xClx Films Research Articles

Enhanced optical and electronic properties of chlorobenzene-assisted perovskite CH3NH3PbI3−xClx film incorporated in p-i-n solar cells

Enhanced optical and electronic properties of chlorobenzene-assisted perovskite CH3NH3PbI3−xClx film incorporated in p-i-n solar cells

Enhanced efficiency, photocurrent and device stabilities of guanidinium chloride-based double cation mixed halide perovskite solar cells fabricated under humid conditions

Investigations on the guanidinium chloride-included double cation mixed halide (DCMH) perovskite solar cells (PSCs) at ambient condition were performed. A modified two-step vapour deposition technique was employed for the fabrication of guanidinium [GU; C(NH2)3]-incorporated methylammonium lead iodide (MAPI) under humid conditions (RH = 65–75%). The two-step deposition was performed via methylammonium iodide (MAI) vapour treatment on GUPbI3−xClx (x = 1) perovskite film. The X-ray diffraction (XRD) patterns indicate the presence of secondary peaks corresponding to GUPbI3−xClx (x = 1) along with MAPI, and the left-shift of the characteristic (110), (220) and (310) peaks confirmed the inclusion of GU cation. The MA-GUPbI3−xClx (x = 1) film showed better morphology, with smooth surface and large grain size (∼1 μm). The device characteristics showed that the two-step deposited MA-GUPbI3−xClx (x = 1) exhibited an efficiency of PCEmax = 17.03 ± 0.44% which was higher than the conventional MAPI (PCEmax = 15.64 ± 0.32). The photocurrent stability of the MA-GUPbI3−xClx (x = 1)-based PSC was found to be better than MAPI. The guanidinium included MAPI-based PSC retained around 90% of its pristine PCE after continuous illumination for 350 h, while the PCE of MAPI-based PSCs deteriorated with the illumination time.

Nonlinear optical response, theoretical efficiencies, and high photosensitivity of CH3NH3PbI3−xClx thin films for photonic applications

In this paper, we have investigated the nonlinear optical response and theoretical efficiency of CH3NH3PbI3−xClx thin films from the optical transmission and reflection measurements. The dispersion of the complex refractive index is evaluated using the Wemple–DiDomenico single oscillator model. The oscillator energy (E0) of CH3NH3PbI3−xClx follows by an empirical relationship with optical bandgap (Eg) as E0 ≈ 2.41 Eg for chemical dip coating, spray, and E0 ≈ 1.63 Eg for dipping deposited samples, respectively. The long wavelength refractive index, average oscillator wavelength, and oscillator strength are also determined using the Sellmeier oscillator equation. The estimated third-order nonlinear optical susceptibility is found to be the order of 10−12 esu. The incident photon and charge carrier interaction in CH3NH3PbI3−xClx is studied from the dielectric response of the samples. The charge carrier excitation is found higher at lower wavelength and experienced bulk excitation in volume while surface excitation on the surface region. The optical conductivity of CH3NH3PbI3−xClx is notably high, which leads to an increase in carrier transfer through the extrinsic halide perovskite material expedient for higher conversion efficiency. The highest theoretical efficiency of CH3NH3PbI3−xClx is estimated to be 17.4%, which is in excellent agreement with the experimental report. From photosensitivity study, it is confirmed that CH3NH3PbI3−xClx films are highly photosensitive. All these results comprehend that CH3NH3PbI3−xClx is a potential candidate for photonic applications.

Two-Dimensional Cs3Sb2I9-xClx Film with (201) Preferred Orientation for Efficient Perovskite Solar Cells.

All-inorganic Sb-perovskite has become a promising material for solar cell applications owing to its air stability and nontoxic lead-free constitution. However, the poor morphology and unexpected (001) orientation of Sb-based perovskite films strongly hinder the improvement of efficiency. In this work, two-dimensional Cs3Sb2ClxI9−x with (201) preferred orientation has been successfully fabricated by introducing thiourea (TU) to the precursor solution. The presence of the C=S functional group in TU regulates the crystallization dynamics of Cs3Sb2I9−xClx films and generates the (201) preferred orientation of Cs3Sb2ClxI9−x films, which could effectively improve the carrier transport and film morphology. As a result, the Cs3Sb2I9−xClx perovskite solar cells (PSCs) delivered a power conversion efficiency (PCE) of 2.22%. Moreover, after being stored in nitrogen at room temperature for 60 days, the devices retained above 87.69% of their original efficiency. This work demonstrates a potential pathway to achieve high-efficiency Sb-based PSCs.

