Organic-inorganic Hybrid Metal Halide Perovskites Research Articles

Unveiling heavy heterovalent doping-modulated microstructure and thermoelectric performance in bulk hybrid perovskite single crystals

Organic-inorganic hybrid metal halide perovskites have emerged as a promising candidate for low-temperature thermoelectric conversion. However, challenges remain in heavily doping bulk perovskite single crystals without phase segregation or self-doping compensation issues to increase the carrier concentration. Previous efforts to enhance their thermoelectric performance rely on photoexcitation or surface/interface doping, which is not suitable for bulk devices to work in dark. This study achieves high monovalent and trivalent doping concentrations of up to 5 % in bulk single crystals of MAPbI3 and MAPbBr3 without phase segregation or defect formation. For monovalent doping, K+ and Li+ are incorporated into the perovskite lattice as interstitials. The resulting lattice distortion/microstrain enhances the electrical conductivity by 10 ∼ 100 times of undoped samples at 420 K. Trivalent doping using SbCl3, BiBr3, and BiI3 significantly enhances the carrier concentration and electrical conductivity, up to 1012 cm−3 and 0.038 S m−1 for MAPbBr3 with 10 % BiI3 at 465 K, respectively, which is 105 times of the undoped samples and 10 times of the best reports on doped MAPbBr3. Interestingly, the Bi3+ dopant oxidizes the deep defect state Pb0, resulting in Bi+ and Pb2+ formation and contributing to the enhanced electrical conductivity. Enhanced thermoelectric figure of merit (ZT) is achieved in MAPbBr3 with 5 % BiI3 at 315 K, almost 100 times of the best reports on doped MAPbBr3. This study provides fundamental understanding of doping-modulated microstructural, charge carrier, and thermoelectric properties of hybrid halide perovskites, offering potential doping strategies to realize the theoretically predicted promising thermoelectric properties in their bulk single crystals for practical thermoelectric devices. The doping-modulated carrier transport will also guide the optimization of optoelectronic applications of halide perovskites for solar cells, light emitters, and photodetectors.

White light emission in 0D halide perovskite [(CH3)3S]2SnCl6·H2O crystals through variation of doping ns2 ions

With the rapid development of white LEDs, the research of new and efficient white light emitting materials has attracted increasing attention. Zero dimensional (0D) organic–inorganic hybrid metal halide perovskites with superior luminescent property are promising candidates for LED application, due to their abundant and tailorable structure. Herein, [(CH3)3S]2SnCl6·H2O is synthesized as a host for dopant ions Bi3+ and Sb3+. The Sb3+ doped, or Bi3+/Sb3+ co-doped, [(CH3)3S]2SnCl6·H2O has a tunable optical emission spectrum by means of varying dopant ratio and excitation wavelength. As a result, we can achieve single-phase materials suitable for emission ranging from cold white light to warm white light. The intrinsic mechanism is examined in this work, to clarify the dopant effect on the optical properties. The high stability of title crystalline material, against water, oxygen and heat, makes it promising for further application.Graphical

Efficient Deep‐Blue Light‐Emitting 2D (100)‐Oriented Perovskites and Spectral Broadening by Exciton Self‐Trapping for White‐light Emissions

AbstractEfficient narrow deep‐blue and broadband emissions in layered 2D organic–inorganic hybrid metal halide perovskites (MHPs) are attracting more attention and need further study. In this work, two (100)‐oriented 2D organic‐inorganic hybrid MHPs of (TFI)2PbBr4 and (TFI)2PbCl4·H2O (TFI = 4‐(trifluoromethyl)‐1H‐imidazole) with efficient deep‐blue and bluish‐white emissions are synthesized and the photoluminescence quantum yields (PLQYs) reached up to 81.21% and 20.23%, respectively. As both intrinsic lattice distortions of two crystals with similar crystal structure are almost negligible, they have theoretical deep‐blue emissions empirically. However, the halogen substitution of chlorine (Cl) by bromine (Br) broadened the deep‐blue photoluminescence to a bluish‐white area. Here, the spectral broadening phenomenon is discussed in detail. The (TFI)2PbBr4 film shows a narrow emission with a 16 nm full width at half maximum (FWHM) peaking at 435 nm upon excitation, and an ultraviolet‐pumped light‐emitting diode (LED) prepared by bluish‐white (TFI)2PbCl4·H2O phosphor shows a color rendering index (CRI) of ≈93 and a related color temperature (CCT) of 4162K, indicating their potential applications in deep‐blue and white LEDs, respectively.

