CH3NH3PbBr3 Films Research Articles

CH3NH3PbI3 and CH3NH3PbBr3 films deposited by automated spray-pyrolysis for applications in photovoltaic energy

CH3NH3PbI3 and CH3NH3PbBr3 films deposited by automated spray-pyrolysis for applications in photovoltaic energy

Reverse bias breakdown and photocurrent gain in CH3NH3PbBr3 films

Perovskite films are promising candidates for fast, sensitive, and large area photodetectors. A gain in perovskite based detectors has been observed in several architectures, but a model describing the underlying mechanism is still missing or at least incomplete. Here, we present measurements of CH3NH3PbBr3 films under reverse bias exhibiting breakdown at 4–5 V and small photocurrent gain ≲ 2, which based on a phenomenological model, we explain tentatively by tunnel-assisted injection from the TiO2 electron transport layer and carrier multiplication, mediated by the electric field due to mobile ions.

Highly Luminescent and Patternable Block Copolymer Templated 3D Perovskite Films

AbstractThe rapid development of lead halide perovskite light emitting diodes (PeLED) provides bright prospects for future lighting and display applications. However, the lack of efficient blue light emission, the insufficient device stability, and the shortage of convenient patterning methods greatly impede the development of PeLED applications. In this work, a feasible two‐step fabrication method combined with a block copolymer (BCP) template is introduced to fabricate high quality CH3NH3PbBrxCl3−x 3D perovskite film. The BCP‐templated CH3NH3PbBr3 film possesses a state‐of‐the‐art photoluminescence quantum yield (PLQY) of 62% in the champion sample (58% average PLQY) and an outstanding stability at room temperature. Using halide‐free lead acetate trihydrate as the lead source, the color of the photoluminescence can be tuned easily from green to blue by simply controlling the Cl/Br ratio in the second step. A sky‐blue emission is obtained from a CH3NH3PbBr1.5Cl1.5 perovskite film with a PLQY of 23 ± 2%. The two‐step fabrication approach can also enable straightforward patterning, as demonstrated with inkjet printing and Chinese calligraphy.

Study of compositional stability and related optical properties of perovskite CH3NH3PbBr3 films fabricated via two-step sol-gel process using weakly coordinating isopropanol solvent

Compositional stability of perovskites is crucial for perovskite solar cells (PSCs) application because of directly affecting the performance of PSCs. Highly crystallized perovskite MAPbBr3 (MA = CH3NH3) with micronscale crystallites are usually fabricated via the one-step sol-gel process that uses strongly coordinating organic solvents. The two-step sol-gel process using weakly coordinating organic solvent is rarely used to fabricate MAPbBr3 films with relatively small crystallites. However, the two-step sol-gel process is preferred to fabricate PSCs because the residual PbBr2 can prevent the direct contact between electron- and hole-transporting layers. Thus in this work, perovskite MAPbBr3 films are fabricated via two-step sol-gel process using weakly coordinating isopropanol solvent. The compositional stability in dry ambient air and related optical properties of the films are intensively studied by a technique of post-annealing. A compositional transition from MAPbBr3 to PbBr2 occurs with increase of post-annealing temperature (Tpa). The product PbBr2 begins to form in the MAPbBr3 films at approximately 130 °C Tpa, and MAPbBr3 is fully thermally degraded to PbBr2 at 170 °C Tpa. The compositional stability of the films in dry air is inherently determined by instable organic cations (MA)+ and small electronegativity of Br−. The perovskite film initially shows a redshifted and then a blueshifted optical absorption edge with increase of Tpa, which is due to the decrease in film tensile stress and to the enhancement in thermal degradation to PbBr2, respectively. The increase in number of PbBr2 particles and defects in the films remarkably reduces the intensity of the green emission of MAPbBr3.

Composition engineering to obtain efficient hybrid perovskite light-emitting diodes.

