS04, and CTS07. Characterization techniques included XRD, SEM, EDAX, FTIR, I-V curves, transmittance spectra, and Tauc plots. The results reveal significant variations in film properties with changing Na2EDTA concentration. XRD patterns indicate polycrystalline films with an orthorhombic CTS phase. SEM images show smooth, dense films with localized clusters. FTIR spectra detect hydrocarbon chains, aromatic rings, and hydroxyl or ether groups. The I-V curves of three samples (CTS01, CTS04, and CTS07) show a voltage-dependent transition from semiconducting to ohmic behavior. The CTS01 exhibits superior conductivity (3.13x10-5/Ωm), while the samples' resistance and conductivity values show an inverse relationship. Transmittance curves display low UV transmittance and high visible transmittance,suggests that the samples are highly absorptive in the UV range and become more transparent in the visible range, indicating potential applications in optical filtering and photovoltaic devices. Tauc plots estimate band gap energies of 3.66, 3.89, and 3.23 eV, indicating high band gap energies suitable for buffer layers in solar cells. The correlation between band gap energy and crystallite size as a function of Na2EDTA concentration is also observed. The study demonstrates the importance of optimizing Na2EDTA concentration for achieving high-quality CTS thin films with desirable properties for photovoltaic applications. The findings highlight the potential of CTS thin films for solar cells, optical filtering, and photonic devices.

Construction of epoxy resin with enhanced flame retardancy, mechanical properties, and satisfactory transparency based on a novel bi‐DOPO and hydrogen‐bonding network

AbstractEstablishment of high‐performance epoxy resin with satisfactory fire safety, mechanical properties, and excellent transparency is urgently desirable, but still remains significant challenges. Herein, a super‐tough yet high flame retardant epoxy resin (EP/BTD) was designed and prepared by incorporating bi‐DOPO structure and hydrogen‐bonding networks. Although the phosphorus content was only 0.69 wt% (10 wt% of bi‐DOPO flame retardant [BTD]), EP/BTD‐10 showed a high limiting oxygen index value (33.4%), satisfactory UL‐94 rating (V‐0), and good heat suppression ability (total heat release [THR] and peak heat release rate [PHRR] reduced to 29.0% and 42.2%, respectively). Furthermore, the flame retardant mechanism of EP/BTD was illustrated and attributed to dual‐phase fire‐retardant effect. Additionally, EP/BTD‐7.5 featured notably mechanical properties, of which the tensile strength, elongation at break and impact strength increased by 44.6%, 40.0%, and 232.6%, respectively, due to hydrogen‐bonding network and π–π interaction. More importantly, EP/BTD maintained high visible light transmittance and excellent UV‐blocking properties. In summary, this work provided a guidance for the development of high‐performance epoxy resin and was expected to expand the practical applications.

Preparation and Characterization of Nanostructured ITO Thin Films by Spray Pyrolysis Technique: Dependence on Annealing Temperature

Transparent conducting oxides (TCOs) like Indium tin oxide (ITO) have wide attention from all scientists which have low resistance and high visible light transmittance, used as transparent electrodes in many optoelectronic devices such as liquid crystal displays, touch screens, light emitting diodes, and solar cells. In this research, the relationship between the crystallization, optical transmittance, and surface roughness of nanostructured ITO thin films and the change in annealing temperature was investigated. To enhance the efficiency of this material in optoelectronic applications, both the optical transmittance in the visible region and the crystallite size must be increased. These results can be obtained by the heat treatment of the films. Nanostructured ITO thin layer films have been successfully prepared at a substrate temperature equal to (350)℃ by chemical spray pyrolysis (CSP) technique. The physical characterizations of nanostructured ITO thin layer films were investigated at different annealing temperatures (400,450 and 500)℃. The presence of diffraction peaks indicates that the as-deposited and post annealed films are polycrystalline cubic structure and the peak (400) is a preferred growth orientation. For all samples the value of intensity of diffraction peaks increases with increasing substrate temperature. The crystallite size of nanostructured ITO thin films is strongly related to the annealing temperature. The crystallite size estimated from XRD was found to rise with rising annealing temperature. The surface roughness of nanostructured ITO thin layer films increases with rising annealing temperature. High values of transmittance have been measured in the visible region 550 nm equal to (70, 82, 84 and 88)% corresponding to annealing temperature (350,400,450 and 500)℃ respectively.

