Organolead Halide Perovskite Research Articles

Controlling the transformation of intermediate phase under near-room temperature for improving the performance of perovskite solar cells

Perovskite crystallizations under different temperature phases have tremendously effects on the performance of perovskite solar cells. Here, we report an effective near-room-temperature fabrication technique to prepare high quality organolead halide perovskite films. By doping a certain amount of cesium cations into precursor solution, smooth and well-crystallized perovskite films with no other impurity phase can be obtained at an annealing temperature of 50 °C. This phenomenon can be interpreted as relatively low energy required for the diffusion of cesium cations into intermediate phase framework, promoting the removal of DMSO and subsequent diffusion of organic cations. Corresponding PSCs has been prepared based on this technique, and the highest PCE of 17.9% has been obtained with annealing temperature of only 50 °C. This work exhibits a well balance between reducing of annealing temperature and increase of device performance and is expected to broaden the range of choices for substrate materials.

Intrinsic White‐Light‐Emitting Metal–Organic Frameworks with Structurally Deformable Secondary Building Units

AbstractThe secondary building units in metal–organic frameworks (MOFs) are commonly well‐defined metal–oxo clusters or chains with very limited structural strain. Herein, the structurally deformable haloplumbate units that are often observed in organolead halide perovskites have been successfully incorporated into MOFs. The resultant materials are a rare class of isoreticular MOFs exhibiting large Stokes‐shifted broadband white‐light emission, which is probably induced by self‐trapped excitons from electron–phonon coupling in the deformable, zigzag [Pb2X3]+ (X=Cl, Br, or I) chains. In contrast, MOFs with highly symmetric, robust haloplumbate chains only exhibit narrow UV–blue photoemission. The designed MOF‐based intrinsic white‐light photoemitters have a number of advantages over hybrid inorganic–organic perovskites in terms of stability and tunability, including moisture resistance, facile functionalization of photoactive moieties onto the organic linkers, introduction of luminescent guests.

Intrinsic White-Light-Emitting Metal-Organic Frameworks with Structurally Deformable Secondary Building Units.

The secondary building units in metal-organic frameworks (MOFs) are commonly well-defined metal-oxo clusters or chains with very limited structural strain. Herein, the structurally deformable haloplumbate units that are often observed in organolead halide perovskites have been successfully incorporated into MOFs. The resultant materials are a rare class of isoreticular MOFs exhibiting large Stokes-shifted broadband white-light emission, which is probably induced by self-trapped excitons from electron-phonon coupling in the deformable, zigzag [Pb2 X3 ]+ (X=Cl, Br, or I) chains. In contrast, MOFs with highly symmetric, robust haloplumbate chains only exhibit narrow UV-blue photoemission. The designed MOF-based intrinsic white-light photoemitters have a number of advantages over hybrid inorganic-organic perovskites in terms of stability and tunability, including moisture resistance, facile functionalization of photoactive moieties onto the organic linkers, introduction of luminescent guests.

Pressure-Induced Optical Band Gap Transition in Methylammonium Lead Halide Perovskites

Organic–inorganic hybrid perovskites have attracted significant attention because of their distinguished optoelectronic properties, which can be applied in high-efficiency solar cells and light-emitting devices. A majority of the systematic studies on the regulation of the band gap in the family of organolead halide perovskites have focused on changing the compositions of halogens. However, mechanical compression provides a wider structural diversity without changing the composition. In this paper, fabrication of organic–inorganic hybrid perovskites (CH3NH3PbX3, X = Cl, Br, and I) is reported. The crystal structure, electronic properties, and optical band gap energies of the synthesized perovskites were investigated. Also, the effects of changing the external pressure on the band gap of CH3NH3PbX3, X = Cl, Br, and I were studied. The results indicate an important progress in tuning the band structure and optoelectronic properties of organometal halide perovskites via pressure engineering, which brings for...

Single-Particle Organolead Halide Perovskite Photoluminescence as a Probe for Surface Reaction Kinetics.

