Organic-inorganic Metal Halide Perovskites Research Articles

Anisotropic Electron-Phonon Interactions in 2D Lead-Halide Perovskites.

Two-dimensional (2D) hybrid organic-inorganic metal halide perovskites offer enhanced stability for perovskite-based applications. Their crystal structure's soft and ionic nature gives rise to strong interaction between charge carriers and ionic rearrangements. Here, we investigate the interaction of photogenerated electrons and ionic polarizations in single-crystal 2D perovskite butylammonium lead iodide (BAPI), varying the inorganic lamellae thickness in the 2D single crystals. We determine the directionality of the transition dipole moments (TDMs) of the relevant phonon modes (in the 0.3-3 THz range) by the angle- and polarization-dependent THz transmission measurements. We find a clear anisotropy of the in-plane photoconductivity, with a ∼10% reduction along the axis parallel with the transition dipole moment of the most strongly coupled phonon. Detailed calculations, based on Feynman polaron theory, indicate that the anisotropy originates from directional electron-phonon interactions.

Advances in Mixed Tin-Lead Narrow-Bandgap Perovskites for Single-Junction and All-Perovskite Tandem Solar Cells.

Organic-inorganic metal-halide perovskites have received great attention for photovoltaic (PV) applications owing to their superior optoelectronic properties and the unprecedented performance development. For single-junction PV devices, although lead (Pb)-based perovskite solar cells have achieved 26.1% efficiency, the mixed tin-lead (Sn-Pb) perovskites offer more ideal bandgap tuning capability to enable an even higher performance. The Sn-Pb perovskite (with a bandgap tuned to ≈1.2eV) is also attractive as the bottom subcell for a tandem configuration to further surpass the Shockley-Queisser radiative limit for the single-junction devices. The performance of the all-perovskite tandem solar cells has gained rapid development and achieved a certified efficiency up to 29.1%. In this article, the properties and recent development of state-of-the-art mixed Sn-Pb perovskites and their application in single-junction and all-perovskite tandem solar cells are reviewed. Recent advances in various approaches covering additives, solvents, interfaces, and perovskite growth are highlighted. The authors also provide the perspective and outlook on the challenges and strategies for further development of mixed Sn-Pb perovskites in both efficiency and stability for PV applications.

Strain in Hybrid Organic-Inorganic Metal Halide Perovskites Microstructures by Numerical Simulations.

Hybrid organic-inorganic metal halide perovskites (HOIPs) are promising materials for optoelectronics applications. Their optical and electrical properties can be controlled by strain engineering, that results from application of local elastic deformation or deposition on pre-patterned substrates acquiring a conformal 3D shape. Most interesting, their mechanical properties depend on their crystal structure, composition and dimensionality. We explore by numerical simulations the deformation of a selection of HOIPs comprising a broad range of elastic properties. We consider an axial symmetry with the formation of microdomes on flakes. Radial and vertical forces are considered, finding that the radial force is more effective to obtain large deformation. Large vertical displacement and strain is obtained for HOIPs with low stiffness. The layered nature of HOIPs, that are formed by inorganic layers of different thickness and organic spacers, is also investigated, revealing a non-monotonous trend with the proportion of inorganic to organic part.

Piperidine and Pyridine Series Lead-Free Dion-Jacobson Phase Tin Perovskite Single Crystals and Their Applications for Field-Effect Transistors.

