Halide Perovskite Nanocrystals Research Articles

Imbedded Perovskite Nanocrystals in Metal Halide Microcrystal: Synthesis and Heterostructure

AbstractLead halide perovskite nanocrystals and other metal halides have received considerable attention due to their unique optoelectronic properties. A combined perovskite nanocrystal‐metal halide heterostructure can achieve desirable properties for enriched applications. However, the construction of such a heterostructure is challenging. In this study, a CsPbBr3/Cs2ZnBr4 heterostructured microcrystal with perovskite nanocrystals embedded in a metal halide matrix is successfully synthesized using a facile ultrasound‐assisted post‐processing method. The heterostructure of the perovskite‐metal halide composite materials is fully deciphered through ab initio calculations and multiscale characterizations. The heterostructure‐induced variation in optical properties is elucidated based on micro‐nano spectral and luminescence kinetic behaviors. This study provides new insights into the design of perovskite nanocrystal‐based heterostructured materials, improving the understanding of metal halides and extending their applications.

Lead‐Free Halide Perovskite Materials and Optoelectronic Devices: Progress and Prospective

AbstractHalide perovskites, in the form of thin films and colloidal nanocrystals, have recently taken semiconductor optoelectronics research by storm, and have emerged as promising candidates for high‐performance solar cells, light‐emitting diodes (LEDs), lasers, photodetectors, and radiation detectors. The impressive optical and optoelectronic properties, along with the rapid increase in efficiencies of solar cells and LEDs, have greatly attracted researchers across many disciplines. However, most advances made so far in terms of preparation (colloidal nanocrystals and thin films), and the devices with highest efficiencies are based on Pb‐based halide perovskites, which have raised concerns over their commercialization due to the toxicity of Pb. This has triggered the search for lower‐toxicity Pb‐free halide perovskites and has led to significant progress in the last few years. In this roadmap review, researchers of different expertise have joined together to summarize the latest progress, outstanding challenges, and future directions of Pb‐free halide perovskite thin films and nanocrystals, regarding their synthesis, optical spectroscopy, and optoelectronic devices, to guide the researchers currently working in this area as well as those that will join the field in the future.

Cesium lead bromide perovskite nanocrystals for the visual detection of chloride ions: A review

Lead halide perovskite nanocrystals (NCs) have been extensively studied due to their high quantum yield, high color purity, tunable band gap, and simple preparation methods. Among them, cesium lead bromide perovskite NCs (CsPbBr3 NCs) have the characteristics of good stability performance, better luminous performance, and good halide exchange properties, etc., and a visual sensing system for fluorescence wavelength shift can be constructed by using their spectral tunability. Accordingly, CsPbBr3 has become a potential candidate material for on-site detection of chloride ions, providing possibility for tunable visual analysis, which not only expands the application potential of CsPbBr3 NCs in the detection field, but also greatly improves the visual fluorescence sensing method. On a basis of the halide exchange property of CsPbBr3 NCs, this review introduces the development strategy of perovskites as the probes to detect chloride ions in the environments of liquids, solids, and gases, and summarizes and prospects the new methods of chloride detection over CsPbBr3 NCs. In addition, this review provides an overview of existing challenges, providing reference for the development of highly sensitive and long-term stable chloride probes based on lead halide perovskites.

Enhanced luminescence stability of high-entropy dual-phase Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)Br3/Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)2Br5 perovskite nanocrystals coated with SiO2 and EVA

All-inorganic halide perovskite nanocrystals (NCs) have attracted much attention in many fields. However, the poor stability of NCs and the toxicity of Pb have greatly hindered their practical applications. Reducing the proportion of Pb with the concept of high-entropy and coating NCs with an outer layer have been regarded as effective strategies to solve the problems. Herein, We have successfully synthesized the all-inorganic high-entropy dual-phase Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)Br3/Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)2Br5(Cs‘B’Br3/Cs‘B’2Br5) perovskite NCs with good luminescence properties by a high-energy ball milling method; On the basis of which, Cs‘B’Br3/Cs‘B2’Br5 NCs are coated with SiO2 and EVA resin. Due to the amorphous SiO2 protection, the Cs‘B’Br3/Cs‘B2’Br5@SiO2 NCs maintained 93% of their emission intensity after 90 days compared to their uncoated counterparts. The PL intensity of Cs‘B’Br3/Cs‘B2’Br5 NCs /EVA was significantly enhanced by a factor of 4.7 for compared to the uncoated NCs. In addition, the PL emission intensity of the Cs‘B’Br3/Cs‘B2’Br5 NCs /EVA remained 93.7% after 90 days, and the emission peak intensity remained approximately 63% after 8 h of placement in an enclosed environment at 80% humidity through the dense polymer chains and the hydrophobic nature of the film. Finally, the film could expand its application prospects in the field of flexible device.