Recent developments in perovskite materials, fabrication techniques, band gap engineering, and the stability of perovskite solar cells

Organic-inorganic hybrid metal halide perovskite solar cells (PSC) represent a novel class of optoelectronic semiconductors that have garnered significant attention from photovoltaic researchers globally. This is due to their continually improving efficiency, straightforward solution processing methods, use of lightweight and cost-effective materials, and other notable features. The advantageous properties of perovskite materials, such as superior charge transport, tunable band gap, and distinctive electronic structure, contribute to their appeal. Over the past 6 to 7 years, diverse device architectures and fabrication techniques for PSC have emerged, achieving an impressive power conversion efficiency (PCE) of 25.7%. This review article primarily focuses on recent advancements in PSC fabrication techniques, synthesis, device architecture, charge transport mechanisms, band gap engineering, and stability. Additionally, it provides a summary of recently reported materials used in various layers of PSC, including the perovskite layer, as well as electron and hole transport layers. Lastly, the article outlines the challenges faced in the development of PSC, offers recommendations, and suggests potential directions for future research to guide the field forward.

Preliminary exploration of the influence of N+/NHx+ ions/groups bombardment at TiO2 ETLs on performance of MAPbI3 perovskite solar cells

The service stability of organic–inorganic hybrid metal halide perovskite solar cells (PSCs) is one of most important factors, which is seriously influenced by the decomposition of perovskite layer. Especially, the decomposition of perovskite layer could deteriorate the interface between perovskite layer and TiO2 electron transport layer (ETL). In this work, TiO2 ETLs are prepared by the sputtering technique and traditional spin-coating technique. Then, TiO2 ETLs are bombarded by N+/NHx+ ions/groups. PSCs with all TiO2 ETLs are prepared and measured. The results show that after bombardment, N+/NHx+ ions/groups could chemically react with Ti/O ions at surface of TiO2 ETLs. As a result, the conduction band minimum and transfer resistance of TiO2 ETLs both deteriorate, which decrease the power conversion efficiency of PSCs seriously. While, because anatase TiO2 (001) crystal face consists of saturated O/Ti ions and displays the highest surface free energy, TiO2 ETLs with anatase (001) preferred orientation displays the optimal restraint on deterioration of power conversion efficiency caused by N+/NHx+ ions/groups bombardment. Based on above results, TiO2 ETLs with anatase (001) preferred orientation should be the optimal one for PSCs, which could improve the service stability obviously.

Regulation strategy of white emission from organic–inorganic hybrid metal halide perovskites

In this review, the structure, photophysical properties, and white-light mechanism of organic–inorganic hybrid metal halide perovskites with white emission are summarized, with an emphasis on the adjustment strategy for white-light performance.

Stabilized Preparation of Fiber-Shaped Perovskite Solar Cells with Ti and Graphene Substrates

Organic–inorganic hybrid metal halide perovskite solar cells (PSCs) have made dramatic progress over the past few years. Fiber-shaped PSCs (FPSCs) extend the application of PSCs to wearable and portable electronics. The one-dimensional flexible structure of the fiber substrate and the high efficiency photoelectric conversion ability of the perovskite materials make FPSCs promising for energy applications. However, FPSCs have limited preparation methods and show poorer optoelectronic performance compared to conventional PSCs. In our work, we present a multiple quantitative coating preparation method, which was optimized by controlling the PbI2 concentration and the cycle number of coating process. We demonstrated the effectiveness of the methods in improving the film performance, with a photoelectric conversion efficiency (PCE) of 5.2% under air. The applicability of the multiple quantitative coating methods was studied by the FPSCs fabricated on reduced graphene fibers (rGFs), which present PCEs of about 1.5%. In addition, by extending the length of rGFs, the device performance was further improved. Thus, we demonstrated a stable fabrication method of FPSCs based on rGFs, which exhibited significant potential for using PSCs as a power source in wearable devices.