Two-dimensional (2D) organic-inorganic metal halide perovskites have gained immense attention as alternatives to three-dimensional (3D) perovskites in recent years. The hydrophobic spacers in the layered structure of 2D perovskites make them more moisture-resistant than 3D perovskites. Moreover, they exhibit unique anisotropic electrical transport properties due to a structural confinement effect. In this study, four lead-free Dion-Jacobson (DJ) Sn-based phase perovskite single crystals, 3AMPSnI4, 4AMPSnI4, 3AMPYSnI4, and 4AMPYSnI4 [AMP = (aminomethyl)-piperidinium, AMPY = (aminomethyl)pyridinium] are reported. Results reveal structural differences between them impacting the resulting optical properties. Namely, higher octahedron distortion results in a higher absorption edge. Density functional theory (DFT) is also performed to determine the trends in energy band diagrams, exciton binding energies, and formation energies due to structural differences among the four single crystals. Finally, a field-effect transistor (FET) based on 4AMPSnI4 is demonstrated with a respectable hole mobility of 0.57 cm2 V-1 s-1 requiring a low threshold voltage of only -2.5 V at a drain voltage of -40 V. To the best of our knowledge, this is the third DJ-phase perovskite FET reported to date.

Revealing the Roles of Guanidine Hydrochloride Ionic Liquid in Ion Inhibition and Defects Passivation for Efficient and Stable P erovskites Solar Cells.

As a result of full-scale ongoing global efforts, the power conversion efficiency (PCE) of the organic-inorganic metal halide perovskite has skyrocketed. Unfortunately, the long-term operational stability for commercialization standards is still lagging owing to intrinsic defects such as ion migration-induced degradation, undercoordinated Pb2+, and shallow defects initiated by disordered crystal growth. Herein, we employed multifunctional, non-volatile tetra-methyl guanidine hydrochloride [TMGHCL] ionic liquid (IL) as an additive to elucidate defects' passivation effects on organic-inorganic metal halide perovskite. More specifically, the formation of hydrogen bonds between H+ in GA+ and I- and coordinate bonding between Cl- and undercoordinated PbI2+could significantly passivate these defects. The hypothesis was confirmed by both experimental and DFT simulations displaying that the optimized ratio of IL integration restrains ion migration, improving grains' size, and significantly elongating the carrier lifetime. Remarkably, the modified cell achieved a peak efficiency of 22.00% with negligible hysteresis, compared to the control device's PCE of 20.12%. In addition, the TMGHCL-based device retains its 93.29% efficiency after 16 days of continuous exposure to air. This efficient approach of adding IL to perovskites absorber can produce high PCE and has strong commercialization potential.

Pyrrolidinium Derivative‐Based Ionic Liquid Achieves Defect Passivation for Efficient Perovskite Solar Cells Exceeding 23%

In the rapidly developing field of photovoltaics, organic–inorganic metal halide perovskites are outstanding for their exceptional power conversion efficiencies (PCE), exceeding 26%. However, the full potential of these materials is often undermined by the prevalence of defects within their structure and at the grain surfaces, leading to significant nonradiative recombination losses. To meet this critical challenge, this study introduces a novel strategy involving a pyrrolidinium derivative and tetrafluoroborate ionic liquid, specifically 2‐pyrrolidin‐1‐ium‐1‐ethylammonium tetrafluoroborate (PyE(BF4)2), as an additive in the perovskite precursor. This approach aims to meticulously control crystallization processes and effectively passivate defects on the surface and grain boundaries of the perovskite. The formation of N─H…I− hydrogen bonds and strong ionic interactions, PyE(BF4)2 not only stabilizes the [PbI6]4− framework but also optimizes the valence band alignment with the hole transport layer. Empirical results demonstrate that perovskite solar cells modified with PyE(BF4)2 have achieved a notable PCE of 23.80% and remarkable stability exceeding 1300 h under standard testing protocols (ISOS‐V‐1). The findings emphasize the transformative potential of multifunctional ionic liquids in enhancing the performance and durability of perovskite‐based photovoltaic devices, marking a significant step forward in pursuing sustainable and efficient solar energy solutions.

Unraveling Interface-Driven and Loss Mechanism-Centric Phenomena in 3D/2D Halide Perovskites: Prospects for Optoelectronic Applications.