Selective Void Deposition by Continuous, Ultrathin Ag Film Enabled Stable, High-Performance AgNWs-Based Transparent Heaters.

Metallic nanowire-based transparent conductors (MNTCs) are essential to various technologies, including displays, heat-regulating windows, and photo-communication. Hybrid configurations are primarily adopted to design stable, high-functioning MNTCs. Although hybrid MNTCs enhance electrical performance, they often suffer from optical degradation due to losses associated with the hybrid layers. Highly conductive hybrid MNTCs with minimal reduction in transparency are achieved with AgNWs/Ag(O)/Al-doped ZnO (AZO) design. The design provides a high visible light transmittance of 95.1%, representing a minimized optical loss of 3% compared to pristine AgNWs by optimizing optical interference between the AZO and Ag(O) layers. Furthermore, it allows for enhanced mobility of metallic nanowires by controlling the selective formation of conductive layers in the voids of the nanowire networks. The oxygen additive enables a continuous Ag ultrathin film of 6nm in the macro-voids of AgNWs system, corresponding to 25 times higher mobility for AgNWs/Ag(O)/AZO than that of sole AgNWs. The significant enhancement in the mobility of AgNWs/Ag(O)/AZO induces a reduction of sheet resistance of MNTCs by 73%. The AgNWs/Ag(O)/AZO, with an optimized sheet resistance of 24 Ω sq-1, is explored for transparent heater applications, demonstrating a fast thermal response with reliable stability, as evidenced by consistent high-temperature profiles during prolonged operation.

Amorphous In–Al–Sn–O Thin Film Transistors and Their Application in Optoelectronic Artificial Synapses

AbstractIn‐Al‐Sn‐O (IATO) is a very promising novel amorphous oxide as the active layer of thin film transistors (TFTs). Herein, IATO TFTs are first fabricated with the effects of annealing on IATO films and TFTs being studied. The IATO films possessed amorphous structure, flat surface morphology, high visible light transmittance, and wide optical bandgap ≈4.20 eV before and after annealing even at 400 °C. The minimal surface roughness and internal defects are obtained for the 300 °C annealed IATO film. Correspondingly, the 300 °C annealed TFTs demonstrated the best overall performance including high saturation mobility (8.55 ± 0.62 cm2 V−1 s−1), low subthreshold swing (0.40 ± 0.07 V dec−1), ideal on/off current ratio (1.25 ± 0.09 × 108), and negligible hysteresis (0.23 ± 0.03 V) values. The 300 °C annealed TFTs are then applied in optoelectronic artificial synapses and exhibit typical synaptic properties, including excitatory postsynaptic current, paired‐pulse facilitation, and short‐term plasticity to long‐term plasticity conversion in response to light stimulation. The international Morse code and repetitive learning‐forgetting behavior of the human brain are also successfully simulated. In particular, an emotion‐memory efficiency model is proposed and the emotion effect on human memory efficiency is successfully imitated via the regulation of gate voltage.

Bidirectional Temperature‐Responsive Thermochromic Hydrogels With Adjustable Light Transmission Interval for Smart Windows

AbstractThermochromic smart windows have been widely developed for solar regulation to save building energy. However, most current smart windows still exhibit a single responsiveness to a specific temperature, which is not conducive to daytime energy saving or nighttime privacy protection. Herein, a low‐temperature response is achieved by pre‐initiation of the monomer acrylamide (AAm) and acrylic acid (AA) in the synthesis of P(AAm‐co‐AA). Then, N‐isopropyl acrylamide and AAm are introduced into P(AAm‐co‐AA) to form a pre‐polymerized precursor solution. The liquid precursor solution can be encapsulated within two quartz glasses and synthesized in situ to prepare smart windows, which exhibit a high visible light transmittance of 84.4%, excellent solar modulation of 69.5%, and bidirectional temperature responsiveness (cold and hot). In addition, the upper critical solution temperature and the lower critical solution temperature of the hydrogel and the light transmission interval between the two temperatures can be flexibly adjusted to adapt to different climates and individual user needs. The designed smart window maintains a high light transmission within the human body's comfort temperature range. The bidirectional temperature response window achieves the dual functions of energy saving and privacy protection, making it an ideal smart window candidate with good prospects for practical applications.

