Perovskite Composite Films Research Articles

Precise Laser-Modulated Anion Exchange on Ultraflexible Perovskite Films for Multicolor Patterns.

Lead halide perovskite anion exchange reactions tend to be spontaneous and rapid. To achieve precise control of anion exchange and modulate the bandgaps of perovskites to meet the demands in full-color displays, a laser-induced liquid-phase anion exchange method is developed in this paper. CsPbBr3 perovskites embedded in a polymer matrix are converted to CsPb(BrxCl1-x)3 and CsPb(BrxI1-x)3 perovskites, realizing the shift from green fluorescence to blue and red fluorescence. By changing the laser parameters, the anion exchange extent and luminescence wavelength are precisely tuned, with the maximum tuning wavelength range of 431-696 nm. Due to the focusing properties of the laser, the spatial position of anion exchange can be precisely controlled, which is significant for realizing fast and accurate patterning without masks. Based on this method, blue patterns with different light-emitting wavelengths are fabricated. RGB three-color patterns on a single perovskite composite film are successfully prepared by further replacement of halogen ions. More importantly, the polymer matrix provides ultraflexibility and good stability for the films; even if the composite films are arbitrarily folded or repeatedly bent, they can still maintain good luminous intensity. This method will show great potential in the field of flexible, full-color displays.

Dielectric, thermal and optical properties of PVDF-based (LaFeO3)0.5 (BaTiO3)0.5 perovskite composite films for advanced technological applications

(1-x)PVDF/(x)LFO-BTO composite films with weight percentages (x = 0, 0.05, 0.1 and 0.15) were prepared by solution casting method. Phase identification was carried out using the X-ray diffraction (XRD) technique revealing different phases (α, β & γ) of PVDF. FTIR results confirmed the presence of different vibrational modes and phases including PVDF phases. AFM and SEM were used to investigate the surface & morphological analysis, the results showed that the surface roughness increased with the concentration of LFO-BTO into PVDF films. From optical absorption spectra, the direct band gap and indirect band gap energies of the PVDF/LFO-BTO were evaluated by incorporating Tauc's relation. The composites experienced a reduction in band gap upon the addition of 0 - 15 wt% of LFO-BTO with an increasing trend in Urbach's energy. The dielectric investigations revealed elevated dielectric constant values across all composites at lower frequency ranges, attributed to interfacial polarization. Specifically, the dielectric constant of 15 % wt of LFO-BTO was found to be much higher (6 times more than the pristine PVDF). Additionally, the dielectric loss was suppressed with increasing filler concentration within the frequency range of 1 KHz to 1 MHz. Impedance spectroscopy analysis depicted a distinctive semi-circular pattern that was linked to the underlying conduction mechanism. The behaviour of ac-conductivity revealed the conduction process following the Nyquist plot. DTA-TGA analysis showed a notable improvement in thermal stability with increasing concentration in the PVDF matrix.

Interactive Deformable Colored Sound Display Achieved with Electrostrictive Fluoropolymer and Halide Perovskite.

The association of color and sound helps human cognition through a synergetic effect like intersensory facilitation. Although soft human-machine interfaces (HMIs) providing unisensory expression have been widely developed, achieving synchronized optic and acoustic expression in one device system has been relatively less explored. It is because their operating principles are different in terms of materials, and implementation has mainly been attempted through structural approaches. Here, a deformable sound display is developed that generates multiple colored lights with large sound at low input voltage. The device is based on alternating-current electroluminescence (ACEL) covered with perovskite composite films. A sound wave is created by a polymer matrix of the ACEL, while simultaneously, various colors are produced by the perovskite films and the blue electroluminescence (EL) emitted from the phosphors in the ACEL. By patterning different colored perovskite films onto the ACELs, associating the color and the sound is successfully demonstrated by a piano keyboard and a wearable interactive device.