In-Situ Nano-Auger Probe of Chloride-Ions during CH3NH3PbI3-xClx Perovskite Formation.

Organo-halide perovskite solar cells (PSCs) have emerged as next-generation photovoltaics, owing to their high power-conversion efficiency (PCE), lower production cost, and high flexibility. ABX3-structured methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3) perovskite is a widely studied light-absorbing material in PSCs. Interestingly, a small amount of chlorine incorporation into MAPbI3 increases charge carrier diffusion lengths (from 129 nm to 1069 nm), which enables planar structured PSCs with high PCEs. However, existence of chloride ions in the final perovskite film is still under debate. Contrastingly, few studies reported a negligible amount or absence of chloride ions in the final film, while others reported detection of chloride ions in the final film. Herein, we observed the microstructure and chlorine content of MAPbI3−xClx thin films with increasing temperature via an in-situ nano-Auger spectroscopy and in-situ scanning electron microscopic analysis. The relative precipitation of MAPbI3−xClx films occur at lower temperature and MAPbI3−xClx grains grow faster than those of MAPbI3 grains. Local concentrations of chlorine at intragrain and the vicinity of grain boundary were analyzed to understand the behavior and role of the chloride ions during the microstructural evolution of the MAPbI3−xClx films.

Chlorine distribution management for spectrally stable and efficient perovskite blue light-emitting diodes

Abstract Blue emitting perovskite electroluminescent (EL) devices are mainly realized based on chlorine mixing in bromide perovskites including CsPbBr3, CH3NH3PbBr3 (MAPbBr3), and CH(NH2)2PbBr3 (FAPbBr3). However, the inhomogeneous distribution and varied mobility of Cl− and Br− ions in alloyed perovskite films always result in EL spectra gradually shifting from blue to green region during device operation. Herein, alloyed FAPbBr3−xClx nanocrystal (NC) films with optimized Cl distribution are fabricated through employment of Cl terminated amine ligands (Cl-ligands). The as fabricated FAPbBr3−xClx NC films exhibit a Cl rich surface and 9 nm blue shifted emission spectrum compared to FAPbBr3−xClx films fabricated by conventional Br terminated ligands (Br-ligands). Furthermore, EL devices based on Cl-ligands achieve blue EL emissions with maximum luminance of 2810 cd/m2 and EQE of 3.1%, which is almost three times higher than that of EL devices based on Br-ligands. Importantly, Cl-ligands derived EL devices show greatly enhanced spectra stability with only slightly red-shifted EL spectra during device operation in a wide bias range, providing an alternative strategy for spectrally stable perovskite blue light-emitting diodes.

Determination of the complete set of optical parameters of micron-sized polycrystalline CH3NH3PbI3−xClx films from the oscillating transmittance and reflectance spectra

The complete set of optical parameters of micron-sized polycrystalline CH3NH3PbI3−xClx films deposited by the vacuum co-evaporation of lead iodide and methylammonium chloride is determined by analysis of oscillating optical transmittance and reflectance spectra in the wavelength range 400–1000 nm. It is shown that for a medium and weak absorption region the envelope method is valid for the extraction of refractive index, extinction and absorption coefficient when is using only transmittance spectra. As well thickness of the film is determined from transmittance and reflectance spectra with interference-effect. The absorption coefficient for the strong absorption region and optical band gap (direct transition at Eopt = 1.62 eV) are calculated based on transmittance and reflectance spectra by using conventional approximated formulas.

Well-grown low-defect MAPbI3–xClx films for perovskite solar cells with over 20% efficiency fabricated under controlled ambient humidity conditions

