CH3NH3PbI3 Layer Research Articles

Morphology and surface analyses for CH3NH3PbI3 perovskite thin films treated with versatile solvent-antisolvent vapors.

Organometal halide perovskite (CH3NH3PbI3) semiconductors have been promising candidates as a photoactive layer for photovoltaics. Especially for high performance devices, the crystal structure and morphology of this perovskite layer should be optimized. In this experiment, by employing solvent–antisolvent vapor techniques during a modified sequential deposition of PbI2–CH3NH3I layers, the morphology engineering was carried out as a function of antisolvent species such as: chloroform, chlorobenzene, dichlorobenzene, toluene, and diethyl ether. Then, the optical, morphological, structural, and surface properties were characterized. When dimethyl sulfoxide (DMSO, solvent) and diethyl ether (antisolvent) vapors were employed, the CH3NH3PbI3 layer exhibited relatively desirable crystal structures and morphologies, resulting in an optical bandgap (Eg) of 1.61 eV, crystallite size (t) of 89.5 nm, and high photoluminescence (PL) intensity. Finally, the stability of perovskite films toward water was found to be dependent on the morphologies with defects such as grain boundaries, which was evaluated through contact angle measurement.

Optoelectronic and photo‐charging properties of CH3NH3PbI3/LiFePO4 system

SummaryThe photo‐responsive capability of lithium battery materials is a prerequisite to realize new‐generation light‐weight photo‐rechargeable batteries. However, the photo‐charging property is not available for common battery electrode materials such as LiFePO4. In this manuscript, we provide evidence that the halide perovskite material CH3NH3PbI3 is able to activate the photo‐charging properties of the lithium‐ion battery electrode material LiFePO4. The photoelectrochemical measurement demonstrates that the photo‐responsive property of the CH3NH3PbI3/LiFePO4 composite is significantly improved; the photo‐induced signals are neither observed in the individual halide perovskite nor the lithium battery material tested under the same condition. The first‐principles calculations reveal strong interactions between the CH3NH3PbI3 layer and the LiFePO4 layer via the coordination between the Lewis acid and Lewis base species; this forms a heterostructure that assists the photo‐charging process. We propose that the combination of halide perovskite materials and lithium battery electrode materials is a viable way to achieve light‐weight photo‐batteries. Suggestions to address the stability and voltage issues of the halide perovskite‐based hybrid systems toward the photo‐battery application are provided. This study facilitates the fundamental understanding of the integrated photo‐rechargeable battery materials and highlights the importance of halide perovskite materials for the lithium‐ion and photo‐rechargeable batteries.

Low-voltage room-temperature electrochemical deposition of perovskite films for solar cell devices

A uniform CH3NH3PbI3 layer was successfully deposited on a mesoporous TiO2 layer (mp-TiO2) via a two-step low-voltage room-temperature electrochemical deposition method without annealing. The deposited perovskite crystals were applied to cover a surface mp-TiO2 electron transport material and fill the nanoscale blank of mp-TiO2. A mesoporous electron transport material and a platinum sheet were used as working and counter electrodes, respectively. The obtained film was then utilized to fabricate a mesoporous hybrid perovskite solar cell (PSC) with the configuration of a fluorine-doped tin oxide/compact TiO2/mp-TiO2/perovskite/Spiro-OMeTAD/Au electrode. An efficiency of 15% was achieved by adjusting Pb and MAI deposition and by using champion cells with an active area of 2 mm × 2 mm at 1 sun under an AM 1.5 condition. The perovskite layers and PSCs were analyzed through several characterization methods. Results demonstrated that this deposition technology could be applied to easily control the morphological characteristics of perovskite layers. Thus, a high power conversion efficiency was obtained. This study proposed a possible perovskite deposition process and demonstrated that electrochemical deposition could have potential for application in PSC fabrication.