Fabrication of CH3NH3SnCl3 perovskite nanocrystal-based electrode for supercapacitor devices application

Lead-free halide perovskites nanocrystals (NCs) have been widely used not only in the field of optoelectronics but also in energy storage applications like electrochemical supercapacitors, which could replace electrochemical batteries due to their high power density and long cycle life. The low energy density of supercapacitors is one of the main reasons why they have limited commercial applications. Herein, we have reported synthesis of 3D methylammonium tin chloride perovskite (MASnCl3) nanocrystals (NCs) via a ligand-assisted re-precipitation process (LARP) and determined its performance as an electrochemical supercapacitor. The formation of MASnCl3 NCs is confirmed by different characterization tools. The supercapacitor performances of the synthesized NCs are studied by using three-electrode electrochemical measurements. The maximum specific capacitance, energy density, and power density are found to be 2050 Fg−1, 12 kWKg−1, and 102 WhKg−1, respectively. The charge storage mechanism is estimated from the power law equation by studying the diffusion-limited and capacitive processes and it has been found that the capacitance is 94.16 % capacitive to 5.84 % diffusive in nature. The supercapacitor performance of the synthesized MASnCl3 NCs are studied by fabricating a metal coin-based two-electrode system in which PVA-H2SO4 as solid state electrolyte and NCs act as an active material. The device has retained 80.7 % of its initial specific capacitance value even after 1000 GCD cycles. Interestingly, the developed device showed almost similar gravimetric capacitance value and is enabled to glow a light emitting diode (LED) smoothly.

Accelerated room temperature synthesis of desired cesium lead halide perovskite nanocrystals via automated microfluidic meta learner

Cesium lead halide perovskite nanocrystals (CLHP NCs) have demonstrated their unique optical properties in next-generation lighting and display devices through controlling the size, shape, and composition. However, achieving their target-specific synthesis with numerous reaction parameters via traditional methods requires long and tedious optimization. Herein, a fully automated microfluidic meta learner (AMML) coupled with coiled flow inverter reactors (CFIR) is developed for facilely synthesizing desired CLHP NCs. CFIR offers a strong support in reagent mixing for AMML, producing high-quality NCs with negligible by-products. By concatenating the model-agnostic meta-learning and feedback control, AMML provides quick and accurate locating of target emission CsPb(BrxI1-x)3 NCs in the wide range from 519 nm to 636 nm based on 3 data points, even in the no-prior-knowledge part. AMML exhibits excellent screening ability (25 experiments in 110 min) of reaction parameters for controllable synthesis of CsPbBr3 NCs. Based on the optimal results, a white light-emitting diode is fabricated with excellent stability and a wide color gamut of 121 % NTSC. AMML offers a novel paradigm for the large-scale synthesis of desired NCs and can be applied to other NCs for intelligent and sustainable discovery.

Chiral Lead Halide Perovskite Nanocrystals: Construction Strategies and Photophysical Properties

AbstractLead halide perovskite nanocrystals (PeNCs) have attracted intense interest by virtue of their numerous remarkable optoelectronic properties, which render them promising for various optoelectronic applications. Over the past few years, substantial progress has been made in the study of chiral PeNCs, from the sample preparation, spectroscopic characterization to practical applications. In this review, the state‐of‐the‐art progress of the construction strategies and photophysical properties of chiral PeNCs has been summarized. The focus is placed on emerging developments in terms of synthetic methods, chiroptical properties, nonlinear optics, and chiral spintronics in chiral PeNCs. In the end, there is a discussion on the current challenges and future prospects in this versatile, rapidly evolving field.

Lead-Free Halide Perovskite Nanocrystals for Light-Emitting Diodes.

