Organic-inorganic Thin Films Research Articles

From molecules to materials: SHG-CD microscopy of structured chiral films

The interplay between molecular and structural chirality as a function of local sample morphology determines the nonlinear optical properties of many organic and hybrid organic–inorganic thin films. Here, we used second harmonic generation circular dichroism (SHG-CD) microscopy of thin molecular films of 1,1′-bi-2-naphthol (R-BINOL) as a research model. Our results show that the SHG signal measured at frequencies close to the electronic transition of BINOL molecules is resonantly enhanced by more than an order of magnitude compared to the non-resonant case. The extracted resonant SHG-CD signal is dominated by the chiral response of the molecule. In contrast, structural chirality determines the non-resonant SHG-CD images. We see clear evidence that the interference of the SHG signals caused by the molecular and structural chirality can lead to a decrease in the overall SHG intensity when both SHG signals are out of phase. These findings highlight the intricate relationship between molecular and structural chirality on the one hand and structural morphology on the other hand and pave the way for novel applications by exploiting the chiroptic properties of thin films.

Synthesis, crystal structure, thermal stability, and photovoltaic properties of organic-inorganic hybridized copper-based perovskite single crystals modulated by organics

Organic-inorganic hybridized perovskite have excellent photovoltaic properties, especially Pb-based organic-inorganic perovskite polycrystalline thin films based on Pb-based organic-inorganic perovskite have achieved high power conversion efficiency, but the polycrystalline materials have a large number of grain boundaries and defects, which are susceptible to the influence of water and oxygen, leading to structural degradation, poor stability, high toxicity and slow degradation, which are not friendly to the environment. Therefore, in this paper, two copper-based organic-inorganic hybrid perovskite single crystals (C6H9N2)2CuCl4 and (C6H18N2)2Cu2Cl8 were synthesized by using the method of organic modulation, and were investigated by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis, and UV–vis diffuse reflectance spectroscopy. The samples were analyzed in detail for crystal structure, chemical groups, bond characterization, optical and thermal stability. The results show that (C6H9N2)2CuCl4 and (C6H18N2)2Cu2Cl8 single crystals belong to the C2/c space group of the monoclinic crystal system and the P-1 space group of the triclinic crystal system, respectively. The optical band gap of (C6H9N2)2CuCl4 is 2.45 eV, which is stable up to 179 °C, and that of (C6H18N2)2Cu2Cl8 is 2.47 eV, which is stable up to 163 °C. The thermal stability of the crystals can be regulated by changing the organic cation in the A-site, but the optical band gap of the crystals cannot be regulated significantly.

Topography and Nonlinear Optical Properties of Thin Films Containing Iodide-Based Hybrid Perovskites.

This article covers selected properties of organic-inorganic thin films of hybrid perovskites with the summary formulas CH3NH3MI3, where M = Pb, Cd, Ge, Sn, Zn. The paper discusses not only the history, general structure, applications of perovskites and the basics of the theory of nonlinear optics, but also the results of experimental research on their structural, spectroscopic, and nonlinear optical properties. The samples used in all presented studies were prepared in the physical vapor deposition process by using co-deposition from two independent thermal sources containing the organic and inorganic parts of individual perovskites. Ultimately, thin layers with a thickness of the order of nanometers were obtained on glass and crystalline substrates. Their structural properties were characterized by atomic force microscopy imaging. Spectroscopic tests were used to confirm the tested films' transmission quality and determine previously unknown physical parameters, such as the absorption coefficient and refractive index. Experimental results of the nonlinear optical properties were obtained by studying the second and third harmonic generation processes and using initial sample polarization in the so-called Corona poling process. The obtained experimental results allowed us to determine the second- and third-order nonlinear optical susceptibility of the tested materials.

Investigation of the stability of organic-inorganic halide perovskite thin films: Insight from experimental and simulation

