Planar-integrated single-crystalline perovskite photodetectors

By: Osman M. Bakr

Here we produce large-area planar-integrated films made up of large perovskite single crystals. These crystalline films exhibit mobility and diffusion length comparable with those of single crystals. Using this technique, we produced a high-performance light detector showing high gain (above 104 electrons per photon) and high gain-bandwidth product (above 108Hz) relative to other perovskite-based optical sensors.

CH3NH3PbCI3 Single Crystals: Inverse Temperature Crystallization and Visible-Blind UV-Photodetector

By: Osman M. Bakr

Here we present a new method of growing sizable CH3NH3PbCI3 single crystals based on the retrograde solubility behavior of hybrid perovskites. We show, for the first time, the energy band structure, charge recombination, and transport properties of CH3NH3PbCI3 single crystals. These crystals exhibit trap-state density, charge carrier concentration, mobility, and diffusion length comparable with the best quality crystals of methylammonium lead iodide or bromide perovskites reported so far. The high quality of the crcystal along with its suitable optical band gap enabled us to build an efficient visible-blind UV-photodetector, demonstrating its potential in optoelectric applications.

Solution-Processed Visible-Blind Ultraviolet Photodetectors with Nanosecond Response Time and High Detectivity

By: Zhaolai Chen, Osman M. Bakr

We propose high-performance solution-processed visible-blind UV photodetectors by growing a few micrometer-thick MAPbCI3 thin single crystals with smooth surfaces, as well as free of the pinholes and grain boundaries that are highly detrimental to the charge carrier lifetime and mobility apparent in polycrystalline perovskite films. The small thickness of the MAPbCI3 single crystal ensures effective carrier collection and altrafast response speen. Moreover, the smooth surface without pinholes and grain boundaries suppresses the leakage current. These essential characteristics for the MAPbCI3 thin single crystals could not have been achieved without a strategy to judiciously designing the subtrates'

All-inorganic perovskite nanocrystal scintillators

By: Qiushui Chen, Osman M. Bakr, Xiaogang Liu

We demonstrated inorganic perovskite nanocrystals as a new class of scintillators that are capable of converting small doses of X-ray photons into multicolour visible light. When considering the material’s solution-processability and practical scalability, it is envisioned that these scintillators are suitable for the mass production of ultrasensitive X-ray detectors and large-area, flexible X-ray imagers. Compared to conventional CsI:Tl scintillators—whose use is constrained by the risk of thallium poisoning, the presence of afterglow and high-temperature synthesis—perovskite nanocrystals offer several outstanding attributes, including relatively low toxicity, low-temperature solution synthesis, fast scintillation response and high emission quantum yield.

Metal Halide Perovskite Nanosheet for X-ray High-Resolution Scintillation Imaging

By: Yuhai Zhang, Osman M. Bakr, Omar F. Mohammed

We report the room-temperature synthesis of a colloidal scintillator comprising CsPbBr3 nanosheets of large concentration (up to 150 mg/mL). The CsPbBr3 colloid exhibits a light yield (∼21000 photons/MeV) higher than that of the commercially available Ce:LuAG single-crystal scintillator (∼18000 photons/MeV). Scintillators based on these nanosheets display both strong radioluminescence (RL) and long-term stability under X-ray illumination. Importantly, the colloidal scintillator can be readily cast into a uniform crack-free large-area film (8.5 × 8.5 cm2 in area) with the requisite thickness for high-resolution X-ray imaging applications.

High-speed colour-converting photodetector with all-inorganic CsPbBr3 perovskite...

By: Chun Hong Kang, Ibrahim Dursun, Guangyu Liu,Lutfan Sinatra, Osman M. Bakr, Boon S. Ooi

We report a hybrid Si-based photodetection scheme by incorporating CsPbBr3 perovskite nanocrystals (NCs) as a UV-to-visible colour-converting layer for high-speed solar-blind UV communication. With the addition of the NC layer, a nearly threefold improvement in the responsivity and an increase of ~25% in the external quantum efficiency (EQE) of the solar-blind region compared to a commercial silicon-based photodetector were observed. A high data rate of up to 34 Mbps in solar-blind communication was achieved using the hybrid CsPbBr3–silicon photodetection scheme in conjunction with a 278-nm UVC light-emitting diode (LED). These findings demonstrate the feasibility of an integrated high-speed photoreceiver design of a composition-tuneable perovskite-based phosphor and a low-cost silicon-based photodetector for UV communication.

Perovskite Nanocrystals as a Color Converter for Visible Light Communication

By: Ibrahim Dursun, Jun Pan, Osman M. Bakr

We present a promising light converter for VLC by designing solution-processed CsPbBr3 perovskite nanocrystals (NCs) with a conventional red phosphor. The fabricated CsPbBr3 NC phosphor-based white light converter exhibits an unprecedented modulation bandwidth of 491 MHz, which is ∼40 times greater than that of conventional phosphors, and the capability to transmit a high data rate of up to 2 Gbit/s. Moreover, this perovskite-enhanced white light source combines ultrafast response characteristics with a high color rendering index of 89 and a correlated color temperature of 3236 K, thereby enabling dual VLC and solid-state lighting functionalities.