A Study of the Optical Properties and Stability of Cs0.33WO3 with Different Particle Sizes for Energy-Efficient Window Films in Building Glazing

Cs0.33WO3 (CWO) is a widely used inorganic material in window films and glass coatings, known for its excellent near-infrared radiation (NIR) blocking property and high visible light transmittance (Tvis). However, the stability of NIR blocking and the optical properties of CWO in the process of application is an urgent and important problem, because significant changes in optical results can impact the related products, such as window films, glass coatings, and so on. In this paper, the particle sizes and optical properties of CWO are tested to study the light stability and their relative relations. The results indicate that CWO particle sizes between 130 nm and 100 nm (D90, the point where 90% of the particles have a diameter smaller than the specified value) exhibit high stability in terms of NIR blocking and visible light transmittance (Tvis). CWO particles with D90 < 100 nm experience a greater reduction in NIR blocking, though this ability significantly recovers upon exposure to sunlight, making these coatings particularly suitable for use in tropical and subtropical climates.

Multilayer thin film mid-infrared broadband absorber with high visible light transmittance

Few reports on absorbers achieve both high transmittance of visible light and strong absorption of mid-infrared light. Here a multilayered absorber with high visible light transmittance and strong broadband absorption in the mid-infrared band is proposed. The absorber is four-layer films of ITO/SiO2/ITO/SiO2 successively deposited on single-sided conductive glass by electron beam evaporation technology. The experiment shows that the integral transmittance in the 400–800 nm range is 82.8 %, and the integral absorption in the 3–5 μm band is 88.2 %.

Signal Components and Impedance Spectroscopy of Potential p‐Si/n‐CdS/ALD‐ZnO Solar Cells: EIS and SCAPS‐1D Treatments

AbstractA silicon heterojunction (SHJ) solar cell with the attractive and widely used atomic layer deposited (ALD)‐ZnO/n‐CdS/p‐Si configuration is examined in this work to learn more about its electrical properties. Using EIS and SCAPS‐1D, a comprehensive model of the device is created and then simulated. Theoretical aspects of the cell are examined through the use of similar electrical circuit models, focusing on the transmittance spectrum made possible by the ALD‐ZnO layer's low reflectance and high visible transmittance. In this study, the C–V tool is used to study the trap states in the silicon absorber layer under different lighting conditions and wavelengths. The doping concentration and built‐in potential are determined using the Mott–Schottky technique. In addition, the cell's properties are investigated by measuring its G–V, G–F, C–T, and C–F in different real‐world scenarios. As a means of visualizing the electrochemical impedance data, Nyquist plots—sometimes called Cole–Cole plots—are utilized. By utilizing absolute impedance and phase shifts, Bode plots are employed to examine the system's frequency response. Last, the results of the SHJ cell's spectral response measurements are given, which confirm the results of the Nyquist plots.

Tough, high-strength, flame-retardant and recyclable polyurethane elastomers based on dynamic borate acid esters

With the wide application of polyurethane elastomers, it is necessary to develop recyclable, fire-retardant polyurethane elastomers with great mechanical properties to comply with industrial requirements. Herein, we fabricated a flame-retardant, recyclable, strong yet tough polyurethane elastomer (PIDB-1) based on dynamic borate acid esters. The introduction of phosphaphenanthrene and boron-containing groups endow PIDB-1 with great flame retardancy, as reflected by it achieving the vertical burning (UL-94) V-0 rating. The PIDB-1 film shows high visible light transmittance, and its transmittance reaches 90 % at the wavelength of 800 to 900 nm. The tensile strength of PIDB-1 is 54.9 MPa, and its toughness reaches 207.8 kJ/m3, indicative of superior mechanical properties. Meanwhile, the dynamic borate acid esters allow the PIDB-1 elastomer to possess physical and chemical recyclability. When using PIDB-1 as a polymer matrix for carbon fiber-reinforced polymer composites, the carbon fibers can be fully recycled. This work provides an integrated design strategy for creating transparent, flame-retardant, recyclable polyurethane elastomers combining high strength and toughness based on dynamic borate ester bonds, which is expected to find wide applications in different industries.