In recent years, organic-inorganic metal halide perovskite solar cells (PSCs) have attracted considerable interest due to their remarkable and rapidly advancing efficiencies. Over the past decade, PSC efficiencies have significantly approached those of state-of-the-art silicon-based photovoltaics, making them a promising material. Currently, the scientific community widely recognizes the performance of 3D-PSCs and 2D-PSCs individually. However, when both are combined to form a heterostructure, the lattice and charge dynamics at the interface undergo a multitude of mechanisms that affect their performance. The interface between heterostructures facilitates the degradation of PSCs. The degradation pathways can be attributed to lattice distortions, inhomogeneous energy landscapes, interlayer ion migration, nonradiative recombination, and charge accumulation. This Review is dedicated to examining the phenomena that arise at the interface of 3D/2D halide perovskites and their related photophysical properties and loss mechanism processes. We mainly focus on the impact of lattice mismatch, energy level alignment, anomalous carrier dynamics, and loss mechanisms. We propose a "cause-impact-identify-rectify" approach to gain a comprehensive understanding of the ultrafast processes occurring within the material. Finally, we highlight the importance of advanced spectroscopic and imaging techniques in unraveling these intricate mechanisms. This discussion delves into the future possibilities of fabricating 3D/2D heterostructure-based optoelectronic devices, pushing the boundaries of performance across diverse fields. It envisions the creation of devices with unparalleled capabilities, exceeding the limitations of current technologies.

Preparation of two-dimensional perovskite layer by solution method for improving stability of FAPbI<sub>3</sub> perovskite solar cells

Organic-inorganic metal halide perovskite solar cells (PSCs) have been widely studied due to their excellent photoelectric conversion performance, but the inherent chemical instability of CH(NH<sub>2</sub>)<sub>2</sub>PbI<sub>3</sub> (FAPbI<sub>3</sub>) hinders its sustainable development. In particular, the surface interface of the membrane has prominent humidity sensitivity due to lower activation energy, the defect of the surface interface has a strong correlation with the film stability, and the treatment result of the defect is one of the key factors to improve the long-term stability. The FAPbI<sub>3</sub> suffers phase transition from black perovskite phase to yellow non-perovskite phase at room temperature, and the moisture will accelerate this phase transition. Interface engineering is one of the common methods to improve the stability of perovskite solar cells. In addition to interface engineering, there is a strategy of stacking a two-dimensional (2D) perovskite layer on the surface for interface passivation. However, most of the preparation methods of 2D perovskite layer have limitations. In this work, the full solution method and post-treatment mode of annealing are adopted, the hybrid perovskite solar cells of vitamin perovskite are successfully fabricated. The FAPbI<sub>3</sub> perovskite surface is uniformly spin-coated with butylamine iodide (BAI) solution, and the formation of 2D perovskite is driven on the surface of FAPbI<sub>3</sub> perovskite. Due to the passivation of surface interface defects by the 2D perovskite layer, the non-radiative recombination of charge carriers is reduced, greatly improving the carrier lifetime. Because of the hydrophobicity of long chain molecules in 2D perovskite, the long-term stability of the device is significantly improved. Consequently, the unencapsulated device containing 2D perovskite layer remains above 80% after operating at room temperature in ambient air with a relative humidity (RH) of 60% for nearly 1000 hours. The 2D perovskite layer can significantly improve the long-term stability of the film without affecting the charge carrier transport performance. This method of improving the stability of the device by constructing 2D perovskite layer is in line with the requirements and development trend of high-quality perovskite solar cells, and is a strategy with great development potential.

Revealing Unusual Bandgap Shifts with Temperature and Bandgap Renormalization Effect in Phase‐Stabilized Metal Halide Perovskite Thin Films