Metal halide perovskites have received considerable attention in the field of electroluminescence, and the external quantum efficiency of perovskite light-emitting diodes has exceeded 20%. CH3NH3PbBr3 has been intensely investigated as an emitting layer in perovskite light-emitting diodes. However, perovskite films comprising CH3NH3PbBr3 often exhibit low surface coverage and poor crystallinity, leading to high current leakage, severe nonradiative recombination, and limited device performance. Herein, we demonstrate a rationale for composition engineering to obtain high-quality perovskite films. We first reduce pinholes by adding excess CH3NH3Br to the actual CH3NH3PbBr3 films, and we then add CsBr to improve the crystalline quality and to passivate nonradiative defects. As a result, the (CH3NH3)1-xCsxPbBr3 based perovskite light-emitting diodes exhibit significantly improved external quantum and power efficiencies of 6.97% and 25.18 lm/W, respectively, representing an improvement in performance dozens of times greater than that of pristine CH3NH3PbBr3-based perovskite light-emitting diodes. Our study demonstrates that composition engineering is an effective strategy for enhancing the device performance of perovskite light-emitting diodes.

Widegap CH3NH3PbBr3 solar cells for optical wireless power transmission application

The optoelectrical properties of bromide-based perovskite thin films were evaluated to develop an optical wireless power transmission system. CH3NH3PbBr3 (MAPbBr3) films were deposited by the anti-solvent method after substrate preheating. The low-temperature exciton emission and discontinuous peak shift from phase transitions in the emission spectra indicate the high optical quality of MAPbBr3 films on TiO2. The Urbach energy and diffusion length of the MAPbBr3 thin films on TiO2 were 22.7 meV and 1.14 μm, respectively. The films exhibited good solar cell performance under monochromatic light with an efficiency over 20%.

Robust and Transient Write‐Once‐Read‐Many‐Times Memory Device Based on Hybrid Perovskite Film with Novel Room Temperature Molten Salt Solvent

AbstractOrganic–inorganic hybrid perovskites (OIHPs) have emerged as a novel class of functional materials with applications in solar cells, photodetectors, light‐emitting diodes, and resistive switching memories. Generally, perovskite films are fabricated with toxic solvents and antisolvent technique under inert atmosphere, which limits the commercial applications of OIHP‐based devices. To address this issue, uniform CH3NH3PbBr3 (MAPbBr3) film is fabricated through a facile one‐step spin‐coating method by directly dissolving perovskite precursor in a room‐temperature molten salt methylammonium acetate under air ambient condition. The nonvolatile resistive switching devices based on MAPbBr3 exhibit robust and reproducible write‐once‐read‐many‐times (WORM) memory properties with a large ON/OFF ratio (106), reliable retention properties (104 s), and somewhat ternary resistive characteristic. The conductive filaments in the perovskite thin film are proposed to induce the electrical conductivity switching. Additionally, the MAPbBr3 films can be dissolved rapidly in deionized water within 5 s, showing the transient characteristics. This work demonstrates a new perspective on the perovskite film fabrication and shows the potential application of MAPbBr3 in transient WORM devices.

High-Quality MAPbBr3 Cuboid Film with Promising Optoelectronic Properties Prepared by a Hot Methylamine Precursor Approach.

Though CH3NH3PbBr3 single crystals are frequently applied in various optoelectronic devices due to their favorable cuboid geometry, superior optoelectronic properties, and better stability than CH3NH3PbI3, CH3NH3PbBr3 polycrystalline films normally show poorer morphology with scattered crystals than their iodide counterparts, inherently due to their different crystallization habits. In this work, a facile process based on a hot methylamine-based precursor with high viscosity and concentration is demonstrated to counteract rapid ion diffusion. The precursor also has special features including a large colloidal size, a solid form at room temperature, and fast crystallization offered by the easy evacuation of methylamine. CH3NH3PbBr3 films composed of tightly aligned CH3NH3PbBr3 cuboids on micron scale are obtained. Wide channel (100 μm) photodetectors made from the CH3NH3PbBr3 films show promising photoresponse and fast response speeds on par with those based on single crystals, suggesting high film quality and good optoelectronic connections between neighboring cuboids.