Herein, we investigated the stability of lead halide perovskites under ambient conditions after mixing the two cations Formamidinium (FA) and Cesium (Cs). The CsxFA1-xPbI3 perovskites solutions were prepared with different contents of x (0.0, 0.3, 0.5, 0.7 and 1.0) and deposited on substrates by spin-coating technique. The CsxFA1-xPbI3 films were, afterwards, characterized using the X-ray diffraction (XRD), UV–visible spectroscopy, photoluminescence (PL) spectra and scanning electron microscopy (SEM) to figure out their crystallinity, morphology, and optical properties. We noticed a stable perovskite structure for the mixed compounds unalike the pure FA and Cs films. The XRD analysis revealed, even after two weeks, the growth and good stability after two weeks of the desired black cubic α-phase perovskite structure in opposite to FAPbI3 and CsPbI3 which, respectively, showed faster degradation and transition into non-perovskite δ-phase and ɣ-phase no perovskite phases. The mixed perovskites Cs-FA also displayed a high absorbance especially for the ones with 30% of Cs and 70% of FA or 50% of each, with an excellent band gap energy ranging between 1.52 and 1.7 eV where FAPbI3 and CsPbI3 were showing a bandgap between 1.5 and 1.9 eV respectively. Moreover, the performance of the CsxFA1-xPbI3 based solar cells were simulated with SCAPS by using the band gaps obtained from the experimental study and after by varying the band gap, the thickness of the absorber layers and then different types of Electron Transport Layer (ETL). The simulation results revealed that the Cs0.3FA0.7PbI3 based solar cells had the highest higher efficiency around 22.36%.

Surface engineering of lead-free two-dimensional organic-inorganic hybrid perovskite by laser interference lithography

Laser interference patterning of environment-friendly material with micro/nanoscale surface structures is in high demand for applications. We demonstrated the fabrication of periodic structure in copper-based organic-inorganic hybrid perovskite thin film by 532 nm laser two-beam interference. The extinction coefficient and index of refraction of the copper-based perovskite thin film were characterized by spectroscopic ellipsometry. The morphology of laser-induced structure was investigated by a combination of optical microscopy, scanning electron microscopy, and atomic force microscopy. In addition, the mechanism of the interaction between laser and copper-based perovskite thin film was discussed. This investigation expands the materials selection in laser fabrication and paves the way for optimization towards obtaining micro/nano features for applications in diffractive optics.

Understanding the Effects of Primary and Secondary Doping via Post‐Treatment of P‐Type and N‐Type Hybrid Organic–Inorganic Thin Film Thermoelectric Materials

AbstractHybrid organic/inorganic materials have emerged as promising thermoelectric (TE) materials since they inherit the individual strengths of each component, enabling rational materials design with enhanced TE performance. The doping of hybrid TE materials via post‐treatment processes is used to improve their performance, but there is still an incomplete understanding of the elicited effects. Here, the impact of different doping methods on the thin film TE performance of p‐type Te/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and n‐type Ag2Te/PEDOT:PSS hybrid materials is investigated. Primary doping through acid–base and charge transfer processes using H2SO4 and tetrakis(dimethylamino)ethylene, respectively, and the effects of secondary doping using ethylene glycol is examined. Through a combination of Hall effect measurements, hard X‐ray photoelectron spectroscopy, and Raman spectroscopy, variations in the charge carrier concentration, mobility, and overall TE performance are related to the morphological and chemical structure of the hybrid materials. This study provides an improved understanding of the effects that different post‐treatments have on hybrid materials and shows that the impact of these post‐treatments on pure PEDOT:PSS does not always apply to hybrid systems. These new insights into post‐treatment effects on hybrid materials is expected to facilitate further enhancement of their performance as electronic materials in general and thermoelectric materials in particular.

Orientation control of two-dimensional perovskite (CH3(CH2)3NH3)2(CH3NH3) n−1PbnI3n+1 (n = 2) thin films by thermal annealing

It has been attempted to preferentially orientate Pb-I layers in two-dimensional (2D) organic-inorganic hybrid perovskite thin films (CH3(CH2)3NH3)2(CH3NH3)Pb2I7 perpendicular to substrates only by thermal annealing after spin coating of a reagent solution for improvements in the energy-conversion-efficiency of solar cells. It is found from X-ray diffraction measurements that the ratio of diffraction intensity from the (202) plane to that from the (060) plane becomes larger in thermally annealed (50 °C–135 °C) samples. This indicates that the Pb-I layer tends to grow perpendicular to the surface of the substrate. In particular, the ratio has reached 8.2, which is larger compared with the ratio of 2.7 for the randomly oriented powder sample, for the sample prepared on SnO2 substrates. Such (202) oriented films seem to contribute to improvements in the energy-conversion-efficiency of tandem-type solar cells utilizing the 2D perovskite thin films as an active layer of the top cell.

Surface Characterization of the Solution‐Processed Organic–Inorganic Hybrid Perovskite Thin Films

The surface properties of organic-inorganic hybrid perovskites can strongly affect the efficiency and stability of corresponding devices. Even though different surface passivation methods are developed, the microscopic structures of solution-processed perovskite film surfaces are not systematically studied. This study uses low-temperature scanning tunneling microscopy to study the organic-inorganic hybrid perovskite thin films, MA0.4 FA0.6 PbI3 and MAPbI3 , synthesized by the spin-coating method.Flat surface structures, atomic steps, and crystal grain boundaries are resolved at an atomic resolution. The surface imperfections are also characterized, as well as the dominant defects.Simulations on different types of iodine vacancy configurations are performed by density functional theory calculations.In addition, it is observed that the surface iodine lattice structure is unstable during scanning. Tip scanning can also cause the vertical migration of surface iodine ions. The measurements provide the direct visualizations of the surface imperfections of the solution-processed perovskite films. They are essential for understanding the surface-related optoelectronic effects and rationally designing more efficient surface passivation methods.