AbstractHybrid organic–inorganic metal halide perovskites are emerging materials in photovoltaics, whose bandgap is one of the most crucial parameters governing their light‐harvesting performance. This work presents the temperature and photocarrier density dependence of the bandgap in two phase‐stabilized perovskite thin films (MA0.3FA0.7PbI3 and MA0.3FA0.7Pb0.5Sn0.5I3) using photoluminescence and absorption spectroscopy. Contrasting bandgap shifts with temperature are observed between the two perovskites. Using X‐ray diffraction and in situ high‐pressure photoluminescence spectroscopy, it is shown that thermal expansion plays only a minor role in the large bandgap blueshift, which is attributed to the enhanced structural stability of the samples. The first‐principles calculations further demonstrate the significant impact of thermally induced lattice distortions on the bandgap widening. It is proposed that the anomalous trends are caused by the competition between static and dynamic distortions. Additionally, both the bandgap renormalization and band‐filling effects are directly observed for the first time in fluence‐dependent photoluminescence measurements and are employed to estimate the exciton effective mass. The results provide new insights into the basic understanding of thermal and charge‐accumulation effects on the band structure of hybrid perovskite thin films.

Investigating the Performance of Efficient and Stable Planer Perovskite Solar Cell with an Effective Inorganic Carrier Transport Layer Using SCAPS-1D Simulation

Organic–inorganic metal halide perovskite (OIMHP) has emerged as a promising material for solar cell application due to their outstanding optoelectronics properties. The perovskite-based solar cell (PSC) demonstrates a significant enhancement in efficiency of more than 20%, with a certified efficiency rating of 23.13%. Considering both the Shockley limit and bandgap, there exists a substantial potential for further efficiency improvement. However, stability remains a significant obstacle in the commercialization of these devices. Compared to organic carrier transport layers (CTLs), inorganic material such as ZnO, TiO2, SnO2, and NiOX offer the advantage of being deposited using atomic layer deposition (ALD), which in turn improves the efficiency and stability of the device. In this study, methylammonium lead iodide (MAPbI3)-based cells with inorganic CTL layers of SnO2 and NiOX are simulated using SCAPS-1D software. The cell structure configuration comprises ITO/SnO2/CH3NH3PbI3/NiOX/Back contact where SnO2 and NiOX act as ETL and HTL, respectively, while ITO is a transparent front-end electrode. Detailed investigation is carried out into the influence of various factors, including MAPbI3 layer size, the thickness of CTLs, operating temperature parasitic resistance, light intensity, bulk defects, and interfacial defects on the performance parameters. We found that the defects in layers and interface junctions greatly influence the performance parameter of the cell, which is eliminated through an ALD deposition approach. The optimum size of the MAPbI3 layer and CTL was found to be 400 nm and 50 nm, respectively. At the optimized configuration, the PSC demonstrates an efficiency of 22.13%, short circuit current (JSC) of 20.93 mA/m2, open circuit voltage (VOC) of 1.32 V, and fill factor (FF) of 70.86%.

Dimension-Controlled Synthesis of Hybrid-Mixed Halide Perovskites for Solar Cell Application.

Despite the rapid improvement of photovoltaic (PV) efficiency in hybrid organic-inorganic metal halide perovskites (HOIPs), the fabrication procedure of a compact thin film in a large-area application is still a tedious work. Apart from the quality of the thin film, the stability of the perovskite materials and the expensive organic hole transport layer (HTL) within the HOIP-based PV device are the major issues that need to be addressed prior to their commercialization. Herein, a unique glass rod-based facile fabrication technique for producing a compact and stable thin film utilizing a mixed-halide-based perovskite precursor solution is demonstrated. The fabricated devices deliver high photoconversion efficiency (PCE) without the use of any HTL and show an excellent stability under ambient conditions. By varying the organic CH3NH3I (MAI) and inorganic PbBr2 content, perovskite materials with different dimensions, i.e., 3D, 2D, and 1D, are synthesized to produce an active layer for PV devices. Although a 2D single-halide perovskite is reported earlier, herein two different mixed-halide 2D perovskites, i.e., MA2PbI2Br2 and MAPb2IBr4, are synthesized successfully, and their performance is compared in detail along with that of 1D and 3D mixed-halide perovskites. The facile synthesized mixed-halide 2D-based MA2PbI2Br2 perovskite shows a PCE of 10.14% with a high stability of 92% after 100 days without encapsulation, which is much superior as compared to that of the mixed-halide 3D MAPbIBr2. The semiconducting behavior as well as the nature of the bandgap of the synthesized compounds is examined by pursuing density functional theory calculations. Specifically, the role of iodine doping to modify the electronic band structure is investigated, and introduction of iodine is found to reduce the effective masses of both electrons and holes in the perovskite material.