Amorphous TiO2 film with fiber like structure: An ideal candidate for ETL of perovskite solar cells

• E T L A m o r p h o u s T i O 2 was prepared by DCP-MS at room temperature. • Lots fiber like structures run through the E T L A m o r p h o u s T i O 2 directly. • Fiber like structures in E T L A m o r p h o u s T i O 2 improves electron transfer efficiency. • PCE of PSCs improves from 4.7% of E T L A n a t a s e T i O 2 to 11.5% of E T L A m o r p h o u s T i O 2 . Organic-inorganic hybrid metal halide perovskite solar cells (PSCs) with planar heterojunction structures were fabricated. The amorphous and anatase TiO 2 electron transfer layer (ETL) was deposited by the direct current pulsed magnetron sputtering technology. With the ordinary CH 3 NH 3 PbI 3 , PSCs with amorphous and anatase TiO 2 ETL showed the average power conversion efficiency in (11.5 ± 0.7)% and (4.7 ± 1.5)%, respectively. Combining with XRD and TEM results, the fiber like structure in amorphous TiO 2 ETL resulted in the increase of average power conversion efficiency of PSCs. Finally, amorphous TiO 2 with fiber like structure is an ideal ETL for PSCs, which is prepared by sputtering.

Improving the performance of perovskite solar cells via TiO2 electron transport layer prepared by direct current pulsed magnetron sputtering

Organic-inorganic hybrid metal halide perovskite solar cells (PSCs) with planar heterojunction structures were fabricated. The traditional methylammonium lead iodide (CH3NH3PbI3, MAPbI3) was selected as the photovoltaic convert layer. The TiO2 electron transport layer (ETL) was prepared by the sol-gel and direct current pulsed magnetron sputtering (DC-PMS) technologies. PSCs with Sol-gel and DC-PMS TiO2 ETLs showed power conversion efficiencies of 13.4% and 16.1%, respectively. The detailed measurement results showed that the DC-PMS TiO2 ETL contained high-density chain-like structures, which consisted of nanosized anatase TiO2 nuclei. Compared with the short-circuit current of 20.08 mA/cm2 for PSCs with Sol-gel TiO2 ETL, the chain-like structure in the DC-PMS TiO2 ETL could effectively improve the short-circuit current to 22.11 mA/cm2. In addition, compared with the hysteresis index of 38.5% for PSCs with Sol-gel TiO2 ETL, the chain-like structure and higher surface potential of the DC-PMS TiO2 ETL could effectively reduce the hysteresis index to 14.9%. Finally, because of the whole room temperature preparation process, DC-PMS technology is an ideal candidate for flexible application of PSCs, which could be applied to the organic substrate without resistance to high temperature.

The Pnictogen Bond, Together with Other Non-Covalent Interactions, in the Rational Design of One-, Two- and Three-Dimensional Organic-Inorganic Hybrid Metal Halide Perovskite Semiconducting Materials, and Beyond.