A New Generation of Luminescent Materials Based on Low‐Dimensional Perovskites

By: Jun Pan, Lutfan Sinatra, Marat Lutfullin, Ibrahim Dursun, Osman M. Bakr

In this article, properties of two emerging types of low‐dimensional perovskites are discussed, including perovskite quantum dots CsPbX3 (X = Cl, Br or I) and zero‐dimensional perovskite Cs4PbBr6. Moreover, their application for light down conversion in LCD backlighting systems and in visible light communication are also presented.

Novel Techniques for Highly Stable Luminescent Perovskite Halide Quantum Dots

By: Lutfan Sinatra, Marat Lutfullin Abdullah Saud Abbas, Jun Pan, Osman M. Bakr

The present work shows the further progress in enhancement of perovskite QDs stability, resistance to photodegradation and PL quenching at high temperatures.

Bidentate Ligand-Passivated CsPbI3 Perovskite Nanocrystals for Stable Near...

By: Jun Pan, Lutfan Sinatra, Osman M. bakr

We develop a postsynthesis passivation process for CsPbI3 NCs by using a bidentate ligand, namely 2,2′-iminodibenzoic acid. Our passivated NCs exhibit narrow red photoluminescence with exceptional quantum yield (close to unity) and substantially improved stability. The passivated NCs enabled us to realize red light-emitting diodes (LEDs) with 5.02% external quantum efficiency and 748 cd/m2 luminance, surpassing by far LEDs made from the nonpassivated NCs.

Solution‐Grown Monocrystalline Hybrid Perovskite Films for Hole‐Transporter‐Free...

By: Wei Peng, Lingfei Wan, Banavoth Murali, Kang‐Ting Ho, Ashok Bera, Namchul Cho...

High‐quality perovskite monocrystalline films are successfully grown through cavitation‐triggered asymmetric crystallization. These films enable a simple cell structure, ITO/CH3NH3PbBr3/Au, with near 100% internal quantum efficiency, promising power conversion efficiencies (PCEs) >5%, and superior stability for prototype cells. Furthermore, the monocrystalline devices using a hole‐transporter‐free structure yield PCEs ≈6.5%, the highest among other similar‐structured CH3NH3PbBr3 solar cells to date.

Single-Crystal MAPbI3 Perovskite Solar Cells Exceeding 21% Power Conversion Efficiency

By: Zhaolai Chen, Osman M. Bakr.

Twenty-micrometer-thick single-crystal methylammonium lead triiodide (MAPbI3) perovskite (as an absorber layer) grown on a charge-selective contact using a solution space-limited inverse-temperature crystal growth method yields solar cells with power conversion efficiencies reaching 21.09% and fill factors of up to 84.3%. These devices set a new record for perovskite single-crystal solar cells and open an avenue for achieving high fill factors in perovskite solar cells.

Low-Temperature Crystallization Enables 21.9% Efficient Single-Crystal MAPbI3...

By: Abdullah Y. Alsalloum, Osman M. Bakr

We devise a solvent-engineering approach to reduce the crystallization temperature of MAPbI3 single-crystal films (<90 °C), yielding better quality films with longer carrier lifetimes. Single-crystal MAPbI3 inverted PSCs fabricated with this strategy show markedly enhanced open-circuit voltages (1.15 V vs 1.08 V for controls), leading to power conversion efficiencies of up to 21.9%, which are among the highest reported for MAPbI3-based devices.

Managing grains and interfaces via ligand anchoring enables 22.3%-efficiency...

By: Xiaopeng Zheng, Osman M. Bakr

We demonstrate the use of long AALs with an optimized alkyl-chain length as grain and interface modifiers to improve optoelectronic properties by promoting favourable grain orientation and suppressing trap-state density. These augmented film properties enable the demonstration of a record certified PCE of >22.3% (23.0% PCE for lab-measured champion devices) for inverted-structured devices. The devices show no PCE loss after 1,000 h of operation at the MPP under simulated AM1.5 illumination.

Highly Efficient Perovskite‐Quantum‐Dot Light‐Emitting Diodes by Surface...

By: Jun Pan, Lutfan Sinatra, Osman M. Bakr

A two‐step ligand‐exchange strategy is developed, in which the long‐carbon‐ chain ligands on all‐inorganic perovskite (CsPbX3, X = Br, Cl) quantum dots (QDs) are replaced with halide‐ion‐pair ligands. Green and blue light‐emitting diodes made from the halide‐ion‐pair‐capped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.

Chlorine Vacancy Passivation in Mixed Halide Perovskite Quantum Dots by Organic...