Interlayer Solid-Phase Reaction in Halide Perovskite Thin Films Fabricated Via Alternate Infrared Laser Deposition

It is now widely pursued to investigate the growth mechanism of halide perovskite thin films in detail to elucidate the degradation mechanism and to develop the thin films with superior photovoltaic properties. We have applied infrared laser molecular beam deposition (IRL-MBD), which can control the deposition of halide perovskite at the atomic layer level in ultra-high vacuum condition [1]. In our IRL-MBD process, CH3NH3PbI3 (MAPbI3) layers are formed by alternately depositing CH3NH3I (methylammonium iodide: MAI) and PbI2 layers, and subsequent interlayer solid-phase reaction at room temperature. In this study, we focus on the effect of the layer thickness on the interlayer solid-phase reaction and the properties of the formed MAPbI3 thin films.A synthetic silica substrate cleaned using organic solvents was introduced into the IRL-MBD chamber via a load lock. After that, PbI2 and MAI molecular beams were alternately irradiated onto the substrate by evaporating MAI and PbI2 sources using an infrared laser beam (wavelength: 808 nm, input power: 2~3 W). The deposition rate of PbI2 was controlled at 0.1 nm/s using a quartz crystal microbalance (QCM) thickness monitor and manual laser power control. The evaporation rate of MAI was manually adjusted so that the pressure in the chamber was kept at 4×10-4 Pa during the irradiation of MAI onto the substrate. Figure 1 shows a schematic layer structure of the samples A, B and C consisting of 1, 5 and 10 pair(s) of [MAI/PbI2] bilayer, respectively. The irradiation time of MAI and the nominal thickness of PbI2 were A: [80 min/300 nm]×1, B: [16 min/60 nm]×5 and C: [8 min/30 nm]×10.Figure 2 shows the X-ray diffraction (XRD) patterns obtained from the samples. The sample A shows two diffraction peaks corresponding to PbI2(001) and MAPbI3(110), while the samples B and C exhibits only single peak corresponding to MAPbI3(110) in the shown diffraction angle range. Figure 3 shows the schematic structure of the samples inferred from the results described above. In the sample A, PbI2 layer, which is not completely reacted with MAI, remains in the thin film. In contrast, in the samples B and C, only the phase of MAPbI3 is observed, indicating that PbI2 and MAI react completely by the interlayer solid-phase reaction. The results suggest that PbI2 has a critical film thickness that causes a complete interlayer solid-phase reaction with MAI at room temperature between 60 nm and 300 nm. The critical film thickness is likely comparable to the penetration depth of MAI into PbI2 and is supposed to be dependent on the temperature during the interlayer solid-phase reaction.[1] K. Kawashima, Y. Okamoto, O. Annayev, N. Toyokura, R. Takahashi, M. Lippmaa, K. Itaka, Y. Suzuki, N. Matsuki and H. Koinuma, Sci. and Tech. of Adv. Mater. 18, 307-315 (2017). Figure 1

Ambient Pressure X-ray Photoelectron Spectroscopy Investigation of Thermally Stable Halide Perovskite Solar Cells via Post-Treatment.

Long-term thermal stability is one limiting factor that impedes the commercialization of the perovskite solar cell. Inspired by our prior results from machine learning, we discover that coating a thin layer of 4,4'-dibromotriphenylamine (DBTPA) on top of a CH3NH3PbI3 layer can improve the stability of resultant solar cells. The passivated devices kept 96% of the original power conversion efficiency for 1000 h at 85 °C in a N2 atmosphere without encapsulation. Near-ambient pressure X-ray photoelectron spectroscopy (XPS) was employed to investigate the evolution of the composition and evaluate thermal and moisture stability by in situ studies. A comparison between pristine MAPbI3 films and DBTPA-treated films shows that the DBTPA treatment suppresses the escape of iodide and methylamine up to 150 °C under 5 mbar humidity. Furthermore, we have used attenuated total reflection Fourier transform infrared and XPS to probe the interactions between DBTPA and MAPbI3 surfaces. The results prove that DBTPA coordinates with the perovskite by Lewis acid-base and cation-π interaction. Compared with the 19.9% efficiency of the pristine sample, the champion efficiency of the passivated sample reaches 20.6%. Our results reveal DBTPA as a new post-treating molecule that leads not only to the improvement of the photovoltaic efficiency but also thermal and moisture stability.