The pnictogen bond, a somewhat overlooked supramolecular chemical synthon known since the middle of the last century, is one of the promising types of non-covalent interactions yet to be fully understood by recognizing and exploiting its properties for the rational design of novel functional materials. Its bonding modes, energy profiles, vibrational structures and charge density topologies, among others, have yet to be comprehensively delineated, both theoretically and experimentally. In this overview, attention is largely centered on the nature of nitrogen-centered pnictogen bonds found in organic-inorganic hybrid metal halide perovskites and closely related structures deposited in the Cambridge Structural Database (CSD) and the Inorganic Chemistry Structural Database (ICSD). Focusing on well-characterized structures, it is shown that it is not merely charge-assisted hydrogen bonds that stabilize the inorganic frameworks, as widely assumed and well-documented, but simultaneously nitrogen-centered pnictogen bonding, and, depending on the atomic constituents of the organic cation, other non-covalent interactions such as halogen bonding and/or tetrel bonding, are also contributors to the stabilizing of a variety of materials in the solid state. We have shown that competition between pnictogen bonding and other interactions plays an important role in determining the tilting of the MX6 (X = a halogen) octahedra of metal halide perovskites in one, two and three-dimensions. The pnictogen interactions are identified to be directional even in zero-dimensional crystals, a structural feature in many engineered ordered materials; hence an interplay between them and other non-covalent interactions drives the structure and the functional properties of perovskite materials and enabling their application in, for example, photovoltaics and optoelectronics. We have demonstrated that nitrogen in ammonium and its derivatives in many chemical systems acts as a pnictogen bond donor and contributes to conferring stability, and hence functionality, to crystalline perovskite systems. The significance of these non-covalent interactions should not be overlooked, especially when the focus is centered on the rationale design and discovery of such highly-valued materials.

Photoinduced large polaron transport and dynamics in organic–inorganic hybrid lead halide perovskite with terahertz probes

Organic-inorganic hybrid metal halide perovskites (MHPs) have attracted tremendous attention for optoelectronic applications. The long photocarrier lifetime and moderate carrier mobility have been proposed as results of the large polaron formation in MHPs. However, it is challenging to measure the effective mass and carrier scattering parameters of the photogenerated large polarons in the ultrafast carrier recombination dynamics. Here, we show, in a one-step spectroscopic method, that the optical-pump and terahertz-electromagnetic probe (OPTP) technique allows us to access the nature of interplay of photoexcited unbound charge carriers and optical phonons in polycrystalline CH3NH3PbI3 (MAPbI3) of about 10 μm grain size. Firstly, we demonstrate a direct spectral evidence of the large polarons in polycrystalline MAPbI3. Using the Drude–Smith–Lorentz model along with the Frӧhlich-type electron-phonon (e-ph) coupling, we determine the effective mass and scattering parameters of photogenerated polaronic carriers. We discover that the resulting moderate polaronic carrier mobility is mainly influenced by the enhanced carrier scattering, rather than the polaron mass enhancement. While, the formation of large polarons in MAPbI3 polycrystalline grains results in a long charge carrier lifetime at room temperature. Our results provide crucial information about the photo-physics of MAPbI3 and are indispensable for optoelectronic device development with better performance.

A Comparison of Charge Carrier Dynamics in Organic and Perovskite Solar Cells.

The charge carrier dynamics in organic solar cells and organic-inorganic hybrid metal halide perovskite solar cells, two leading technologies in thin-film photovoltaics, are compared. The similarities and differences in charge generation, charge separation, charge transport, charge collection, and charge recombination in these two technologies are discussed, linking these back to the intrinsic material properties of organic and perovskite semiconductors, and how these factors impact on photovoltaic device performance is elucidated. In particular, the impact of exciton binding energy, charge transfer states, bimolecular recombination, charge carrier transport, sub-bandgap tail states, and surface recombination is evaluated, and the lessons learned from transient optical and optoelectronic measurements are discussed. This perspective thus highlights the key factors limiting device performance and rationalizes similarities and differences in design requirements between organic and perovskite solar cells.

Tuning Dielectric Transitions in Two-Dimensional Organic-Inorganic Hybrid Lead Halide Perovskites.

Organic-inorganic hybrid metal halide perovskites possessing unique two-dimensional (2D)-layered structures have been demonstrated with excellent molecular tunability and stability, especially the promising semiconductor properties for solar cell applications. In this work, three 2D lead halide organic-inorganic hybrid perovskites (IAA)2PbX4 (IAA = isoamylammonium cation and X = Cl, Br, and I) were synthesized by employing a solution processing method and demonstrate distinct tuning solid-state phase transitions coupled with dielectric responses, as well as light absorption properties. Among the title perovskites, the phase transition temperature decreases gradually, and their band gap also indicates a narrowing trend. The results are mainly derived from slight changes in the crystal structure by halogen regulation. These findings might provide an effective crystal engineering strategy for exploring high-performance functional perovskite materials.