Photoluminescence (PL) of organolead halide perovskites (OHPs) is sensitive to OHPs' surface conditions and is an effective way to report surface states. Literature has reported that at the ensemble level, the PL of photoexcited OHP nanorods declines under an inert nitrogen (N2) atmosphere and recovers under subsequent exposure to oxygen (O2). At the single-particle level, we observed that OHP nanorods photoblink at rates dependent on both the excitation intensity and the O2 concentration. Combining the two sets of information with the charge-trapping/detrapping mechanism, we are able to quantitatively evaluate the interaction between a single surface defect and a single O2 molecule using a new kinetic model. The model predicts that the photodarkening of OHP nanorods in the N2 atmosphere has a different mechanism than conventional PL quenching, which we call photo-knockout. This model provides fundamental insights into the interactions of molecular O2 with OHP materials and helps design a suitable OHP interface for a variety of applications in photovoltaics and optoelectronics.

Electronic Structure of Nonionic Surfactant-Modified PEDOT:PSS and Its Application in Perovskite Solar Cells with Reduced Interface Recombination.

The interfacial properties of organolead halide perovskite solar cells (PSCs) affect the exciton and charge-transport dynamics significantly. Thus, proper modification of the interfaces between perovskite and charge-transport layers is an efficient method to increase the power conversion efficiency (PCE) of PSCs. In this work, we explore the effect of a nonionic surfactant, that is, Triton X-100 (TX) additive, in the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hole-transport layer. The electronic structure of TX-modified PEDOT:PSS is investigated with ultraviolet/X-ray photoelectron spectroscopy and X-ray absorption spectroscopy with various TX concentrations. The surface of the TX-modified PEDOT:PSS layer showed high TX content, and thus the semimetallic properties of PEDOT:PSS were suppressed conspicuously by its insulating nature. With the TX-modified PEDOT:PSS, the PCE of methylammonium lead iodide (MAPbI3) PSCs increased significantly. To elucidate the origin of the improved device performance, the electrical properties and photoluminescence were investigated comprehensively. Consequently, it was found that the TX additive inhibits interface recombination between PEDOT:PSS and MAPbI3, which is caused by the suppression of semimetallic properties of the PEDOT:PSS surface. Hence, we fabricated flexible PSCs successfully using a graphene electrode and TX-modified PEDOT:PSS.

Toward Ultrahigh Sensitivity and UV–Vis–NIR Broadband Response of Organolead Halide Perovskite/Tin–Phthalocyanine Heterostructured Photodetectors

Organolead halide perovskite has recently emerged as a star material for various photoelectronic devices owing to its excellent optical and electronic properties. However, it is challenging to develop a perovskite-based photodetector with response across the UV–vis–NIR spectrum due to the lack of absorption in the NIR region for perovskite materials. Herein, we report a broadband photodetector based on the MAPbI3/SnPc heterostructure with mutual-complementary absorption spectra, extending the photoresponse from UV–vis to the NIR region because of the dominant absorption of the SnPc. The ultralow dark current of ∼0.01 nA is obtained and the ultrahigh photosensitivity is up to 105, which is attributed to the high dark resistance and the high electron injection barrier of the heterostructure, and the enhanced photoresponse by the heterostructure architecture. The outstanding sensitivity of our broadband photodetector can be comparable or superior to that of some inorganic, organic, and perovskite photodetectors reported previously. This work provides a route to designing high-performance broadband photodetectors with low noise and high sensitivity.

In situ investigation of light soaking in organolead halide perovskite films

Organolead halide perovskite solar cells (PSCs) have generated extensive attention recently with power conversion efficiency (PCE) exceeding 23%. However, these PSCs exhibit photoinduced instability in the course of their current-voltage measurements. In this work, we study the light-induced behavior in CH3NH3PbI3−xClx films in situ, by employing wide-field photoluminescence (PL) microscopy to obtain both the spatially and temporally resolved PL images simultaneously. Along with the increase in the PL intensity under continuous illumination, some areas render PL inactive. By characterizing the excitation energy dependent long-time PL decay behavior, we suggest that the PL quenching can be ascribed to a localized accumulation of iodide ions driven by the optical field. This ion localization leads to an enhancement of non-radiative recombination. The appearance of the PL inactive areas in the perovskite film impedes its photovoltaic device performance approaching the theoretical maximum PCE. Therefore, the herein presented real-time investigation of the light soaking of perovskite films is a versatile and adaptable method providing more details to improve the performance of PSCs.