Lead-free CsCu2Br3 perovskite for multilevel resistive switching memory

Organic–inorganic metal halide perovskites have recently attracted enormous interest in the field of resistive switching memories owing to their unique electrical properties. Unfortunately, two challenges, the inadequate long-term stability and the toxicity of lead, largely hinder their further practical application. Herein, a 1D all-inorganic lead-free CsCu2Br3 perovskite is proposed for resistive switching devices to resolve these issues. The CsCu2Br3-based resistive switching devices exhibit typical bipolar resistive switching behavior with low set voltage, high on/off ratio (103), stable retention properties (>2 × 104 s), and endurance (200 cycles) in air. The unencapsulated CsCu2Br3-based device still maintains resistive switching characteristics while stored in ambient environment for over 2 months. Moreover, four on-state multilevel information storage behavior has been observed by regulating the value of compliance current during set process. The resistive switching behavior is dominated by the formation and fracture of conductive filaments, which are induced by the movement of Br− ions under electrical bias. This work offers the opportunity and strategy for the design of air-stable and environment-friendly metal halide perovskite-based memory devices.

Metal Halide Perovskite Photo-Field-Effect Transistors with Chiral Selectivity.

Organic-inorganic (hybrid) metal halide perovskites (MHPs) incorporating chiral organic ligand molecules are naturally sensitive to left- and right-handed circular polarized light, potentially enabling selective circular polarized photodetection. Here, the photoresponses in chiral MHP polycrystalline thin films made of ((S)-(-)-α-methyl benzylamine)2PbI4 and ((R)-(+)-α-methyl benzylamine)2PbI4, denoted as (S-MBA)2 PbI4 and (R-MBA)2PbI4, respectively, are investigated by employing a thin-film field-effect transistor (FET) configuration. The left-hand-sensitive films made of (S-MBA)2PbI4 perovskite show higher photocurrent under left-handed circularly polarized (LCP) light than under right-handed circularly polarized (RCP) illumination under otherwise identical conditions. Conversely, the right-hand-sensitive films made of (R-MBA)2PbI4 are more sensitive to RCP than LCP illumination over a wide temperature range of 77-300 K. Furthermore, based on FET measurements, we found evidence of two different carrier transport mechanisms with two distinct activation energies in the 77-260 and 280-300 K temperature ranges, respectively. In the former temperature range, shallow traps are dominant in the perovskite film, which are filled by thermally activated carriers with increasing temperature; in the latter temperature range, deep traps with one order of magnitude larger activation energy dominate. Both types of chiral MHPs show intrinsic p-type carrier transport behavior regardless of the handedness (S or R) of these materials. The optimal carrier mobility for both handedness of material is around (2.7 ± 0.2) × 10-7 cm2 V-1 s-1 at 270-280 K, which is two magnitudes larger than those reported in nonchiral perovskite MAPbI3 polycrystalline thin films. These findings suggest that chiral MHPs can be an excellent candidate for selective circular polarized photodetection applications, without additional polarizing optical components, enabling simplified construction of detection systems.

Perspective on machine learning based investigated materials to realize Stable-Efficient-Toxin free (S-E-T) perovskite solar cells

The progress of third generation hybrid organic–inorganic metal-halide Perovskite Solar cells, widely-opened new doors for the researchers globally. The benefits of Perovskite Solar cells (PSC) such as high light absorption coefficient, easy preparation and low cost makes it the best in purpose at marketing level, but challenges on improving stability of the Perovskite solar cell makes it the secondary option compared to the conventional solar cells. Theimproved rate of change of power conversion efficiency (PCE) from 3.8 % (year 2009) to 22.1% (year 2016) to above 25% in 2022, made perovskitesolar cells the prominent choice for switching from conventional solar cells to new generation solar cells. In this paper, we condense the studies of ML investigated PSC’s over the past decade, for realizingmaterials that produceStable-Efficient- Toxin free (S-E-T) PSC. Some of the most applicable combinations of PSC’s are discussed that can be fabricated to verify the end-results with ML investigations.