Coupling of organic cation and inorganic lattice in methylammonium lead halide perovskites: Insights into a pressure-induced isostructural phase transition

Organic-inorganic hybrid metal-halide perovskite (OIHP) materials provide a tunable platform for engineering their optoelectronic properties. Although several high-pressure studies have been conducted from the OIHP family of single crystals and films, the exact nature of the dynamic coupling of the $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}$ (MA) cation with the octahedral lattice framework and the mechanisms responsible for the structural phase transformation under pressure are not well captured. By combined photoluminescence (PL), synchrotron-based x-ray diffraction, and Raman-scattering studies as a function of pressure from methylammonium lead bromide ($\mathrm{M}\mathrm{A}\mathrm{Pb}{\mathrm{Br}}_{3}$), we shed light on an isostructural phase transition due to the coupling of the MA cation and the $\mathrm{Pb}{\mathrm{Br}}_{6}$ lattice through hydrogen bonding. The sharp discontinuities at $\ensuremath{\sim}$ 1 GPa and $\ensuremath{\sim}$ 3 GPa in the PL peak positions correlate with the structural changes observed in high-pressure XRD and Raman-scattering studies. The electronic band edge as a function of pressure is calculated within density-functional theory. The PL peak position, intensity and width of the excitonic peak show significant changes at 2 GPa, which corroborate the changes observed in high-pressure Raman-scattering studies. The frequencies of the lattice modes and the C--H/N--H bending and stretching modes of the MA cation show anomalous changes and other nuances at 2 GPa. The suppression of rotational and orientational disorder of the organic moiety is initiated at 2 GPa and the ordering is completed by 3.0 GPa, leading to an order-disorder type cubic II ($Im\overline{3}$) to orthorhombic ($Pnma$) phase transition. Along with the revelation of an isostructural transformation at 2 GPa, this paper highlights the impact of molecular vibrations on the electronic properties of $\mathrm{M}\mathrm{A}\mathrm{Pb}{\mathrm{Br}}_{3}$ under pressure.

Zero-Dimensional Hybrid Cd-Based Perovskites with Broadband Bluish White-Light Emissions.

Recently, low-dimensional organic-inorganic hybrid metal halide perovskites acting as single-component white-light emitting materials have attracted extensive attention, but most studies concentrate on hybrid lead perovskites. Herein, we present two isomorphic zero-dimensional (0D) hybrid cadmium perovskites, (HMEDA)CdX4 (HMEDA=hexamethylenediamine, X=Cl (1), Br (2)), which contain isolated [CdX4 ]2- anions separated by [HMEDA]2+ cations. Under UV light excitation, both compounds display broadband bluish white-light emission (515 nm for 1 and 445 nm for 2) covering the entire visible light spectrum with sufficient photophysical stabilities. Remarkably, compound 2 shows a high color rendering index (CRI) of 83 enabling it as a promising candidate for single-component WLED applications. Based on the temperature-dependent, powder-dependent and time-resolved PL measurements as well as other detailed studies, the broadband light emissions are attributed to self-trapped excitons stemming from the strong electron-phonon coupling.

Interface passivation strategy improves the efficiency and stability of organic–inorganic hybrid metal halide perovskite solar cells

Abstract

Quantitative Modeling of Self-Assembly Growth of Luminescent Colloidal CH3NH3PbBr3 Nanocrystals

The organic–inorganic hybrid metal halide perovskites with different dimensions and diverse architectures are highly attractive materials for optoelectronic applications. However, people know little about the dynamics of their formation processes. Here, we study both experimentally and theoretically the self-assembly formation dynamics of the luminescent colloidal CH3NH3PbBr3 nanocrystals. We have observed their successive transformations from original spherical quantum dots to periodically stacked nanoplatelets when the primitive colloidal nanocrystals with a high concentration were maintained in liquid for a prolonged period of time. A theoretical dynamic collision model by taking into account the popular van der Waals force, the polarization force that is unique for the perovskites, and the electrostatic forces between particle surfaces in the presence of the surface ligands is proposed to explain the self-assembly process of the colloidal CH3NH3PbBr3 nanocrystals. The result reveals that the rather ea...