Controlling and optimizing amplified spontaneous emission based on CsPbBr3@MCM-41 molecular sieve composite

CsPbX3 (X = Cl, Br, I) perovskites have emerged as promising candidate lasing materials due to their high optical gain, low defect state density, and high absorption coefficient. Unfortunately, they suffer from poor stability, particularly with respect to temperature, moisture, and light exposure, preventing their use in practical optoelectronic applications, such as for amplified spontaneous emission (ASE) with an ultralow laser threshold. Herein, CsPbBr3@MCM-41 molecular sieve (CMM) composites are controllably prepared by different ultrasonication and stirring treatments. In addition, different perovskite concentrations and heat-treatment conditions are also considered to demonstrate the ASE behaviors. In addition, CMM@PS (CMMP) and CMM@AB (CMMA) composites were fabricated successfully by further optimizing the mixing ratio of CMM and the polymer. More excitingly, the stability of the CMM@polymer films with respect to the external environment is greatly improved after the polymer coating. To our surprise, the CMM@ploymer thin films demonstrated ASE at room-temperature, with an ASE threshold as low as 0.136 mJ/cm2 and 0.049 mJ/cm2 for CMMA and CMMP, respectively. These results clearly shed light upon the control and optimization of CsPbBr3 perovskite composite films, paving the way for their widespread use in optoelectronic applications.

Vacuum-Vapor-Deposited 0D/3D All-Inorganic Perovskite Composite Films toward Low-Threshold Amplified Spontaneous Emission and Lasing.

Vacuum vapor deposition (VVD) is a promising way to advancing the commercialization of perovskite light sources owing to its convenience for wafer-scale mass production and compatibility with silicon photonics manufacturing infrastructure. However, the light emission performance of VVD-grown perovskites still lags far behind that of the conventional solution-processed counterparts due to their inferior luminescence properties. Here, a 0D/3D cesium-lead-bromide perovskite composite film is prepared on Si/SiO2 substrates through composition modulation with the VVD method, which exhibits an ultralow amplified spontaneous emission (ASE) threshold down to 14.3 µJ cm-2 in the optimal films, which is on par with that of the solution-processed counterparts. Meanwhile, they also display intriguing operational stability with negligible emission intensity decay under continuous excitation above ASE threshold for 4h in the air. The outstanding ASE performance mainly originates from the reduced trap density and weakened electron-phonon coupling in the 3D CsPbBr3 phase enabled by the incorporation of the 0D Cs4 PbBr6 phase. Finally, by integrating the composite film with the distributed feedback (DFB) cavity, DFB lasing is achieved with a low threshold of 18.2 µJ cm-2 under nanosecond-pulsed laser pumping, which highlights the potential of VVD-processed perovskites for developing high-performance lasers.

Disordered metasurface-enhanced perovskite composite films with ultra-stable and wide color gamut used for backlit displays

Perovskite nanocrystals (PNCs) are promising to replace the traditional phosphor color conversion layers in backlit displays due to their excellent optical properties, which can enhance the color gamut and saturation of displays. However, poor stability and low luminescence efficiency hinder the development of perovskite-based devices. Here, inspired by the Yunnan cicada wing, a low-cost, easy-to-fabricate, and large-area (> 78 cm2) all-dielectric metasurface based on the Purcell effect is developed to tune and improve the light extraction efficiency of PNCs. All-dielectric metasurfaces composed of weakly disordered TiO2/PS spheres are embedded in the PNCs/PVDF (Poly (vinylidene fluoride)) films prepared by in-situ fabrication strategy, resulting in 3.19-fold photoluminescence (PL) maximum enhancement of these composite films. The stability of PNCs is also markedly improved after PVDF encapsulation. As an application demo, these all-dielectric metasurface-modulated perovskite composite films are applied in LCD backlit, with the color gamut of 157% of commercial LCD and 107% of NTSC, showing tremendous potential in high-end lighting and display. Furthermore, combined with the scalability of large-area fabrication, cost-effective weakly disordered metasurfaces are a potential method to bridge the gap between high-efficient laboratory demonstrations and commercialization in the field of display.

Poly(vinylidene fluoride)-Stabilized Black γ-Phase CsPbI3 Perovskite for High-Performance Piezoelectric Nanogenerators.