Lead-based halide perovskite nanocrystals (PeNCs) have demonstrated remarkable potential for use in light-emitting diodes (LEDs). This is because of their high photoluminescence quantum yield, defect tolerance, tunable emission wavelength, color purity, and high device efficiency. However, the environmental toxicity of Pb has impeded their commercial viability owing to the restriction of hazardous substances directive. Therefore, Pb-free PeNCs have emerged as a promising solution for the development of eco-friendly LEDs. This review article presents a detailed analysis of the various compositions of Pb-free PeNCs, including tin-, bismuth-, antimony-, and copper-based perovskites and double perovskites, focusing on their stability, optoelectronic properties, and device performance in LEDs. Furthermore, we address the challenges encountered in using Pb-free PeNC-LEDs and discuss the prospects and potential of these Pb-free PeNCs as sustainable alternatives to lead-based PeLEDs. In this review, we aim to shed light on the current state of Pb-free PeNC LEDs and highlight their significance in driving the development of eco-friendly LED technologies.

Dynamic Observations on Formation of Coffee-Ring Structures from the Degradation of Cesium Lead Halide Perovskite Nanocrystals.

Nanomaterials of halide perovskites have attracted increasing attention for their remarkable potential in optoelectronic devices, but their instability to environmental factors is the core issue impeding their applications. In this context, the microscopic understanding of their structural degradation mechanisms upon external stimuli remains incomplete. Herein, we took an emerging member of this material family, Cs4PbBr6 nanocrystals (NCs), as an example and investigated the degradation pathways as well as underlying mechanisms under an electron beam by using in situ transmission electron microscopy. Our atomic-scale study identified the distinct degradation stages for the NCs toward interesting coffee-ring PbBr2 structures, which are caused by the organic surface capping agents as well as surface energy of NCs. Our findings present a fundamental insight for the degradation of halide perovskite NCs and may provide indispensable guidance for their structural design and stability improvement.

Toward the Controlled Synthesis of Lead Halide Perovskite Nanocrystals.

Lead halide perovskite nanocrystals (LHP NCs) have rapidly emerged as one of the most promising materials for optical sources, photovoltaics, and sensor fields. The controlled synthesis of LHP NCs with high monodispersity and precise size tunability has been a subject of intensive research in recent years. However, due to their ionic nature, LHP NCs are usually formed instantaneously, and the corresponding nucleation and growth are difficult to monitor and regulated. In this Perspective, we summarize the representative attempts to achieve controlled synthesis of LHP NCs. We first highlight the burst nucleation and rapid growth characteristics of conventional synthesis methods. Afterward, we introduce the scheme of changing the LHP NCs into kinetically dominant, continuously size-tunable synthesis via nucleation-growth decoupling. We also summarize methods to eliminate undesired ripening effects and achieve homogeneous size distribution through rational ligand selection and solvent engineering. We hope this Perspective will facilitate the development of controlled LHP NCs synthesis protocols and advance the understanding of crystal growth fundamentals of perovskite materials.

Layer‐By‐Layer Printed Metal Hybrid (Cs:FA)PbI3 Perovskite Nanocrystal Solar Cells

AbstractMixed halide perovskite nanocrystals in the form of cesium/formamidinium lead triiodide ((Cs:FA)PbI3) offer great potential for efficient and stable solar cells. To date, large‐scale production with roll‐to‐roll compatible deposition methods remains difficult and requires detailed research on each involved processing step. Here, a proof‐of‐concept study about slot‐die coating (printing) the active layer of (Cs:FA)PbI3‐based nanocrystal solar cells is presented. Structural and morphological changes during ligand exchange of long‐chain oleic acid and oleylamine by Pb(NO3)2, and top‐layer FAI passivation are investigated. Ligand exchange improves the processability of the nanocrystal layer and enhances charge transport. It also changes texture from face‐on toward edge‐on orientation as grazing‐incidence X‐ray scattering studies indicate. Ligand exchange and FAI passivation redshift photoluminescence and prolong charge carrier lifetime in the printed nanocrystal films. The proof‐of‐concept feasibility of printing metal halide perovskite nanocrystal films for solar cells is shown by building 20 devices with a median power conversion efficiency of 6.39%.