Atomic and Molecular Layer Deposition of Chiral Thin Films Showing up to 99% Spin Selective Transport.

Spin electronics is delivering a much desired combination of properties such as high speed, low power, and high device densities for the next generation of memory devices. Utilizing chiral-induced spin selectivity (CISS) effect is a promising path toward efficient and simple spintronic devices. To be compatible with state-of-the-art integrated circuits manufacturing methodologies, vapor phase methodologies for deposition of spin filtering layers are needed. Here, we present vapor phase deposition of hybrid organic-inorganic thin films with embedded chirality. The deposition scheme relies on a combination of atomic and molecular layer deposition (A/MLD) utilizing enantiomeric pure alaninol molecular precursors combined with trimethyl aluminum (TMA) and water. The A/MLD deposition method deliver highly conformal thin films allowing the fabrication of several types of nanometric scale spintronic devices. The devices showed high spin polarization (close to 100%) for 5 nm thick spin filter layer deposited by A/MLD. The procedure is compatible with common device processing methodologies.

Photocatalytic Activity in the In-Flow Degradation of NO on Porous TiO2–Coated Glasses from Hybrid Inorganic–Organic Thin Films Prepared by a Combined ALD/MLD Deposition Strategy

A combined ALD/MLD (where ALD and MLD stand for atomic and molecular layer deposition, respectively) deposition strategy using TiCl4, H2O and HQ (hydroquinone) as precursors has been applied for the preparation of inorganic–organic thin films on soda-lime glasses. The alternate deposition of TiO2 layers, by pulsing TiCl4/H2O (ALD), and hybrid layers, using TiCl4/HQ (MLD), results in the formation of thin films that are precursors for porous TiO2-coatings after removal of the HQ template by annealing. The coated-glassed show good photocatalytic activity in the degradation of NO with up to 15% reduction of NO concentration in three successive photocatalytic cycles of 5 h each. Surface Scanning Electron Microscopy (SEM) images show that the TiO2-coating is composed of large grains that are made up of finer subgrains resulting in a porous structure with an average pore size of 3–4 nm. Transmission Electron Microscopy (TEM) images show two regions, a porous columnar structure on top and a denser region over the glass substrate. Energy Dispersive X-Ray (EDX) analysis, nanocrystal electron diffraction and Raman spectroscopy confirm the presence of the anatase phase, which, together with the porosity of the material, accounts for the observed photocatalytic activity.

Contact Printing of Multilayered Thin Films with Shape Memory Polymers.

This study describes a method for transfer printing microarrays of multilayered organic–inorganic thin films using shape memory printing stamps and microstructured donor substrates. By applying the films on the microstructured donor substrates during physical vapor deposition and modulating the interfacial adhesion using a shape memory elastomer during printing, this method achieves (1) high lateral and feature-edge resolution and (2) high transfer efficiency from the donor to the receiver substrate. For demonstration, polyurethane-acrylate stamps and silicon/silicon oxide donor substrates were used in the large-area transfer printing of organic–inorganic thin-film stacks with micrometer lateral dimensions and sub-200 nm thickness.

Tunable strongly interacting dipolar excitons in hybrid perovskites

We study theoretically the excitonic nonlinearity in hybrid organic-inorganic Ruddlesden-Popper perovskite thin films. The composite layered structure of these materials allows for flexible modulation of their excitonic response between the limiting cases of single atomic layer and wide quasi-two-dimensional quantum well. In particular, we demonstrate that transverse electric field leads to the spatial separation of charge carriers within the inorganic layer, giving rise to strongly interacting excitons possessing built-in dipole moment. Combined with exciton binding energy of the order of hundreds of meVs, this makes hybrid perovskites an optimal platform for tailoring of nonlinear optical response at reduced dimensionality.

Growth of Hybrid Perovskite Films via Single-Source Perovskite Nanoparticle Evaporation.