Stable fluorescent NH3 sensor based on MAPbBr3 encapsulated by tetrabutylammonium cations

Recently, organic-inorganic halide perovskite materials were investigated on gas sensing due to their excellent optical properties and gas sensitivities. Here, we designed a stable fluorescent perovskite-based sensor for NH3 detection, in which the CH3NH3PbBr3 (MAPbBr3) film was deposited on the GeO2 substrate and also capped by tetrabutylammonium (TBA) ligand as a stabilizing agent. This as-fabricated MAPbBr3-TBA-based sensor exhibited the relatively strong and stable photoluminescence (PL) intensity, thereby expanding the fluorescence response range for NH3 sensing. Upon exposure to NH3 gas, the PL intensity quenched rapidly by 62.5% with short response time (61 s) and recovery time (65 s). The sensor also possessed a linear relationship between the PL intensity and concentration of NH3 in the range of 0–100 ppm, and presented excellent reversibility, high gas selectivity, and humidity stability. Furthermore, the NH3 sensing mechanism was investigated based on X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Differential thermal analysis-Thermogravimetry (DTA-TG) and fluorescence lifetime measurements, in which the NH3 molecules might permeate the capped TBA ligand and then induce structure transformation of inner MAPbBr3 crystal. This study indicated that the as-prepared MAPbBr3-TBA-based sensor might provide promising applications on NH3 gas detection.

Atmosphere dependent gas-solid reaction for high-quality MAPbBr3 perovskite solar cells

Abstract It is imperative to develop a high-quality hybrid perovskite film with large crystallinity and smooth morphology for high-performance stable perovskite solar cells. Herein, vapor assisted crystallization method was used to fabricate crystalline CH3NH3PbBr3 (MAPbBr3) films through the precisely controlled gas-solid reaction. The effect of different atmosphere condition (N2, vacuum and air conditions) on the final MAPbBr3 films was investigated. It is found that the N2 atmosphere is in favor for obtaining uniform perovskite film (MAPbBr3-N2) which exhibits good crystallization, strong absorption and few defects due to the slow crystallization reaction. In this way, the MAPbBr3-N2-based device shows an open-circuit voltage (Voc) of 1.20 V and power conversion efficiency (PCE) of 4.88%, much higher than the devices fabricated in the vacuum state. Based on this atmosphere, a champion PCE of 7.30% with a Voc of 1.384 V can be achieved by introducing mesoporous TiO2 layer. Our results could provide valuable information for the fabrication of high-quality perovskite films for photoelectric device.

Enhanced emission from CH3NH3PbBr3 perovskite films by graphene quantum dot modification

Organic-inorganic hybrid perovskites have emerged as promising emitters with the benefits of low cost and high color purity, but their low luminescence efficiency is a drawback for practical application on light emitting devices. Here we show that by incorporating proper amount of graphene quantum dots (GQDs) into perovskite precursor, dense CH3NH3PbBr3 films with reduced grain size and well passivated grain boundaries could be obtained. This gives rise to enhanced emission from GQD modified perovskite films. Our work thus provides a viable way to prepare highly luminescent perovskite films for optoelectronic applications.

Surface-enhanced spin current to charge current conversion efficiency in CH3NH3PbBr3-based devices.

Hybrid organic-inorganic perovskites have shown great promise for spintronic applications due to their large spin-orbit coupling induced by the Pb and halogen atoms. Particularly, the large observed surface-induced Rashba splitting in CH3NH3PbBr3 indicates efficient spin-current-to-charge-current (StC) conversion, which, however, has not been demonstrated yet. In this work, the StC conversion efficiency in ferromagnet/CH3NH3PbBr3-based devices is studied using the pulsed spin-pumping technique measured by the inverse spin Hall effect. We found that the StC conversion efficiency is anomalous in that it increases at small perovskite layer thickness. This indicates the existence of a surface-dominated StC mechanism such as the inverse Rashba-Edelstein effect. By inserting a thin LiF layer between the ferromagnet and the perovskite film, the StC conversion efficiency is greatly suppressed, validating the existence of a Rashba surface in the CH3NH3PbBr3 film.

Addition of Monovalent Silver Cations to CH3NH3PbBr3 Produces Crystallographically Oriented Perovskite Thin Films

The incorporation of monovalent silver (Ag+) cations into methylammonium lead bromide (CH3NH3PbBr3) perovskite films leads to a strongly preferred (001) crystallographic orientation on a wide variety of substrates, ranging from glass to mesoporous TiO2. CH3NH3PbBr3 films deposited without Ag+ exhibit only a weakly preferred (011) orientation. Compositional maps and depth profiles from time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveal Ag+ segregated to grain boundaries and interfaces. In photovoltaic devices (PVs), addition of Ag+ to MAPBr films resulted in poorer device performance, most likely because of the observed Ag+ segregation in the films.