Synthesizing and characterization of Lead Halide Perovskite Nanocrystals solar cells from reused car batteries

With the rapid increase of efficiency up to 23.7% during the past few years, hybrid organic-inorganic metal halide perovskite solar cells (PSCs) have become a research “hot spot” for many solar cell researchers. The perovskite materials show various advantages due to unique characteristics of perovskite materials, such as high photo-to-electric conversion efficiency, direct band gap, high light absorption coefficient, high charge-carrier mobility and long electron-hole electron transport distance. The low-cost fabrication techniques together with the high efficiency makes PSCs comparable with Si-based solar cells. This paper begins with the discussion of crystal structures of perovskite based on recent research findings. The following part of this paper discussion of synthetic process of lead iodide perovskite materials from lead-acid battery and Harvesting material from the anodes and cathodes of car battery; synthesizing PbI2 from the collected materials and compare with pure Lead iodide to know the absolute by XRD peak, depositing lead iodide perovskite nanocrystals. Efficient flexible PSCs are fabricated onto FTO glass substrate by a two-step coating method under ambient condition. By adjusting the concentration of precursor CH3NH3I (MAI), the morphology and thickness of perovskite layer is effectively tailored, according to SEM analysis and using TiO2 as electron transport layer instead of ZnO and CuI instead of spiro-OMeTAD as hole transport layer.

Achieving a Highly Stable Perovskite Photodetector with a Long Lifetime Fabricated via an All-Vacuum Deposition Process

Hybrid organic-inorganic metal halide perovskites (HOIP) have become a promising visible light sensing material due to their excellent optoelectronic characteristics. Despite the superiority, overcoming the stability issue for commercialization remains a challenge. Herein, an extremely stable photodetector was demonstrated and fabricated with Cs0.06FA0.94Pb(I0.68Br0.32)3 perovskite by an all-vacuum process. The photodetector achieves a current density up to 1.793 × 10-2 A cm-2 under standard one sun solar illumination while maintaining a current density as low as 8.627 × 10-10 A cm-2 at zero bias voltage. The linear dynamic range (LDR) and transient voltage response were found to be comparable to the silicon-based photodetector (Newport 818-SL). Most importantly, the device maintains 95% of the initial performance after 960 h of incessant exposure under one sun solar illumination. The achievements of these outstanding results contributed to the all-vacuum deposition process delivering a film with high stability and good uniformity, which in turn delays the degradation process. The degradation mechanism is further investigated by impedance spectroscopy to reveal the charge dynamics in the photodetector under different exposure times.

Role of surface terminations in the chemical stability of CH3NH3PbI3 perovskite in combined light, H2O, and O2 environments: DFT/AIMD calculations and experimental validation

A deep understanding of the relationship between the surface termination of organic-inorganic metal halide perovskites and their structural degradation caused by environmental stimuli is critical for increasing the practicability of perovskite-based photovoltaic devices. In this work, the role of different surface termination on the degradation of CH3NH3PbI3 (MAPbI3) perovskite upon simultaneous exposure to water and oxygen in the presence of light is systematically investigated using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations methods. Our results show that photogenerated electrons increase the interaction of H2O and O2 molecules on the MAPbI3 perovskite and the coexistence of H2O and O2 molecules degrade the MAPbI3 perovskite surface faster than the presence of either monomer on the surface. AIMD results indicate that the PbI2-terminated MAPbI3 surface undergoes significant structural degradation upon simultaneous exposure to light, H2O, and O2, whereas the MAI-terminated surface is stable. Furthermore, a series of MAPbI3-based perovskite solar cells (PSCs) with different concentrations of MAI precursor are fabricated, and their photovoltaic performance is studied. Our experimental results show that the PSC treated with 3 mg mL−1 of MAI has achieved a maximum PCE of 16.16% and a larger VOC of 1.02 V, with correspondingly improved stability. The finding presented here provides a strategy for improving the quality of the MAPbI3 perovskite layer and its photovoltaic performance.