Halide perovskite materials have been recently recognized as promising materials for piezoelectric nanogenerators (PENGs) due to their potentially strong ferroelectricity and piezoelectricity. Here, we report a new method using a poly(vinylidene fluoride) (PVDF) polymer to achieve excellent long-term stable black γ-phase CsPbI3 and explore the piezoelectric performance on a CsPbI3@PVDF composite film. The PVDF-stabilized black-phase CsPbI3 perovskite composite film can be stable under ambient conditions for more than 60 days and over 24 h while heated at 80 °C. Piezoresponse force spectroscopy measurements revealed that the black CsPbI3/PVDF composite contains well-developed ferroelectric properties with a high piezoelectric charge coefficient (d33) of 28.4 pm/V. The black phase of the CsPbI3-based PVDF composite exhibited 2 times higher performance than the yellow phase of the CsPbI3-based composite. A layer-by-layer stacking method was adopted to tune the thickness of the composite film. A five-layer black-phase CsPbI3@PVDF composite PENG exhibited a voltage output of 26 V and a current density of 1.1 μA/cm2. The output power can reach a peak value of 25 μW. Moreover, the PENG can be utilized to charge capacitors through a bridge rectifier and display good durability without degradation for over 14 000 cyclic tests. These results reveal the feasibility of the all-inorganic perovskite for the design and development of high-performance piezoelectric nanogenerators.

Sulfonic Zwitterion for Passivating Deep and Shallow Level Defects in Perovskite Light‐Emitting Diodes

AbstractChemical passivation via functional additives plays a critical role in achieving high performance perovskite light‐emitting diodes (PeLEDs). Here, perovskite composite films for high performance PeLEDs by using zwitterion 3‐aminopropanesulfonic acid (APS) as the additive are developed. The sulfonic group of APS can simultaneously passivate deep and shallow level defects in perovskites via coordinate and hydrogen bonding, which leads to suppressed non‐radiative recombination and ion migration in the perovskite composite films. Based on this, PeLEDs with a peak external quantum efficiency of 19.2% and a half‐lifetime of 43 h at a constant current density of 100 mA cm−2 are obtained, representing one of the most stable and efficient PeLEDs under high current densities.

Piezophototronic Effect Enhanced Perovskite Solar Cell Based on P(VDF‐TrFE)

As a candidate for next‐generation solar devices, perovskite solar cells are increasingly being studied for their rapid increased power conversion efficiency (PCE). One of the possible routes to further increase PCE is the introduction of polarization in the absorption layer which functions as a method for increasing the built‐in potential and reducing the interface barrier, leading to much improved carrier separation and extraction. This technique uses the principle of the piezophototronic effect utilized for obtaining enhanced optoelectronic performances. Herein, to introduce internal polarization while maintaining optical absorption performance of the perovskite, organic–inorganic hybrid perovskite composite film solar cells are fabricated by doping polarized polyvinylidenefluoride‐co‐trifluoroethylene (P(VDF‐TrFE)) into the perovskite. The composite film is polarized with an external potential, subsequently inducing the piezophototronic effect to enhance the performances of perovskite solar cells. Experimental results show that this simple polarization method has effectively improved several key characteristics of the solar cell. The PCE has reached up to 22.1%, the short‐circuit current (Jsc) increases to 24.2 mA cm−2, and the open‐circuit voltage (Voc) increases to 1.18 V.

Solution-Processed Quasi-Two-Dimensional/Nanoscrystals Perovskite Composite Film Enhances the Efficiency and Stability of Perovskite Light-Emitting Diodes.

Solution-processed quasi-two-dimensional (Q-2D)/colloidal perovskite nanocrystals (PNCs) perovskite composite films are first prepared as the emitting layers of perovskite light-emitting diodes (PeLEDs). The subsequent multi-spin-coating of PNCs not only fills the gully-like fluctuations of the nanocrystal pinning-prepared Q-2D perovskite films and decreases their surface roughness but also transforms the bilayer perovskite nanosheets into multilayer ones, thus improving the charge transport and reducing the hole-injection barrier in the composite films. More importantly, the bromide vacancies and Pb defects in the Q-2D perovskites are removed via Br- supply and Pb-OOC-R interaction, in which the Br ions and COO- groups (from oleic acid) come from the PNC solution, and the radiation recombination is significantly enhanced. Based on the Q-2D/PNCs perovskite composite emitter, the PeLEDs achieve a maximum luminescence of ∼2.0 × 104 cd/m2 and a peak current efficiency of 27.5 cd/A, showing 175 and 337% enhancements compared to the control device with the pristine Q-2D perovskite emitter. The lifetime for the luminance decaying to 50% of the initial intensity increases by a factor of 13.8, demonstrating that the device stability is also improved by the Q-2D/PNCs perovskite composite film.