Quantitative chemical analysis of perovskite deposition using spin coating

Lead and halide ion compositions of spin coated organo-lead halide perovskite films have been quantified using ion chromatography (IC) and atomic absorption spectroscopy (AAS) using perovskite films manufactured by 5 different researchers (3 replicates per treatment) to monitor variability between researchers and individual researcher reproducibility. Planar and mesoporous TiO2-coated glass substrates have been studied along with tribromide (CH3NH3PbBr3), triiodide (CH3NH3PbI3) and mixed halide (CH3NH3PbI3−xClx) perovskite films. The data show low yields of spin coated perovskite material (ca. 1%) and preferential deposition of I− over Cl− in mixed halide films.

Organolead halide perovskite-based metal-oxide-semiconductor structure photodetectors achieving ultrahigh detectivity

Organolead halide perovskite with excellent optoelectronic properties, which endows its potential applications in versatile optoelectronic device including solar cells and photodetectors. In spite of great efforts made on the perovskite photodetectors, novel device configurations based on perovskite films have to be explored to further improve the performance. Here, we present perovskite photodetectors enabled by a novel metal (Al)–oxide–semiconductor (perovskite) (MOS) structure. The unique photodetector can work on a wide voltage range and exhibits extreme characteristics with a pA-scale dark current, and a high detectivity (>1014 Jones). Both ultralow dark and light currents enable the small power consumption output ∼nW under 2 mW cm−2 at 2 V. The C–V data analysis proves that the charge carriers are accumulated at the oxide/perovskite interface, which leads to the reduction of the conduct band offset. At a low voltage the current transport behaviors for the MOS structure photodetectors are dominated by the Ohm’s Law, while at a high voltage, the main mechanism is Schottky emission which is demonstrated by temperature-dependence I–V measurements. Our results strongly propose the use of perovskite based photodetectors with a unique MOS structure in the application of optoelectronic devices.

Numerical modeling of exciton impact in two crystalographic phases of the organo-lead halide perovskite (CH3NH3PbI3) solar cell

To improve the power conversion efficiency of solar cells based on organo–lead halide perovskites, a detailed understanding of the device physics is fundamental. Here, a computational analysis of excitons impact is reported for these types of photocell. Numerical calculations based on the model, which take into account electronic charge carriers (electrons and holes), excitons and ions, have been carried out. The role of excitons in two crystallographic phases associated with different temperatures (80 K and 295 K) have been studied with the Saha relation, which clearly distinguishes a domination of free charge carriers or excitons. We have confirmed that excitons prevail in the orthorombic phase. Our work provides information about the photophysics of the lead halide perovskite, which allows for a better understanding of the operation of devices based on perovskite materials.

Multi Band Gap Electronic Structure in CH3NH3PbI3

Organo-lead halide perovskite solar cells represent a revolutionary shift in solar photovoltaics, introducing relatively soft defect containing semiconductors as materials with excellent charge collection for both electrons and holes. Although they are based on the nominally simple cubic perovskite structure, these compounds are in fact very complex. For example, in (CH3NH3)PbI3 the dynamics and ensuing structural fluctuations associated with the (CH3NH3)+ ions and the interplay with the electronic properties are still not fully understood, despite extensive study. Here, using ab-initio calculations, we show that at room and higher temperature, the rotation of CH3NH3 molecules can be viewed as effectively giving local structures that are cubic and tetragonal like from the point of view of the PbI3 framework, though in fact having lower symmetry. Both of these structures are locally polar, with sizable polarization, ~10 μC/cm2 due to the dipoles on the organic. They become energetically degenerate in the volume range, V ~ 250 Å3/f.u–265 Å3/f.u. We also find very significant dependence of the band gap on the local structure. This type of transition is analogous to a transition between two ferroelectric structures, where in-spite of strong electron phonon coupling, there is strong screening of charged defects which can lead to enhanced mobility and charge collection. The results provide insights into the enhanced light absorption near the band edge and good charge collection in this material.