Tailoring the Electron and Hole Landé Factors in Lead Halide Perovskite Nanocrystals by Quantum Confinement and Halide Exchange.

The tunability of the optical properties of lead halide perovskite nanocrystals makes them highly appealing for applications. Halide anion exchange and quantum confinement enable tailoring of the band gap. For spintronics, the Landé g-factors of electrons and holes are essential. Using empirical tight-binding and k·p methods, we calculate them for nanocrystals of all-inorganic lead halide perovskites CsPbX3 (X = I, Br, Cl). The hole g-factor band gap dependence follows the universal law found for bulk perovskites, while for electrons, a considerable modification is predicted. Based on the k·p analysis, we conclude that this difference arises from the interaction of the bottom conduction band with the spin-orbit split electron states. These predictions are confirmed experimentally for electron and hole g-factors in CsPbI3 nanocrystals in a glass matrix, measured by time-resolved Faraday ellipticity in a magnetic field at cryogenic temperatures.

Pt-CsPbBr3 Perovskite Nanocrystal Heterostructures: All Epitaxial.

Designing heterostructures of soft ionic nanocrystals with metallic or covalent nanostructures having epitaxial junctions in solution poses several fundamental challenges. Hence, in spite of large successes in developing lead halide perovskite nanocrystals, the chemistry of formation of their facet-directive epitaxial growth of noble metals cannot be explored yet. To address this, herein, epitaxial heterostructures of orthorhombic CsPbBr3 and cubic Pt in multiple directional approaches are reported. Appropriate facets of perovskite nanocrystals and high-temperature reaction are the key parameters for obtaining such nanocrystal heterostructures. Interfacial planes at the junctions having ideal lattice matching helped in establishing the epitaxial relations of (110) of orthorhombic (space group Pbnm) CsPbBr3 with {020} of cubic Pt and again (011) of CsPbBr3 with {111} of Pt. These results provided strong fundamental insights that ionic halide perovskite nanostructures and materials having different crystal phases can be placed in a single building block with continuous sublattice structures.

(Invited) Charge Carrier Relaxation, Recombination and Extraction Dynamics in Metal Halide Perovskite Nanocrystals

Charge Carrier Relaxation, Recombination and Extraction Dynamics in Metal Halide Perovskite Nanocrystals Anunay Samanta School of Chemistry, University of Hyderabad, Hyderabad 500046 (anunay@uohyd.ac.in)The lead halide-based all-inorganic and hybrid perovskites are under intense investigation due to their immense potential in solar photovoltaic and light emitting applications.1,2 As realization of the full potential of these materials in various applications requires a clear understanding of the relaxation pathways and dynamics of the photo-generated charge carriers, we have been studying these key photo-processes in a wide range of perovskite nanocrystals.3-10 In this talk, we would like to present some of our recent results highlighting how a combination of femtosecond pump-probe and single-particle fluorescence techniques can be used to obtain valuable information on the nature and energy states of the photogenerated species, pathways and dynamics of relaxation of the charge carriers, location and nature of the trap states and their role in fluctuation of the photoluminescence of different caesium lead halide (CsPbX3) perovskite nanocrystals. References Dey, A. et. al. ACS Nano 2021, 15, 10775.Green, M.A.; Ho-Baillie, A.; Snaith, H.J. Nature Photonics 2014, 8, 506.Mondal, N; De, A.; Das, S.; Paul, S.; Samanta, A. Nanoscale 2019, 4, 9796.Mondal, N; De, A.; Samanta, A. ACS Energy Letts. 2019, 4, 32.Seth, S.; Ahmed, T.; Samanta, A. J. Phys. Chem. Lett. 2018, 9, 7007.Mondal, N; De, A.; Samanta, A. J. Phys. Chem. Lett. 2018, 9, 3673.Ahmed, T; Seth. S.; Samanta, A. ACS Nano 2019, 13, 13537.De, A.; Das, A.; Samanta, A. ACS Energy Letts. 2020, 5, 2246.Ahmed, T.; Paul, S.; Samanta, A. J. Phys. Chem. C 2022, 126, 9109.Paul, S.; Samanta, A. J. Phys. Chem. Lett. 2022, 13, 5742.

Ultrafast and Radiation-Hard Lead Halide Perovskite Nanocomposite Scintillators.