Herein, we demonstrate a vacuum-based evaporation approach to fabricate organic-inorganic perovskite thin films by using phase-formed halide perovskite nanoparticles (NPs) as a precursor/source. We are able to consistently obtain MAPbX3 (MA=CH3 NH3 and X=Cl, Br or I) thin films at various substrates (e. g., glass, ITO, or plastic). The perovskite phase formation in thin film form is confirmed by x-ray diffraction (XRD) studies. Small micro-strain (tensile) values of 1.64×10-3 , 1.42×10-3 and 6.85×10-4 obtained for MAPbCl3 , MAPbBr3 and MAPbI3 films respectively from Williamson-Hall equation indicate low structural distortions in perovskite thin films. The absorption spectra of thin films show sharp band edge having direct band gap, which is followed by narrow full width at half maxima (FWHM ∼0.1 eV) of the emission peak. Thin films of MAPbCl3 , MAPbBr3 and MAPbI3 show direct band gap of 3.1 eV, 2.4 eV and 1.6 eV, respectively. Small Urbach energy values of 33 meV, 44 meV and 66 meV for MAPbCl3 , MAPbBr3 and MAPbI3 films respectively indicates low defect density in various perovskite films. Scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDS) shows high surface coverage and uniform chemical composition of MAPbX3 (X=Cl, Br and I) thin films deposited by the present method. We have successfully controlled the film thickness from 250 nm to 1 μm by varying the nanoparticle precursor amount. The perovskite thin films deposited by the present method are highly stable against the degradation under ambient conditions. Systematic XRD studies along with absorption data demonstrate that the MAPbCl3 and MAPbBr3 films stored under ambient conditions remained stable for more than 30 days and MAPbI3 films for more than 7 days.

Ultrasensitive organic-inorganic nanotube thin films of halogenated perovskites as room temperature ammonia sensors

Recently organic-inorganic halide perovskites like MAPbX3 (XBr, Cl, I), are being investigated as a substitute to commonly used metal oxide semiconductor-based sensors for the detection of various volatile organic compounds and toxic gases at room temperature. The present work provides detailed insights into chlorine halide incorporation on the ammonia sensing performance of the most popular MAPbI3 (MAPI) perovskite thin films. Here, we shown that the MAPbI3−xClx (MAPIC) sensor exhibits a high response of 591%, nearly13 times larger than the MAPI sensor for 10 ppm of ammonia exposure at room temperature. This work demonstrates excellent potential of MAPIC as an ultra-sensitive, stable and reversible NH3 sensor vis-à-vis MAPI sensor for early detection of NH3. The proposed sensing mechanism suggests that by engineering the morphology at the nanoscale and doping induced excellent charge carrier diffusion length could enhance ammonia sensor responsivity.

Atomic/molecular layer deposition of Ti-organic thin films from different aromatic alcohol and amine precursors

Atomic/molecular layer deposition (ALD/MLD) processes based on TiCl4 as the metal source, and hydroquinone (HQ), 4-aminophenol (AP), p-phenylenediamine (PDA) or 4,4′-oxydianiline (ODA) as the organic precursor are systematically investigated to shed light on the factors affecting the inorganic-organic thin film growth. All the four ALD/MLD processes yield amorphous Ti-organic thin films which are here characterized by ex-situ X-ray reflectivity and Fourier transform infrared measurements for the film thickness and bonding scheme. First principles modelling results are presented to explore differences in the interaction of organic precursors with surface-bound TiCl4. For the TiCl4+AP process the high growth rate achieved, i.e. ca. 10 Å per one ALD/MLD cycle, essentially corresponds to the ideal thickness of the [Ti-O-C6H4N-Ti] building unit. For both the ODA- and PDA-based processes the growth rates are considerably lower, while the TiCl4+HQ process yields the hybrid film with an intermediate growth rate. We attribute these observations to (i) the higher reactivity of the OH groups in comparison to the NH2 groups towards TiCl4, and (ii) the higher tendency of a heterobifunctional organic precursor to orientate vertically and avoid unwanted double reactions on the surface.

Thermal Transport in Engineered Hybrid Organic–Inorganic Perovskite Metasurfaces

Halide perovskites have recently gained widespread attention for their exceptional optoelectronic properties which have been illuminated by extensive spectroscopic investigations. In this article, nanophotonic surface-engineering using soft-lithography has been used to reproduce nanostructures with enhanced functionalities. A non-invasive optical technique based on Raman and photolumines-cence (PL) spectroscopy is employed to investigate the interactive effect of the thermal and optical behaviour in surface-patterned hybrid organic-inorganic halide perovskite thin films. The thermophys-ical properties of the engineered perovskite films are extracted from the softening of the representa-tive peak positions in the Raman and PL spectra of the samples which act as temperature markers. The investigation suggests a comparatively higher rise in the local temperature for the patterned thin films resulting from their enhanced absorption. Therefore, a cross-talk between the opto-thermal transport phenomena in imprinted perovskite thin films pertaining to both enhancing device properties along with maintaining device stability is established.