Conjugated Molecules “Bridge”: Functional Ligand toward Highly Efficient and Long‐Term Stable Perovskite Solar Cell

AbstractInterfacial ligand passivation engineering has recently been recognized as a promising avenue, contributing simultaneously to the optoelectronic characteristics and moisture/operation tolerance of perovskite solar cells. To further achieve a win‐win situation of both performance and stability, an innovative conjugated aniline modifier (3‐phenyl‐2‐propen‐1‐amine; PPEA) is explored to moderately tailor organolead halide perovskites films. Here, the conjugated PPEA presents both “quasi‐coplanar” rigid geometrical configuration and distinct electron delocalization characteristics. After a moderate treatment, a stronger dipole capping layer can be formed at the perovskite/transporting interface to achieve favorable banding alignment, thus enlarging the built‐in potential and promoting charge extraction. Meanwhile, a conjugated cation coordinated to the surface of the perovskite grains/units can form preferably ordered overlapping, not only passivating the surface defects but also providing a fast path for charge exchange. Benefiting from this, a ≈21% efficiency of the PPEA‐modified solar cell can be obtained, accompanied by long‐term stability (maintaining 90.2% of initial power conversion efficiency after 1000 h testing, 25 °C, and 40 ± 10 humidity). This innovative conjugated molecule “bridge” can also perform on a larger scale, with a performance of 18.43% at an area of 1.96 cm2.

Photonic Artificial Synapses: Photonic Organolead Halide Perovskite Artificial Synapse Capable of Accelerated Learning at Low Power Inspired by Dopamine‐Facilitated Synaptic Activity (Adv. Funct. Mater. 5/2019)

Photonic Artificial Synapses: Photonic Organolead Halide Perovskite Artificial Synapse Capable of Accelerated Learning at Low Power Inspired by Dopamine‐Facilitated Synaptic Activity (Adv. Funct. Mater. 5/2019)

Influence of the annealing temperature on the organometallic halide perovskite phase formation via CH3NH3Cl as additive in sequential deposition process

Abstract Organometallic halide perovskite materials with the general formula ABX3 have been recently interested as active layers in perovskite solar cells. It is well known that the O2 is the main problem for fabricated perovskite solar cells. Usually, the perovskite thin film need to be prepared in the N2 atmosphere or in the glove box. In this research, the metal halide perovskite CH3NH3PbI2Cl thin films were successfully deposited using spin-coating technique via a single step solution deposition and CH3NH3Cl as additive in sequential deposition process in the open air. The effect of annealing temperature on the organolead halide perovskite phase formation of CH3NH3PbI2Cl thin film was investigated. The phase formation as well as crystal structure were investigated by X-ray diffractometer, and we found that organolead halide perovskite thin film exhibited a pure phase perovskite without the unwanted phases. The crystallinity of the perovskite thin film was enhanced significantly by increasing the annealing temperature, and a single phase of the perovskite phase was observed by increment of the annealing temperature that is above 100OC. In addition to this, the growth of crystallinity in the halide perovskite thin film was increased with increasing heat treatment temperature. Furthermore, the morphology variation of the thin films were examined by Field Emission Scanning Electron Microscopy.

Highly stable enhanced near-infrared amplified spontaneous emission in solution-processed perovskite films by employing polymer and gold nanorods.

Solution-processed organo-lead halide perovskites have emerged as promising optical gain media for tunable coherent light sources. The lasing performance is generally determined by the as-synthesized crystal quality. Noble metal nanostructures have been widely utilized to enhance optical responses due to their unique property of localized surface plasmon resonance. Herein, we report a simple method to enhance the near-infrared amplified spontaneous emission (ASE) performance of MAPbI3 polycrystalline films by solution-processing a PMMA spacer layer and an Au NR-doped PMMA top layer on perovskite thin films. As a result, the ASE threshold of the triple-layer perovskite film was significantly reduced by around 36% and the ASE intensity increased by 13.9-fold, compared to the pristine film. The underlying mechanism was attributed to the combined effects of surface passivation by PMMA and plasmon resonance enhancement of Au NRs. The passivation effect results in suppressing the nonradiative recombination and prolonging excited state decay, which have been investigated by transient absorption and pump-probe measurements. The plasmon effect is systematically studied through distance-dependent and spectra-dependent plasmon enhanced emission. The perovskite films with PMMA and Au NR coating showed great stability for 180 min under intense pulse laser continuous irradiation. The improved ASE performance still remained after leaving the film under the atmosphere for more than one month. We have successfully demonstrated a highly stable and sustained ASE output from MAPbI3 films under pulse laser excitation. This study provides a general approach for exploring plasmonic nanostructures in combination with polymers in the development and application of low-cost solution-processed semiconductor lasers.