X-ray detection based on crushed perovskite crystal/polymer composites

Organic-inorganic hybrid perovskite materials have attracted increasing attention in recent years for ionizing radiation detection due to their large cross-section for high energy X-ray or gamma ray, defect-tolerance, large mobility lifetime product, tunable bandgap and facile preparation of single crystals. However, the thickness of solution processed perovskite polycrystalline films are normally limited, and single crystals are fragile and hard to be utilized as a device. In this article, we successfully realized the preparation of the perovskite crystal/polymer composites, through a novel process involving mechanically grinding and sieving. X-ray detectors were fabricated based on the relatively thick composite films via solution process. The device performance under the irradiation of X-rays were also investigated, in terms of stability, dark current, noise and temporal response. Our devices exhibited remarkable performance metrics, which proved that the perovskite composite films can be used to fabricate highly efficient and low-cost X-ray detectors.

Terahertz Absorption in Composite Films Based on Organometallic Perovskite and Mixed Cellulose Ester

Composite films based on CH3NH3PbI3 organometallic perovskite and mixed cellulose ester (CE) were studied using terahertz (THz) spectroscopy in the time domain. It is established that the introduction of CE into CH3NH3PbI3 precursor significantly modifies the parameters of perovskite in the THz range and improves stability of the composite films. In particular, CE addition to the perovskite composite film leads to significant weakening of absorption bands in the region of 1–2 THz related to the excitation of low-frequency oscillatory modes in CH3NH3PbI3 molecules. This can be explained by damping of these modes on CE molecules enveloping the perovskite molecules.

Ultrafast Responsive Non‐Volatile Flash Photomemory via Spatially Addressable Perovskite/Block Copolymer Composite Film

AbstractThe exotic photophysical properties of organic–inorganic hybrid perovskite with long exciton lifetimes and small binding energy have appeared as promising front‐runners for next‐generation non‐volatile flash photomemory. However, the long photo‐programming time of photomemory limits its application on light‐fidelity (Li‐Fi), which requires high storage capacity and short programming times. Herein, the spatially addressable perovskite in polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO)/perovskite composite film as an photoactive floating gate is demonstrated to elucidate the effect of morphology on the photo‐responsive characteristics of photomemory. The chelation between lead ion and PEO segment promotes the anti‐solvent functionalities of the perovskite/PS‐b‐PEO composite film, thus allowing the solution‐processable poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) to act as the active channel. Through manipulating the interfacial area between perovskite and P3HT, fast photo‐induced charge transfer rate of 0.056 ns−1, high charge transfer efficiency of 89%, ON/OFF current ratio of 104, and extremely low programming time of 5 ms can be achieved. This solution‐processable and fast photo‐programmable non‐volatile flash photomemory can trigger the practical application on Li‐Fi.

Modification of Solar Energy Harvesting in Photovoltaic Materials by Plasmonic Nanospheres: New Absorption Bands in Perovskite Composite Film

Thin-film perovskite-based photovoltaics has great potential to make an important contribution to the ongoing search for new sources of clean renewable energy. Excitation of localized surface plasmons in metal nanoparticles could establish a new route for an improvement of the performance of such devices. Using the tools of electrodynamics (Lorenz–Mie theory adopted for absorbing host media), we predict a strong red shift in the spectral activity of gold and silver nanospheres and modification (negative or positive) of white and solar light harvesting in the film of perovskite host caused by centrally distributed plasmonic nanospheres. The enhancement of absorption in perovskite host is proven to be possible for photons with energies close to or smaller than the energy band gap in perovskite, with the final effect depending on the diameter of nanospheres, their concentration, and kind of metal. From the electronic band structure point of view, the predicted strengthening of absorption can be interpreted a...