By: Xiaopeng Zheng, Osman M. Bakr

We report a strategy for passivating Cl vacancies in MHP quantum dots (QDs) using nonpolar solvent-soluble organic pseudohalide [n-dodecylammonium thiocyanate (DAT)], enabling blue MHP LEDs with greatly enhanced efficiency. DAT-treated CsPb(BrxCl1–x)3 QDs exhibit near unity (∼100%) photoluminescence quantum yields, and their blue (∼470 nm) LEDs are spectrally stable with an external quantum efficiency of 6.3%, a record for perovskite LEDs emitting in the range of 460–480 nm relevant to Rec. 2020 display standards, and a half-lifetime of ∼99 s.

Thermochromic Perovskite Inks for Reversible Smart Window Applications

By: Michele De Bastiani, Lutfan Sinatra, Osman M. Bakr

We utilized the unusual crystallization process of perovskites along with their tunable optical properties to design a simple synthesis of inks for TC applications. These inks exhibit a completely reversible chromatic variation ranging from yellow to black as the temperature increases from 25 to 120 °C. These properties pave the way for a new class of smart windows and camouflage coatings with an unprecedented range of color based on hybrid metal halide perovskites.

Pure Cs4PbBr6: Highly Luminescent Zero-Dimensional Perovskite Solids

By: Makhsud I. Saidaminov, Jun Pan, Osman M. Bakr

We introduced a simple method for the separation of the monophasic Cs4PbBr6 solid and studied its emission properties. Cs4PbBr6 showed outstandingly high PLQY compared to its 3D perovskite counterpart and other perovskite derivatives reported in the literature. The coexistence of both 0D and 3D phases in previous reports on Cs4PbBr6 solids, as we showed here, has a severe detrimental effect on the emissive properties of 0D perovskites.

Ligand-Free Nanocrystals of Highly Emissive Cs4PbBr6 Perovskite

By: Yuhai Zhang, Lutfan Sinatra, Osman M. Bakr, Omar F. Mohammed

We report a new approach to preparing ligand-free perovskite NCs of Cs4PbBr6, which retained high photoluminescence quantum yield (44%). Such an approach involves a polar solvent (acetonitrile) and two small molecules (ammonium acetate and cesium chloride), which replace the organic ligand and still protect the nanocrystals from dissolution. The successful removal of hydrophobic long ligands was evidenced by Fourier transform infrared spectroscopy, ζ potential analysis, and thermogravimetric analysis. Unlike conventional perovskite NCs that are extremely susceptible to polar solvents, the ligand-free Cs4PbBr6 NCs show robust resistance to polar solvents.

Automated Synthesis of Photovoltaic-Quality Colloidal Quantum Dots Using...

By: Jun Pan, Osman M. Bakr

We report a strategy for flow reactor synthesis of PbS CQDs and prove that it leads to solar cells having performance similar to that of comparable batch-synthesized nanoparticles. Specifically, we find that, only when using a dual-temperature-stage flow reactor synthesis reported herein, are the CQDs of sufficient quality to achieve high performance. We use a kinetic model to explain and optimize the nucleation and growth processes in the reactor. Compared to conventional single-stage flow-synthesized CQDs, we achieve superior quality nanocrystals via the optimized dual-stage reactor, with high photoluminescence quantum yield (50%) and narrow full width-half-maximum.

High-quality bulk hybrid perovskite single crystals within minutes by inverse...

By: Makhsud I. Saidaminov, Osman M. Bakr

MAPbX3 perovskites exhibit inverse temperature solubility behaviour in certain solvents. This novel phenomenon in hybrid perovskites enabled us to design an innovative crystallization method for these materials, referred to here as inverse temperature crystallization (ITC), to rapidly grow high-quality size- and shape-controlled single crystals of both MAPbBr3 and MAPbI3, at a rate that is an order of magnitude faster than the previously reported growth methods. The versatility of our approach provides the continuous enlargement of crystals, through replacement of the depleted growth solution, and the use of templates for controlling their shapes.

Perovskite-Based Artificial Multiple Quantum Wells

By: Kwang Jae Lee, Lutfan Sinatra, Osman M. Bakr

We demonstrate a facile approach for fabricating perovskite-based artificial MQWs using commonly available thermal evaporator systems. These MQWs are directly built from CsPbBr3 perovskite layers and 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBi) barriers. These CsPbBr3/TPBi artificial MQWs, of type-I band alignment, enable precise and arbitrary control over quantum wells/barriers and their spatially aligned multiple-stacking configuration, without requiring specific substrates as epitaxial growth normally entails.(37,38) The CsPbBr3/TPBi artificial MQWs, which are polycrystalline in nature, exhibited tunable optical characteristics related to the well/barrier thicknesses and stacking configurations, including thickness-dependent carrier transitions and confinement, multiwavelength emissions, the quantum tunneling effect (in temperature-dependent photoluminescence, TDPL), and long-lived hot carriers.