CsxWO3 films with excellent infrared shielding ability and high visible light transmittance prepared via magnetron sputtering

Caesium tungsten bronze materials are widely used in various applications, such as architectural glass, medicine, insulation coating and textile fibre, owing to their excellent mechanical, optical and thermal properties. In this study, a caesium tungsten bronze (CsxWO3, x = 0.3–0.32) target with a relative density of 99.63 % and uniform microstructure was successfully prepared via hot-pressing sintering. CsxWO3 films were deposited on a quartz glass substrate via magnetron sputtering, and the mechanisms and effects of the substrate temperature and oxygen flow rate on the phase structure, microstructure and optical properties of CsxWO3 films were investigated. When the substrate temperature increased, the crystallinity and oxygen vacancy concentration of the CsxWO3 film improved. Consequently, the visible light transmittance of the film decreased, whereas the infrared blocking rate considerably increased, reaching up to 93.877 %. With the increase in the oxygen flow rate, the visible light transmittance exhibited an increasing trend, reaching a maximum value of 84.319 %, whereas the infrared blocking rate remained relatively stable. We successfully fabricated CsxWO3 films possessing a visible light transmittance of 66 % and infrared blocking rate of 94.97 % under the conditions of a substrate temperature of 300 °C and an oxygen flow rate of 2.5 sccm. Our study offers a method for the large-scale production of CsxWO3 films, which are excellent infrared shielding materials, rendering a substantial contribution to global energy conservation and emission reduction.

Low-temperature synthesis and luminescence properties of blue-emitting β-SiAlON:Eu2+ phosphor using melamine as a self-propagating raw material

Sialons are widely recognized for their rigid lattice structure, high visible light transmittance, and excellent thermal stability, making them suitable matrix materials for activators. In this paper, we successfully prepared β-sialon phosphors, β-Si6-zAlzOzN8-z:Eu2+ (β-SiAlON:Eu2+), using an organic precursor method at a low synthesis temperature for the first time. X-ray diffraction analysis and Rietveld refinement confirm the β-SiAlON:Eu2+ phosphor possesses a hexagonal structure with a P63 space group. Under 320 nm excitation, β-SiAlON:Eu2+ phosphor exhibits a blue emission band centered at 415 nm due to the 5d → 4 f electron transition of Eu2+, which differs significantly from other β-SiAlON:Eu2+ phosphors with green emission. It is interesting that excessive Eu2+ activators make β-SiAlON:Eu2+ phosphor possess a green emission band centered at 510 nm. Therefore, the light-emitting color of β-SiAlON:Eu2+ phosphor shifts from the blue to the green with the increase of Eu2+ concentration. Furthermore, the activation energy of β-SiAlON:0.02Eu2+ sample is calculated to be about 0.2527 eV, which confirms β-SiAlON:Eu2+ phosphor has good thermal stability. The article presents a low-temperature and cost-effective synthesis method for preparing sialons, as well as a novel blue β-SiAlON phosphor for solid-state lighting.

Realization of high performance optical power limiting (OPL) materials by introducing OPL-active metal alkynyl segments into side chains of Pt(II) polyynes

To date, it is still a great challenge to realize high optical power limiting (OPL) ability with excellent visible light transmittance at the same time for organic OPL materials. For example, the carbazole-based Pt(II) polyynes usually showed good visible light transmittance but weak OPL ability. In this work, we designed and synthesized two high performance OPL materials by introducing OPL-active metal alkynyl segments into the side chain of carbazole-based Pt(II) polyynes for the first time. Arranging metal alkynyl in side chains could effectively disrupt the π-conjugation between the polymer backbones and side chains, thus the developed polymers showed excellent visible light transmittance. In addition, with more OPL-active metal alkynyl groups in the side chain, the developed polymers were expected to show good OPL performance at the same time. To further improve the OPL performance, we utilized the triphenylamine and triarylboron groups to manipulate the involvement of the Pt(II) center in transition processes, which could effectively influence the intersystem crossing to enhance the population of triplet states. As a result, the Pt(II) polyyne CzTPA with the triphenylamine group linked to OPL-active metal alkynyl groups in side chains displayed the best OPL performance with the figure of merit σex/σo of up to 7.17, which was much higher than that of state-of-the-art OPL material C60. Therefore, this work demonstrates a promising strategy to develop high performance OPL materials possessing both strong OPL ability and impressively high visible light transmittance at the same time.