Tetradic phosphor white light with variable CCT and superlative CRI through organolead halide perovskite nanocrystals.

In this work, the emission spectral range of halide perovskite nanocrystals is extended from violet to infrared, the widest emission range for halide perovskites to date. This range extension was made possible by a cost-effective solution-based synthesis process that only involves two halides [MAPb(BrxI1−x)3 and MA = CH3NH3]. Furthermore, the correlated-color temperature (CCT) of white light is tuned by blending an appropriate fraction of the as-synthesized blue, green, yellow, and red emitting nanocrystals. This represents one of the first applications of a tetradic phosphor system for maximizing the color rendering index (CRI) for this material. The CCT ranges from warm to cool white (2759–6398 K) and the CRI has a maximum value of 93.95. Thus, this fourfold phosphor approach demonstrates that halide perovskites are promising alternatives to conventional phosphors in the search for low-cost and high-quality white light sources in the next generation of white lighting technology.

Ether‐Soluble Cu53 Nanoclusters as an Effective Precursor of High‐Quality CuI Films for Optoelectronic Applications

AbstractAn effective strategy is developed to synthesize high‐nuclearity Cu clusters, [Cu53(RCOO)10(C≡CtBu)20Cl2H18]+ (Cu53), which is the largest CuI/Cu0 cluster reported to date. Cu powder and Ph2SiH2 are employed as the reducing agents in the synthesis. As revealed by single‐crystal diffraction, Cu53 is arranged as a four‐concentric‐shell Cu3@Cu10Cl2@Cu20@Cu20 structure, possessing an atomic arrangement of concentric M12 icosahedral and M20 dodecahedral shells which popularly occurs in Au/Ag nanoclusters. Surprisingly, Cu53 can be dissolved in diethyl ether and spin coated to form uniform nanoclusters film on organolead halide perovskite. The cluster film can subsequently be converted into high‐quality CuI film via in situ iodination at room temperature. The as‐fabricated CuI film is an excellent hole‐transport layer for fabricating highly stable CuI‐based perovskite solar cells (PSCs) with 14.3 % of efficiency.

Ether-Soluble Cu53 Nanoclusters as an Effective Precursor of High-Quality CuI Films for Optoelectronic Applications.

An effective strategy is developed to synthesize high-nuclearity Cu clusters, [Cu53 (RCOO)10 (C≡CtBu)20 Cl2 H18 ]+ (Cu53 ), which is the largest CuI /Cu0 cluster reported to date. Cu powder and Ph2 SiH2 are employed as the reducing agents in the synthesis. As revealed by single-crystal diffraction, Cu53 is arranged as a four-concentric-shell Cu3 @Cu10 Cl2 @Cu20 @Cu20 structure, possessing an atomic arrangement of concentric M12 icosahedral and M20 dodecahedral shells which popularly occurs in Au/Ag nanoclusters. Surprisingly, Cu53 can be dissolved in diethyl ether and spin coated to form uniform nanoclusters film on organolead halide perovskite. The cluster film can subsequently be converted into high-quality CuI film via in situ iodination at room temperature. The as-fabricated CuI film is an excellent hole-transport layer for fabricating highly stable CuI-based perovskite solar cells (PSCs) with 14.3 % of efficiency.

Influence of the Iodide to Bromide Ratio on Crystallographic and Optoelectronic Properties of Rubidium Antimony Halide Perovskites

Rubidium antimony halides are a promising low toxic alternative to organo-lead halide perovskites as photovoltaic material. In this contribution, we systematically investigate the influence of vary...