New Hybrid Organic-Inorganic Thin Films by Molecular Layer Deposition for Rechargeable Batteries

The design of multifunctional thin films holds the key to manipulate the surface and interface structure of the electrode and electrolyte in rechargeable batteries and achieve desirable performance for various applications. Molecular layer deposition (MLD) is an emerging thin-film technique with exclusive advantages of depositing hybrid organic-inorganic materials at a nanoscale level and with well tunable and unique properties that conventional thin films might not have. Herein, we provide a timely mini-review on the most recent progress in the surface chemistry and MLD process of novel hybrid organic-inorganic thin films and their applications as the anode, cathode, and solid electrolytes in lithium-ion batteries. Perspectives for future research in designing new MLD process and precursors, enriching MLD material library, and expanding their potential applications in other energy storage systems, are discussed at the end.

Performance Investigation of a Perovskite Solar Cell with TiO2 and One Dimensional ZnO Nanorods as Electron Transport Layers

Organic-inorganic halide perovskite thin film perovskite solar cells are gaining much attention, in recent years. Designing proper electron transport layer (ETL) and hole transport layer (HTL) with high quality to achieve devices with higher efficiency are fundamental. One dimensional (1D) nanostructures are newly introduced materials with high mobility and low recombination rate, which may improve the device performance. In this paper, 1D ZnO nanorods (ZnO-NRs) as well as planar TiO2 are considered as the ETL of the device and their electrical performance are compared with different HTL materials in Sn- and Pb- perovskite. In addition, impact of critical design parameters including absorber thickness, interface defect density, back contact electrode materials on the performance of the device are comprehensively assessed. In this work, the simulations have been carries out using a 1D Solar Cell Capacitance Simulator (SCAPS-1D). The results show that in Sn- perovskite, ZnO-NRs has superior performance in comparison with TiO2 with maximum photon conversion efficiency (PCE) of 16.7 % and short circuit current density of 30.21(mA/cm2). However, in terms of Pb-perovskite planar TiO2 has given the best performance with PCE of 19.6%. The results in this paper pave the way for introducing inexpensive high performance solar cell.

High-performance methylammonium-free ideal-band-gap perovskite solar cells

Summary The development of mixed tin-lead (Sn-Pb)-based perovskite solar cells (PSCs) with low band gap (1.2–1.4 eV) has become critical not only for pushing single-junction devices toward the maximum efficiency given by the Shockley-Queisser limit, but also for enabling all-perovskite tandem devices beyond this limit. However, achieving high power-conversion efficiency (PCE) and long-term device operation stability simultaneously remains a significant challenge for Sn-Pb-based PSCs. Here, we demonstrate near ideal-band-gap (∼1.34 eV) methylammonium-free Sn-Pb-based PSCs with high efficiency (∼20%) and promising operational stability of maintaining >80% of initial PCE over 750 h under maximum-power-point tracking. The key to this success is the use of a SnCl2⋅3FACl complex additive that improves the microstructure and reduces the development of residual stress in the Sn-Pb perovskite thin films, which in turn enhances the efficiency and stability of the Sn-Pb-based ideal-band-gap PSCs.

Surface lattice engineering through three-dimensional lead iodide perovskitoid for high-performance perovskite solar cells

<h2>Summary</h2> Surface modification of organic-inorganic halide perovskite thin films represents a promising approach to enhance the efficiency and stability of perovskite solar cells. Here, we synthesized <i>N</i>-methyl-1,3-propane diammonium diiodide (Me-PDAI₂) and found that Me-PDA²⁺ can template a three-dimensional "perovskitoid" structure (Me-PDA)Pb₂I₆. Simple surface treatment with Me-PDAI₂ on top of a standard (FAPbI₃)_0.85(MAPbI₂Br)_0.10(CsPbI₃)_0.05 perovskite induces the formation of a thin (Me-PDA)Pb₂I₆ perovskitoid surface layer, leading to smoother surface texture, longer charge-carrier lifetime, higher charge-carrier mobility, and a reduced surface-defect density. With the perovskitoid surface modification, the device efficiency is significantly improved from 20.3% to 22.0% along with enhanced stability in both shelf life (ISOS-D-1 stability) and operation (ISOS-L-1 stability). We further demonstrated that the perovskitoid surface engineering approach is applicable to various perovskite compositions, including CsFAMA-, FAMA-, and MA-based lead halide perovskites, making perovskitoid an important design motif for perovskite surface engineering for enhanced device performance and stability.