Preparation of low thermal expansion, transparent LAS glass-ceramics via simplified heat-treatment method

Li2O–Al2O3–SiO2 (LAS) glass-ceramics are commercially significant due to their unique microstructure and exceptional properties, including near-zero thermal expansion coefficient, making them suitable for a wide range of applications. However, the content of SiO2 and Al2O3 in the composition of LAS glass is very high, which leads to high viscosity and very difficult melting of this type of glasses. In order to reduce the melting temperature of the glass, use of relatively high Na2O in the basic glass composition allows high-quality glass to melt. Employing a simplified heat-treatment method, LAS glass-ceramics are prepared with Australian spodumene as the primary material. By exploring the effect of crystallization temperature on the structures and properties of the resulting LAS glass-ceramics, samples with excellent comprehensive properties are achieved. The prepared glass-ceramics are thoroughly characterized using DSC, XRD, FTIR, SEM, and TEM, along with assessments of their viscosity, thermal, optical, and mechanical properties. Relatively more Na2O is introduced into the glass compositions, which can lower the melting temperature of the glass to below 1600 °C. The basic glass is annealed at 700 °C for 2 h, nucleation phenomenon Nucleation phenomenon can be generated in the LAS glasses. When the microcrystalline temperature of glasses increases from 835 °C to 910 °C, the main crystalline phase of glass-ceramics changes from β-quartz solid solution to β-spodumene solid solution. The change in the main crystal phase has significantly affected the properties of glass-ceramics. When the crystallization temperature is below 860 °C, the glass-ceramics exhibit a low negative expansion coefficient (<-0.5 × 10−6 K−1), high visible light transmittance (>85 %), and excellent average flexural strength (173.3 MPa).

Fabrication of a hot mirror using ITO-free electrochromic films

In this study, WO3/Ag/W/WO3 (WAWW) films were deposited at room temperature on a B270 glass substrate from W and Ag targets using a radiofrequency magnetron reactive sputtering system. The influence of the thin tungsten interlayer on the electrical and optical properties of the WAWW layer structure was investigated through ellipsometry, a four-point probe and a spectrophotometer. It was determined that the thin tungsten interlayer effectively prevented the oxidation of the silver film. The WAWW film had a dielectric-metal-dielectric (DMD) layered structure with good electrical conductivity and high visible transmittance. The tungsten layer was no more than 2-nm thick. The sheet resistance and luminous transmittance of the WO3(29.5 nm)/Ag(14.2 nm)/W(2 nm)/WO3(68.6 nm) film were 4.64 Ω/sq and 65.4 %, respectively. Based on the WAWW four-layer structure, stacked WO3(29.5 nm)/Ag(14.2 nm)/W(2 nm)/WO3(68.6 nm)/Ag(16.9 nm)/W(2 nm)/WO3(30.4 nm) seven-layer structures deposited on B270 glass substrates were used for both ITO-free electrochromic and hot mirror applications. The visible (400–700 nm) and NIR (700–1200 nm) transmittance values of the bleached WAWW seven-layer structure were 71.5 % and 9.9 %, respectively. The visible transmittance of the colored WAWW seven-layer structure was 23.6 %. Finally, the bi-layer WAWW films were used to obtain an ITO-free WAWW seven-layer structure with a good electrochromic and optical performance.

The electronic structure, optical property and n-type conductivity for W-doped α-Ga2O3: hybrid functional study

Based on the hybrid functional method, the electronic structure, optical property and electron effective mass of α-Ga2O3, together with the properties for intrinsic and extrinsic defects incorporated into α-Ga2O3 are studied. Obtained results indicate the α-Ga2O3 possesses a wide band gap (5.31 eV), small electron effective mass (0.22 m0) and a high visible light transmittance. The nonstoichiometric α-Ga2O3 is not an excellent n-type semiconductor. To improve the n-type conductivity, the W-doped α-Ga2O3 is studied. We find that W Ga is a promising n-type defect due to its relatively small ionization energy ϵ(0/+) (0.30 eV). When the equilibrium fabrication method is selected, the WO2 is a promising dopant source. Using the equilibrium fabrication method, the defect complex (V O+ W Ga) would be formed, and the ionization energy ϵ(0/+) for defect complex (V O + W Ga) would decrease to 0.08 eV, which implies that a great number of free electrons could be induced in the samples. We expect that this work can promote the understanding of the n-type conductivity for α-Ga2O3 and provide significant insights for the development of a transparent n-type semiconductor.