The conventional [(CH3NH3I (MAI)):PbI2:PbCl2 = 3 : 0: 1 [abbreviated as (3:0:1)]] precursor solution is known to result in CH3NH3PbI3–xClx films with large grain sizes when processed in an inert atmosphere, but it gives non-uniform perovskite films containing lots of voids and cracks when processed in ambient air. Furthermore, a dramatically longer annealing time (usually 100 min) is required for these films (3:0:1) due to the slow formation of the MAPbI3 phase via MACl loss, which is not conducive to perovskite film formation under ambient conditions due to perovskite degradation upon long exposure to moisture. Pure MAPbI3 films can be formed very rapidly from (1:1:0) (MAI:PbI2:PbCl2 = 1 : 1: 0) solution within a short annealing time, but they show small grain sizes and poor film quality. This work demonstrated that a fractional substitution of PbI2 with PbCl2 in the ([MAI]:[PbI2] = 1 : 1) precursor solution has a significant influence on film morphology and quality in terms of crystallization rate, grain size, crystallinity, and trap density of the formed perovskite film. Perovskite films can be formed with 5-min annealing at 100 °C from the precursor (MAI: PbI2:PbCl2 = 1: 0.8 : 0.2) processed in ambient air (humidity, 20% RH), exhibiting more uniform, increased grain size and higher film quality with reduced trap densities compared to film (1:1:0), thus leading to significantly improved power conversion efficiency (PCE), from 16.7% for perovskite solar cells (PrSCs) based on film (1:1:0) to 20.04% for the cell based on film (1:0.8:0.2). Further, the effects of R (R = [MAI]/[PbI2+PbCl2]) on morphology, hole mobility, carrier lifetime and efficiency of PrSCs were systematically and thoroughly investigated. This study found that MAPbI3–xClx at R = 1 can enable the highest hole mobility and longest carrier lifetime, thus giving the best performance at R = 1.

Acetylacetone Improves the Performance of Mixed Halide Perovskite Solar Cells

In this contribution, we show CH3NH3PbI3–xClx perovskite solar cells (PSCs) processed in ambient air from a solution containing the diketone, acetylacetone (AA) solvent as an additive. PSCs with the AA additive show enhanced photovoltaic properties. The optimized PSC with 10 vol % AA additive shows an average open-circuit voltage (VOC) of about 1.02 V, short-circuit current density (Jsc) of around 18.7 mA/cm2, fill factor of about 76%, and power conversion efficiency of around 14.5%. Atomic force microscopy topographic imaging depicts that the addition of AA into the MAPbI3–xClx solution enhances the crystal growth with comparable improvement in the surface smoothness. Electrochemical impedance spectroscopy and intensity modulated photovoltage spectroscopy investigations show that incorporation of AA resulted in the improvement of charge carrier dynamics in the bulk and across interfaces, and reduction of recombination pathways. Moreover, MAPbI3–xClx films with the AA additive exhibit stronger photoluminescence compared to the pristine MAPbI3–xClx films. This appears to confirm that the AA solvent additive plays a vital role to reduce the trap states and recombination conduits across the film, which boosts the enhancement of radiative recombination pathways. We believe that this additive is highly practical and a viable option to fabricate and optimize large-area, stable, thin film PSCs in ambient environment.

Impact of solvent exposure on the structure and electronic properties of CH3NH3PbI3−xClx mixed halide perovskite films

Organic semiconductor charge transport layers are important constituents of perovskite-based solar cells. To assess the suitability of potential solvents for the deposition of the charge transport layers on perovskite surfaces, the effect of solvent exposure on the properties of methyl ammonium lead mixed halide CH3NH3PbI3–xClx films is investigated by grazing incidence X-ray diffraction, atomic force microscopy, ultraviolet–visible absorption spectroscopy, and photoelectron spectroscopy. While exposure to dimethylformamide (DMF) and water instantly dissolves the perovskite film, exposure to chlorobenzene (CB) and chloroform (CF) does not detectably affect the perovskite bulk properties. However, the electronic properties of the perovskite surface are substantially modified by the solvent exposure, resulting in an increased work function and less n-type appearance.

Flexible, UV-responsive perovskite photodetectors with low driving voltage

Although lead halide perovskites with tunable band gaps are widely used for photodetection in the visible spectrum, very few studies have been focused on the use of perovskites in ultraviolet detection. Here, we report that MAPbI3−xClx-based photodetectors (PDs) show a response in the ultraviolet spectrum as well as yield very fast photoresponse speed (< 80 µs/90 µs) and excellent detectivity (1012 Jones with 365 nm lamp) with very low driving voltage (0.3 V). The results demonstrate the enhancement of photoelectric performance of the PDs in the ultraviolet spectrum is because the doping of Cl in MAPbI3 increases the bandgap and the crystalline grain size of MAPbI3−xClx film. Moreover, 10%PbCl2-MAPbI3−xClx-based flexible photodetectors displays remarkable mechanical flexibility.

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.