Simultaneously boost diffusion length and stability of perovskite for high performance solar cells

Organic-inorganic hybrid metal-halide perovskites, such as methylammonium lead iodide, have emerged as amazing semiconductors with immense potential in thin film photovoltaic owing to their impressive diffusion lengths. However, the instability of these perovskites in ambient air, due to the presence of hydrophilic and volatile organic cation, hinders their further commercialization. Although low-dimensional perovskite solar cells (PSCs) show better stability than conventional three-dimensional (3D) devices, the low power conversion efficiency (PCE) is delivered, due to the decline of carrier mobility and diffusion length. Here, a large organic cation, tert-butylammonium (t-BA), is incorporated into the 3D perovskite, which not only enhances the crystal stability, but also greatly reduces the trap density and improves the mobility of the perovskite film, leading to ∼1.8 μm electron and hole diffusion lengths. High-performance PSCs based on t-BA0.1[Cs0.05(FA0.83MA0.17)0.95]0.9Pb(I0.83Br0.17)3 with champion PCEs of 20.62% (19.8% ± 0.4%) for 0.04 cm2 and 14.54% for 20.8 cm2 are demonstrated. More importantly, with humidity of 45–55%, the solar cells could sustain 80% of their “post burn-in” PCE after continuous working under light (AM1.5G, 100 mW cm−2) in air for 1174 h. This lifetime is 63% longer than that (718 h) of the control Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3 PSCs.

Growth of Metal Halide Perovskite, from Nanocrystal to Micron-Scale Crystal: A Review

Metal halide perovskite both in the form of nanocrystal and thin films recently emerged as the most promising semiconductor material covering a huge range of potential applications from display technologies to photovoltaics. Colloidal inorganic and organic–inorganic hybrid metal halide perovskite nanocrystals (NCs) have received tremendous attention due to their high photoluminescence quantum yields, while large grain perovskite films possess fewer defects, and a long diffusion length providing high-power conversion efficiency in planar devices. In this review, we summarize the different synthesis routes of metal halide perovskite nanocrystals and the recent methodologies to fabricate high-quality micron scale crystals in the form of films for planar photovoltaics. For the colloidal synthesis of halide perovskite NCs, two methods including ligand-assisted reprecipitation and hot injection are mainly applied, and the doping of metal ions in NCs as well as anion exchange reactions are widely used to tune their optical properties. In addition, recent growth methods and underlying mechanism for high-quality micron size crystals are also investigated, which are summarized as solution-process methods (including the anti-solvent method, solvent vapor annealing technology, Ostwald ripening, additive engineering and geometrically-confined lateral crystal growth) and the physical method (vapor-assisted crystal growth).

Electrode quenching control for highly efficient CsPbBr3 perovskite light-emitting diodes via surface plasmon resonance and enhanced hole injection by Au nanoparticles

Compared to organic–inorganic hybrid metal halide perovskites, all-inorganic cesium lead halides (e.g, CsPbBr3) hold greater promise in being emissive materials for light-emitting diodes owing to their superior optoelectronic properties as well as their higher stabilities. However, there is still considerable potential for breakthroughs in the current efficiency of CsPbBr3 perovskite light-emitting diodes (PeLEDs). Electrode quenching is one of the main problems limiting the current efficiency of PeLEDs when poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is used as the hole injection layer. In this work, electrode quenching control was realized via incorporating Au NPs into PEDOT:PSS. As a result, the CsPbBr3 PeLEDs realized an improvement in maximum luminescence ranging from ∼2348 to ∼7660 cd m−2 (∼226% enhancement) and current efficiency from 1.65 to 3.08 cd A−1 (∼86% enhancement). Such substantial enhancement of the electroluminescent performance can be attributed to effective electrode quenching control at the PEDOT:PSS/CsPbBr3 perovskite interface via the combined effects of local surface plasma resonance coupling and enhanced hole transportation in the PEDOT:PSS layer by Au nanoparticles.