Implications of Electron Transport Layer and Back Metal Contact Variations in Tin–Lead Perovskite Solar Cells Assessed by Spectroscopic Ellipsometry and External Quantum Efficiency

The structural and optical properties of hybrid organic-inorganic metal halide perovskite solar cells are measured by spectroscopic ellipsometry to reveal an optically distinct interfacial layer among the back contact metal, charge transport, and absorber layers. Understanding how this interfacial layer impacts performance is essential for developing higher performing solar cells. This interfacial layer is modeled by Bruggeman effective medium approximations (EMAs) to contain perovskite, C60, BCP, and metal. External quantum efficiency (EQE) simulations that consider scattering, electronic losses, and the formation of nonparallel interfaces are created with input derived from ellipsometry structural-optical models and compared with experimental EQE to estimate optical losses. This nonplanar interface causes optical losses in short circuit current density (JSC) of up to 1.2 mA cm-2. A study of glass/C60/SnO2/Ag or Cu and glass/C60/BCP/Ag film stacks shows that C60 and BCP mix, but replacing BCP with SnO2 can prevent mixing between the ETLs to prevent contact between C60 and back contact metal and enable the formation of a planar interface between ETLs and back contact metals.

Synthesis, crystal structure and optical properties of the quasi-0D lead-free organic-inorganic hybrid crystal (C6H14N)3Bi2I9·H2O

The organic-inorganic metal halide perovskite materials have remarkable semiconductor and light absorption characteristics. It shows excellent application prospects in the fields of optoelectronics and temperature sensors. In this work, zero-dimensional lead-free (C6H14N)3Bi2I9·H2O single crystals were synthesized by conventional solvothermal reaction. The crystal structure was analyzed using single crystal X-ray diffraction (SXRD). (C6H14N)3Bi2I9·H2O was crystallized in the orthorhombic crystal system with the space group Pmn21. The material is stable for long-term storage under ambient conditions and shows a reversible thermochromic phenomenon. Through ultraviolet–visible–near-infrared (UV–vis–NIR) absorption analysis, the band gap of (C6H14N)3Bi2I9·H2O at room temperature is found to be 2.12 ​eV and it gradually decreases as the temperature increases. This indicates that the thermochromism is probably caused by charge transfer. The response of material to optical signals was also studied and the maximum value of the responsivity (R) and external quantum efficiency (EQE) at 275 ​nm could reach 11 ​mA/W and 2.4%, respectively. It suggests that the material has a potential for applications in photovoltaic devices.

Giant Humidity Effect of 2D Perovskite on Paper Substrate: Optoelectronic Performance and Mechanical Flexibility

AbstractFlexible optoelectronic devices have attracted enormous attention as an essential component in next‐generation wearable devices. To meet the trend of biocompatibility, flexibility and low cost, paper‐based optoelectronic devices have become compelling candidates. Moreover, 2D organic–inorganic metal halide perovskites have been extensively studied for the application in flexible optoelectronic devices owing to their long‐term moisture stability, optoelectronic tunability, and multiple quantum well (MQW) structures. Herein, the paper‐based flexible optoelectronic devices are designed by spin‐coating PEDOT:PSS and (iso‐BA)2MAn‐1PbnI3n+1 (n ≥ 1) on regular filter paper with responsivity of 2.62 mA W−1 and response time (τrise/τdecay) of 0.81/0.18 s at 35% relative humidity (RH). Furthermore, the responsivity may be increased by 250% within the humidity range from 35% to 90%, and remains above 92% of the initial value after measured for 1800 s at 60% RH. This work can pave the way for further studies about the humidity effect on perovskites for next‐generation green wearable electronics.