In-situ growth of Cs0·33WO3@ATO composite material with enhanced NIR shielding rate for energy-saving coating

Driven by the global goal of “carbon neutrality”, energy conservation, emission reduction and low-carbon development have become important research directions. Transparent thermal insulation materials can effectively shield near-infrared radiation while maintaining high visible light transmittance, making them widely applicable in building energy conservation. In this paper, antimony-doped tin oxide (ATO) and cesium tungsten bronze (CsxWO3, or CWO) are chosen to be composited in order to solve the problems of the poor shielding effect of ATO for short-wavelength near-infrared (NIR) light and the unsatisfactory shielding effect of CWO for long-wavelength NIR light. Therefore, in this study, we employed a one-step hydrothermal method to form a novel CWO@ATO core-shell structure to combine the advantages of both ATO and CWO. By adjusting the composite ratio of ATO and CWO, both the physical and electronic stucutres are effectively tuned to promote the optical modulation in a broad bandwidth. Enventually, the core-shell structured composite exhibit an excellent near-infrared blocking property, surpassing the pure ATO by 27.8 % in the wavelength region of 780∼1500 nm while improving by 14.9 % compared to CWO in the long wavelength between 1500 and 2500 nm. Furthermore, the prepared CWO@ATO core-shell structure repesents near-infrared shielding rate as high as 93.1 % in the full NIR spectrum, and possesses an overall thermal insulation coefficiency (THI) of 9.33 in the full range from 780 nm to 2500 nm, which is substantially larger than that of pure ATO and CWO by a factor of 2.37 and 3.05, respectively. This core-shell structure engineering realizes the utilization of complementary advantages of ATO and Cs0·33WO3 materials, providing a new method to improve the near-infrared performance of energy-saving glass coating, and having broad application prospects in the field of low-carbon buildings.

Hierarchical self-constructed molecular layers of small bifunctional molecules with strong molecular dipole moments for improvement of quantum efficiency in inorganic quantum dots

Hierarchically structured self-assembled molecular layers are functionally versatile and structurally tunable, which are nanoscale molecular building blocks with a wide range of applications from biosensing systems to optoelectronic devices. Herein, we present a facile and effective strategy to fabricate hierarchical self-constructed molecular layers comprising small bifunctional molecules with strong molecular dipole moments for improvement of quantum efficiency in inorganic quantum dots (QDs) by using the cooperative interfacial self-assembly of hydrophilic bifunctional molecules on the polar electrode surface. The spontaneous construction of nanostructured molecular layers with different molecular dipole moments was simply achieved through solution-dipping and in situ interfacial self-organization of 3-mercaptopropionic acid or 1-propanethiol molecules on the surface of indium tin oxide (ITO) anode. It is experimentally revealed that these functional molecules formed uniform and ultrathin self-constructed molecular nanolayers on the ITO surface via covalent bonding, where bifunctional 3-mercaptopropionic acid molecules induced a polar molecular surface of thiol groups with strong dipole moments, whereas 1-propanethiol molecules formed a relatively hydrophobic surface of short alkyl chains with weak dipole moments. In addition, the nanoscale ultrathin nature of these molecular layers afforded high visible light transmittance comparable to that of pristine ITO substrate. The electro-optical properties of the QD cells revealed that hierarchical self-constructed molecular nanolayer with strong molecular dipole moments exhibited superior current and luminescent properties with a 162% improvement in external quantum efficiency relative to those of a conventional QD device without molecular layer. Furthermore, the self-assembled molecular nanolayer of 3-mercaptopropionic acid exhibited a higher luminescent efficiency than 1-propanethiol-based nanolayer owing to the increased hole mobility of thiol-based molecular layer with strong dipole moments.