The use of scintillators for the detection of ionizing radiation is a critical aspect in many fields, including medicine, nuclear monitoring, and homeland security. Recently, lead halide perovskite nanocrystals (LHP-NCs) have emerged as promising scintillator materials. However, the difficulty of affordably upscaling synthesis to the multigram level and embedding NCs in optical-grade nanocomposites without compromising their optical properties still limits their widespread use. In addition, fundamental aspects of the scintillation mechanisms are not fully understood, leaving the scientific community without suitable fabrication protocols and rational guidelines for the full exploitation of their potential. In this work, we realize large polyacrylate nanocomposite scintillators based on CsPbBr3 NCs, which are synthesized via a novel room temperature, low waste turbo-emulsification approach, followed by their in situ transformation during the mass polymerization process. The interaction between NCs and polymer chains strengthens the scintillator structure, homogenizes the particle size distribution and passivates NC defects, resulting in nanocomposite prototypes with luminescence efficiency >90%, exceptional radiation hardness, 4800 ph/MeV scintillation yield even at low NC loading, and ultrafast response time, with over 30% of scintillation occurring in the first 80 ps, promising for fast-time applications in precision medicine and high-energy physics. Ultrafast radioluminescence and optical spectroscopy experiments using pulsed synchrotron light further disambiguate the origin of the scintillation kinetics as the result of charged-exciton and multiexciton recombination formed under ionizing excitation. This highlights the role of nonradiative Auger decay, whose potential impact on fast timing applications we anticipate via a kinetic model.

Chiral Ligand‐Induced Inversion and Tuning of Excitonic Optical Activity in Intrinsically Chiral CsPbBr3 Perovskite Nanoplatelets

AbstractOwing to their attractive optical and chiroptical properties, chiral metal halide perovskites have received increasing attention, with potential applications ranging from photonics and optoelectronics to spintronics. Metal halide perovskite nanocrystals with either intrinsic or extrinsic (e.g., chiral ligand‐induced) chirality have been reported recently, and the interplay between these two types of chirality has yet to be addressed. Herein, the inversion and tuning of excitonic optical activity is reported in intrinsically chiral perovskite nanoplatelets, originating from interactions between their structural chirality (due to the spontaneously formed screw dislocations in the crystalline lattice) and the surface enantiomeric (R/S) chiral ligands R/S‐phenylethylammonium bromide. Through post‐preparative exposure of the perovskite nanoplatelets to these R/S ligands of varied contents, either chiral ligand‐induced intrinsic chirality inversion or negative and positive Cotton effects induced by the ligands via electronic coupling between the ligand and the nanoplatelets are identified. These findings deepen understanding of the modulation of excitonic optical activity in chiral perovskites and can guide the rational design and synthesis of novel chiral materials.

Liquid‐solid‐Interpenetration Surface Reconstruction of Monodisperse Water Stabilized CsPbBr3/CsPb2Br5 Core/Shell Perovskite Nanocrystals

AbstractAll‐inorganic lead halide perovskite nanocrystals (NCs) have shown great potential in various optoelectronic device applications due to their excellent optoelectronic properties, but their poor stability remains a key obstacle to widespread application. The preparation of core/shell NCs is developed to improve their stability, but most of the coating for single NCs is incomplete, and the crystal orientation and interface binding of core/shell structures are still unclear. Here, a surface reconstruction strategy to synthesize CsPbBr3/CsPb2Br5 core/shell NCs with uniform coating structure is reported. The concentration of [PbBr8]6− monomer in the system is regulated by creating local low H2O concentration conditions to balance the erosion of perovskite by water and the overall heterogeneous nucleation reaction system, resulting in single encapsulated and well‐edged perovskite core/shell NCs. More importantly, advanced characterization tools are used to reveal the core/shell structural features of CsPbBr3/CsPb2Br5 core/shell NCs at the atomic scale, which has not been reported before, and the interface matching of the two‐phase binding is simulated by density functional theory calculations, which confirm that the CsPb2Br5 (116) facet can bind to the CsPbBr3 (100) facet with the lowest binding energy. The prepared core/shell perovskite NCs can still retain photoluminescence emission after >30 days in water.