The stable perovskite solar cell prepared by rapidly annealing perovskite film with water additive in ambient air

In this work, an efficient and stable inverted planar perovskite solar cell (PSC) with water additive has been prepared in ambient air. Adding moderate water additive to CH3NH3PbI3−xClx precursor solution leads to growth in quality of CH3NH3PbI3−xClx film, because the boiling point of water is lower than that of N, N-dimethylformamide. The annealing temperature of the CH3NH3PbI3−xClx film is controlled to 105°C (slightly higher than the boiling point of water) to obtain the dense perovskite film rapidly in ambient environment with ~ 40% relative humidity. The highest power conversion efficiency (PCE) of PSC with water additive is 14.02%, higher than that (11.17%) of the reference device without water additive. In addition, the aqueous CH3NH3PbI3−xClx solution is transformed into the stable perovskite film through the method of rapid annealing. The stable CH3NH3PbI3−xClx·nH2O system can resist the decomposition of perovskite film and weaken iodide ion migration in PSCs, which enhance stability of the device under the atmospheric environment. After being stored in the air for 120h, the PSC device with water additive still has an PCE of 12.01%, higher than that (1.64%) of the reference device.

PEDOT:PSS-CrO3 composite hole-transporting layer for high-performance p-i-n structure perovskite solar cells

A solution-processed hole-transporting layer for planar perovskite solar cells (PSCs) is developed by simply incorporating the CrO3 aqueous solution into the ploy(3,4-ethylene-dioxythiophene):ploystyrenesulfonate (PEDOT:PSS) aqueous dispersion. Besides the merits of high conductivity and interface modification, PEDOT:PSS-CrO3 composite films can act as a good underlayer for the growth of the crystal perovskite films. The CH3NH3PbI3−xClx film deposited on the PEDOT:PSS-CrO3 underlayer demonstrates high quality with large-scale domains and good film uniformity, which results in obvious improvement of the absorption in almost whole visible-light range. The resulting PSC device shows a power conversion efficiency (PCE) as high as 16.90%.

Flexible Perovskite Solar Cells onto Plastic Substrate Exceeding 13% Efficiency Owing to the Optimization of CH3NH3PbI3–xClx Film via H2O Additive

In this work, flexible perovskite solar cells (F-PSCs) are fabricated utilizing the device polyethylene terephthalate (PET) substrate/ITO/PEDOT:PSS/CH3NH3PbI3–xClx/PCBM/Ag, which exhibits the optimal power conversion efficiency (PCE) reaching 13.27%, superb stability against bending deformation, and advantageous stability in ambient atmosphere without encapsulation. Meanwhile, we herein confirm a fact that incorporating suitable H2O additive into the perovskite precursor solution leads to an enhanced CH3NH3PbI3–xClx perovskite quality for F-PSCs application, including the improvement of morphology and electrical properties. To better summarize the mechanism concerning how H2O additive affects the perovskite film quality, CH3NH3PbI3–xClx films are prepared by a simple one-step spinning method from a solution containing CH3NH3I, PbI2, and PbCl2 in a mixed solvent of H2O and dimethylformamide (DMF) with solely various volume ratio ranging from 0.1% to 0.9%. Through a comparative analysis, it is proposed that H2O additive prolongs the CH3NH3PbI3–xClx recrystallization process contributing to slower crystallization rate. Additionally, it can merge adjacent perovskite grain together by accelerating the diffusion of ions within the predeposited films toward the grain boundary, thereby yielding large and densely packed perovskite grain size.

Improved perovskite film quality and solar cell performances using dual single solution coating

In this study, we present high quality perovskite CH3NH3PbI3−xClx thin films prepared by a combination of static and dynamic coating approaches, named dual single solution coating. Static coating, dynamic coating and the combination of these are comparatively studied. Scanning electron microscopy, X-ray diffraction, atomic force microscopy, UV-visible spectroscopy, and photoluminescence techniques are used for the determination of morphological, structural, and optical properties of thin films prepared using different coating approaches and deposition temperatures. All the coating approaches are repeated at room temperature and with hot deposition. The high quality and density CH3NH3PbI3−xClx films with full surface coverage are obtained using the dual single solution coating, particularly with hot-deposition. The perovskite solar cells prepared by the dual coating approach with hot deposition have better values for all the performance parameters in comparison to the other coating approaches, resulting in high efficiencies. The best device has a short circuit current of 22.03 mA/cm2, an open circuit voltage of 0.91 V, a fill factor of 0.73, and a power conversion efficiency of 14.68% from short-circuit to forward bias, and 22.39 mA/cm2, 0.91 V, 75% and 15.32% for the vice-versa, respectively.

Effects of copper addition on photovoltaic properties of perovskite CH3NH3PbI3−xClxsolar cells

This paper presents the effects of copper (Cu) addition on the photovoltaic properties of perovskite CH3NH3PbI3−xClx solar cells. The effects were investigated by measuring the current density–voltage (J–V) characteristics and external quantum efficiency. In the present work, CuBr and CuBr2 were used as additives. The photovoltaic properties of the CuBr‐added CH3NH3PbI3−xClx devices showed a clear improvement. Structural and optical properties of the CuBr‐ and CuBr2‐added CH3NH3PbI3−xClx films were also investigated. Based on the present results, the changes in the photovoltaic properties were discussed.