Improved Efficiency of Perovskite Light-Emitting Diodes Using a Three-Step Spin-Coated CH3NH3PbBr3 Emitter and a PEDOT:PSS/MoO3-Ammonia Composite Hole Transport Layer

High efficiency perovskite light-emitting diodes (PeLEDs) using PEDOT:PSS/MoO3-ammonia composite hole transport layers (HTLs) with different MoO3-ammonia ratios were prepared and characterized. For PeLEDs with one-step spin-coated CH3NH3PbBr3 emitter, an optimal MoO3-ammonia volume ratio (0.02) in PEDOT:PSS/MoO3-ammonia composite HTL presented a maximum luminance of 1082 cd/m2 and maximum current efficiency of 0.7 cd/A, which are 82% and 94% higher than those of the control device using pure PEDOT:PSS HTL respectively. It can be explained by that the optimized amount of MoO3-ammonia in the composite HTLs cannot only facilitate hole injection into CH3NH3PbBr3 through reducing the contact barrier, but also suppress the exciton quenching at the HTL/CH3NH3PbBr3 interface. Three-step spin coating method was further used to obtain uniform and dense CH3NH3PbBr3 films, which lead to a maximum luminance of 5044 cd/m2 and maximum current efficiency of 3.12 cd/A, showing enhancement of 750% and 767% compared with the control device respectively. The significantly improved efficiency of PeLEDs using three-step spin-coated CH3NH3PbBr3 film and an optimum PEDOT:PSS/MoO3-ammonia composite HTL can be explained by the enhanced carrier recombination through better hole injection and film morphology optimization, as well as the reduced exciton quenching at HTL/CH3NH3PbBr3 interface. These results present a promising strategy for the device engineering of high efficiency PeLEDs.

Anti-solvent engineering for efficient semitransparent CH3NH3PbBr3 perovskite solar cells for greenhouse applications

Abstract With ideal combination of benefits that selectively converts high photon energy spectrum into electricity while transmitting low energy photons for photosynthesis, the CH3NH3PbBr3 perovskite solar cell (BPSC) is a promising candidate for efficient greenhouse based building integrated photovoltaic (BIPV) applications. However, the efficiency of BPSCs is still much lower than their theoretical efficiency. In general, interface band alignment is regarded as the vital factor of the BPSCs whereas only few reports on enhancing perovskite film quality. In this work, highly efficient BPSCs were fabricated by improving the crystallization process of CH3NH3PbBr3 with the assistance of anti-solvents. A new anti-solvent of diphenyl ether (DPE) was developed for its strong interaction with the solvents in the perovskite precursor solution. By using the anti-solvent of DPE, trap-state density of the CH3NH3PbBr3 film is reduced and the electron lifetime is enhanced along with the large-grain crystals compared with the samples from conventional anti-solvent of chlorobenzene. Upon preliminary optimization, the efficiencies of typical and semitransparent BPSCs are improved to as high as 9.54% and 7.51%, respectively. Optical absorption measurement demonstrates that the cell without metal electrode shows 80% transparency in the wavelength range of 550–1000 nm that is perfect for greenhouse vegetation. Considering that the cell absorbs light in the blue spectrum before 550 nm, it offers very high solar cell efficiency with only 17.8% of total photons, while over 60% of total photons can transmit through for photosynthesis if a transparent electrode can be obtained such as indium doped SnO2.

Spin-Coated CH₃NH₃PbBr₃ Film Consisting of Micron-Scale Single Crystals Assisted with a Benzophenone Crystallizing Agent and Its Application in Perovskite Light-Emitting Diodes.

Owing to the superior properties of optical and electronic properties, perovskite single crystals have been in high demand recently. However, the growth of large-sized single crystals requires several processing steps and a long growth time, which engenders great difficulties in device integration. Herein, benzophenone (BP) was firstly introduced as a crystallizing agent to facilitate the construction of a high-quality CH3NH3PbBr3 (MAPbBr3) film consisting of micron-scale single crystals in a one-step spin-coating method. We studied the influence of the BP concentration upon the size and shape of the micron-scale single crystals. Moreover, due to the enhanced morphology of the MAPbBr3 film with low-defect micron-scale single crystals, perovskite light-emitting diodes (PeLEDs) have been demonstrated with a maximum luminance of 1057.6 cd/m2 and a turn-on voltage as low as 2.25 V. This approach not only proposes a concise and highly repeatable method for the formation of micron-scale perovskite single crystals, but also paves a way for the realization of efficient PeLEDs.