One-step synthesis of all-inorganic high-entropy dual-phase Cs‘B’Br3/Cs‘B’2Br5 perovskite nanocrystals by high-energy ball milling

All-inorganic lead halide perovskite nanocrystals (NCs) have attracted considerable attention in field of optoelectronics due to their excellent properties such as high PLQY, tunable emission spectra in visible light region, and narrow emission peaks. However, problems existing in the research of all-inorganic lead halide perovskite materials are high lead content, low stability, and complex synthesis processes. Those problems need to be solved urgently. Therefore, dual-phase Cs‘B’Br3/Cs‘B’2Br5 perovskite material (Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)Br3/Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)2Br5) was synthesized by doping the B-site of CsPbBr3 and CsPb2Br5 using high-energy ball milling in this thesis. This dual-phase perovskite material has maximum absorption edge of 540 nm, a band gap width of 2.22 eV, the maximum emission peak at 600 nm with FWHM of 72 nm, PLQY of 24.50%, and an average fluorescence lifetime of 227.87 μs. After 21 days at room temperature, luminescent intensity of NCs increased to 156%, and still retained 109% at 120 days. After treatment at 150 °C, luminescent intensity decreased to 47%. Results show that this high-entropy dual-phase perovskite has great stability in different temperature. This proves that synthesis of high-entropy dual-phase halide perovskite by high-energy ball milling is feasible, and has great significance in solving poor stability and high lead content of all-inorganic lead halide perovskite in the future.

Highly Luminescent and Stable Halide Perovskite Nanocrystals by Interfacial Defect Passivation and Amphiphilic Ligand Capping.

Halide vacancies cause lattice degradation and nonradiative losses in halide perovskites. In this study, we strategically fill bromide vacancies in CsPbBr3 perovskite nanocrystals with NaBr, KBr, or CsBr at the organic-aqueous interface for hydrophobic ligand-capped nanocrystals or in a polar solvent (2-propanol) for amphiphilic ligand-capped nanocrystals. Energy-dispersive X-ray spectra, powder X-ray diffraction data, and scanning transmission electron microscopy images help us confirm vacancy filling and the structures of samples. The bromide salts increase the photoluminescence quantum yield (98 ± 2%) of CsPbBr3 by decreasing the nonradiative decay rate. Single-particle studies show the quantum yield increase originates from the poorly luminescent nanocrystals becoming highly luminescent after filling vacancies. Furthermore, we tune the optical band gap (ultraviolet-visible-near-infrared) of the hydrophobic ligand-capped nanocrystals by halide exchange at the toluene-water interface using saturated NaCl or NaI solutions, which completes in about 60 min under continuous mixing. In contrast, the amphiphilic ligand accelerates the halide exchange in 2-propanol, suggesting ambipolar functional groups speed up the ion-exchange reaction. The bromide vacancy-filled or halide-exchanged samples in a toluene-water biphasic solvent show higher stability than amphiphilic ligand-capped samples in 2-propanol. This strategy of defect passivation, ion exchange, and ligand chemistry to improve quantum yields and tune band gaps of halide perovskite nanocrystals can be promising for designing stable and water-soluble perovskite samples for solar cells, light-emitting diodes, photodetectors, and photocatalysts.

Unraveling the Relevance of Electron and Hole Transfer in Lead Halide Perovskite Nanocrystals on Current Conduction.

Optimization of perovskite-based optoelectronic performance demands prudent engineering in the device architecture with facile transport of generated charge carriers. Herein, we explore the charge transfer (CT) kinetics in perovskite nanocrystals (PNCs), CsPbBr3, with two redox-active quinones, menadione (MD) and anthraquinone (AQ), and its alteration in halide exchanged CsPbCl3. With a series of spectroscopic and microscopic measurements, we infer that both electron and hole transfer (ET-HT) prevail in CsPbCl3 with quinones, resulting in a faster CT, while ET predominates for CsPbBr3. Furthermore, current-sensing atomic force microscopy measurements demonstrate that the conductance across a metal-PNC-metal nanojunction is improved in the presence of quinones. The contributions of ET and HT to current conduction across PNCs are well supported and validated by theoretical calculations of the density of states. These outcomes convey a new perspective on the relevance of ET and HT in the optimal current conduction and optoelectronic device engineering of perovskites.