Growth of freestanding lead dual-halide thin film and microbulk via hydrothermal method

In this paper, we report a facile growth of freestanding PbI2−xClx film and microbulk via hydrothermal method without additives. The properties of samples were systematically investigated by field emission scanning electron microscopy, x-ray diffraction and UV–vis diffuse reflection spectroscopy. The results reveal that there appears to be two types of morphological PbI2−xClx due to the anisotropy in the effective surface energy, and the underlying growth mechanism behind the observation is also discussed. This new approach is promising for the fabrication of PbI2−xClx precursor material of detectors and solar cells.

Stabilizing Hybrid Perovskites Via Non-Hydrolytic Atomic Layer Deposited Overlayers

A significant challenge to the practical application of hybrid perovskites remains for photovoltaic application. Specifically, the presence of hygroscopic ionic small molecules – alkylammonium cations – has been identified as a primary source of the absorber's sensitivity towards any moisture and any temperatures greater than 150 °C. CH3NH3PbI3 , for instance, rapidly degrades upon exposure to modest relative humidity even at room temperature via: CH3NH3PbI3(s) → PbI2(s) + CH3NH3I(aq) A related, but distinct, decomposition pathway is induced by heating above 150 °C even under an inert and dry environment, where methylamine and hydroiodic acid have measurable vapor pressure: CH3NH3PbI3(s) → PbI2(s) + CH3NH2↑ + HI↑ Various attempts have been made to improve system stability including modification of chemistry, two dimensional (2D) hybrid perovskites, and macroscopic encapsulation. While these measures may slow degradation the effect is often modest, transient, and adds significant device complexity. Synthetically-compatible, pinhole-free functional overlayers, in contrast, would provide a simple route to surface chemical passivation as well as a physical barrier to diffusion in or out of the active layer. Atomic Layer Deposition (ALD) is a vapor-phase deposition technique with the capability to produce ultra-thin and pinhole-free films with well-defined surface chemical control and precise physical thickness, providing a good match to these challenges. However, the vast majority of oxide ALD processes invoke water (H2O), hydrogen peroxide (H2O2) or ozone (O3) as oxygen sources, often at temperatures greater than 150 °C. Unfortunately, these chemicals and temperatures are predicted to be in direct conflict with most hybrid perovskite halides and therefore may preclude an integrated overlayer approach. However, we report low temperature non-hydrolytic (i.e. waterless) ALD to establish stabilizing overlayers of Al2O3 or TiO2 directly on CH3NH3PbI3−xClx films. We demonstrate not only that oxide ALD conditions exist that are compatible with hybrid perovskite halides, but that the resulting systems exhibit dramatically improved stability against moisture (85% RH) and enhanced resistance to considerably higher temperatures (up to 250 °C) and even liquid water. We further demonstrate the capability of nh-TiO2 to serve a dual role – stabilizing the absorber underlayer and accepting electrons in future inverted photovoltaics.The figure shows the effect of a liquid water drop after two minutes directly on a perovskite halide thin film, without and with an ultrathin hybrid ALD passivation layer. Figure 1

Improved performance of perovskite solar cell by controlling CH3NH3PbI3−xClx film morphology with CH3NH3Cl-assisted method

Sequential deposition solution-based method has been widely used for the fabrication of perovskite solar cells (PSCs). However, there is still a challenge to achieve homogeneous and consecutive surface of the perovskite layers. In this work, CH3NH3PbI3−xClx layers were prepared by a modified two-step solution method. Specifically, the optimum amount of CH3NH3Cl pre-added into PbI2 precursor solution, the appropriate size of pinholes and voids appear in PbI2 films and leave room for the growth of CH3NH3PbI3−xClx crystal. Under this condition, the crystal grains size is diminished and the surface coverage ratio of CH3NH3PbI3−xClx film is enhanced, which prevent the combination of electron-hole pairs on the interface between perovskite layer and TiO2 substrate. By varying the CH3NH3Cl amounts, the PSC devices displayed the highest power conversion efficiency of 13 %, which was obviously higher than that of the one prepared via transitional routes (10.32 %). As a result, we developed a simple and repeatable route for controllable synthesis of perovskite absorption layers, which is demonstrated to be effective to improve the performance of PSCs.