Bulk Heterojunction-Assisted Grain Growth for Controllable and Highly Crystalline Perovskite Films.

Perovskite optoelectronic devices are being regarded as future candidates for next-generation optoelectronic devices. Device performance has been shown to be influenced by the perovskite film, which is determined by the grain size, surface roughness, and film coverage; therefore, developing controllable and highly crystalline perovskite films is pivotal for highly efficient devices. In this work, an innovative bulk heterojunction (BHJ)-assisted grain growth (BAGG) technique was developed to accurately control the quality of perovskite films. By a simple modulation of the polymer-to-PC61BM ratio in the BHJ film, the transition to a complete film phase from the perovskite precursor was accurately regulated, resulting in a controllable perovskite grain growth and high-quality final perovskite film. Moreover, because the BHJ layer could seep deeply into the perovskite active layer through the grain boundaries in the BAGG process, it facilitated the interface engineering and charge transport. The perovskite solar cells containing an optimized CH3NH3PbI3 film presented a high efficiency of 18.38% and fill factor of 83.71%. The perovskite light-emitting diode that contained a nanoscale and uniform CH3NH3PbBr3 film with full coverage presented enhanced emission properties with a brightness value of 1600 cd/m2 at 6.0 V and a luminous efficiency of 0.56 cd/A.

Strong nonlinear absorption in perovskite films

In this work, we report a comparative study of the nonlinear optical responses of CH3NH3PbX3 (where X is a chlorine, bromine, or iodine halogen atom) perovskite thin (~200 nm) films using 40 fs, 800 nm pulses. We found that these films possess strong nonlinear absorption coefficients comparable with the highest reported values for thin film structures (up to 7 × 10−7 cm W−1). We also analyze the photoluminescence emission from CH3NH3PbBr3 film and demonstrate the quadratic dependence of emission intensity on the intensity of probe pulse indicating a two-photon mechanism of luminescence.

Emissive edge state in CH3NH3PbBr3 films probed by fluorescence lifetime imaging technique

Organometallic hybrid perovskites have attracted intense attentions recently, as a new family of solution processable semiconductors for photoenergy conversion and light emission purposes. Specifically, CH3NH3PbBr3 is one type of emissive perovskites, but its quantum efficiency largely depends on the preparation procedure. Here, we use the fluorescence lifetime imaging (FLIM) technique to investigate the relation between microscopic structures and photoluminescence (PL) in CH3NH3PbBr3 polycrystalline films. By dripping poor solvents (chlorobenzene or chloroform) to accelerate the crystallization during the film preparation, we could decrease the crystal domain size from 10 μm down to 500 nm, and the corresponding PL intensity increases significantly. From the FLIM characterization of these films, we find that the PL emission is mostly from the edge of crystal domains. The PL dynamics indicates that the radiative decay of edge state is much more efficient than that of the bulk state, and the bulk state of photoexcitation undergoes an energy transfer to the edge state. This finding explains the origin of enhanced PL from CH3NH3PbBr3 films when treated with poor solvents and provides useful information for further improvement on the PL efficiency of hybrid perovskite materials.

Grain Size Modulation and Interfacial Engineering of CH3 NH3 PbBr3 Emitter Films through Incorporation of Tetraethylammonium Bromide.

Metal halide perovskites have demonstrated breakthrough performances as absorber and emitter materials for photovoltaic and display applications respectively. However, despite the low manufacturing cost associated with solution-based processing, the propensity for defect formation with this technique has led to an increasing need for defect passivation. Here, we present an inexpensive and facile method to remedy surface defects through a postdeposition treatment process using branched alkylammonium cation species. The simultaneous realignment of interfacial energy levels upon incorporation of tetraethylammonium bromide onto the surface of CH3 NH3 PbBr3 films contributes favorably toward the enhancement in overall light-emitting diode characteristics, achieving maximum luminance, current efficiency, and external quantum efficiency values of 11 000 cd m-2 , 0.68 cd A-1 , and 0.16 %, respectively.