High performance novel flexible perovskite solar cell based on a low-cost-processed ZnO:Co electron transport layer

In this work, high quality uniform and dense nanostructured cobalt-doped zinc oxide (ZnO:Co) films were used as electron-transport layers in CH3NH3PbI3-based planar heterojunction perovskite solar cells (PSCs) on a flexible conductive substrate. Highly photo catalytically active ZnO:Co films were prepared by a low cost hydrothermal process using the aqueous solution of zinc nitrate hexahydrate, hexamethylenete-tramine and cobalt (II) nitrate hexahydrate. ZnO:Co films were deposited on indium tin oxide (ITO) covered polyethylene terephthalate (PET) flexible substrates. The growth was controlled by maintaining the autoclave temperature at 150 °C for 4 h. The CH3NH3PbI3 layer was deposited on the ZnO:Co films by spin coating. Spiro-OMeTAD was employed as a hole-transporting material. The structural, morphology and optical properties of the grown ZnO nanostructures were characterized by X-ray diffraction (XRD), field-emission scanning electron microcopy (FESEM), energy-dispersive X-ray spectrometry (EDX), ultraviolet-visible (UV-Vis) and photoelectrochemical propriety. XRD spectra showed that both ZnO and ZnO:Co nanorods had a hexagonal wurtzite structure with a strong preferred orientation along the (002) plane. The surface morphology of films was studied by FESEM and showed that both the pure and Co-doped ZnO films had hexagonal shaped nanorods. In the steady state, the ZnO electrode gave a photocurrent density of about 1.5 mA/cm2. However, the Co-doped ZnO electrode showed a photocurrent density of about 6 mA/cm2, which is 4-fold higher than that of the ZnO electrode. Based on the above synthesized Co-doped ZnO films, the photovoltaic performance of PSCs was studied. The Co-doped ZnO layers had a significant impact on the photovoltaic conversion efficiency (PCE) of the PSCs. The latter was attributed to an efficient charge separation and transport due to the better coverage of perovskite on the nanostructured Co-doped ZnO films. As a result, the measured PCE under standard solar conditions (A M 1.5G, 100 mW/cm2) reached 7%. SCAPS-1D simulation was also performed to analyze the effect of the co-doped ZnO thin film on the corresponding solar cell performances.

Cu2O-HTM/SiO2-ETM assisted for synthesis engineering improving efficiency and stability with heterojunction planar perovskite thin-film solar cells

Perovskite solar cells (PSCs) have been made eligible for proficient power conversion efficiency (PCE) by optimizing the perovskite film’s morphology, formation, interfaces, and charge collection for increased effectiveness. This paper applied a new method for Cu2O/methylammonium lead iodide (MAPbI3)/SiO2 structure with heterojunction PSCs. This paper developed a novel synthesis engineering method for thin Cu2O hole-transporting material layer (HTML) and ultrathin SiO2 electron-transporting material layer (ETML). Cu2O HTML and SiO2 ETML could improve the PCE and carrier charge for recombination and recollection. The architecture includes a reduced film thickness by hetero-contact synthesis engineering, which resulted in an impactful enhancement of open-circuit voltage (Voc). The stable Voc effect was induced by constructing the interfilm of Cu2O and SiO2 between the main CH3NH3PbI3 layers, which transported electrons/electron holes, resulting in an excellent PCE of 18.4%. The fabrication showed that inorganic materials can be applied for the potential interfacial engineering of perovskite-based solar cells.

Annealing temperature effects on the performance of the perovskite solar cells

In this work, perovskite solar cells were fabricated with one-step method by using spin coating technique. These solar cells were in the structure form of FTO/compactTiO2/mesoporousTiO2/CH3NH3PbI3/Au. Different annealing temperatures were applied to investigate the effect of the annealing temperature on the properties of the fabricated solar cells since it lead to affect the crystallization degree of the CH3NH3PbI3 layer. Three temperatures were used for annealing the perovskite layer typically: 60°C, 80°C and 100°C and the best result found at 100 °C where the efficiency was 5.68%, FF = 0.55, Jsc = 12.637 mA/cm2 and Voc = 0.817 V.

Rapid fabrication of efficient P-type perovskite-sensitized solar cells using hot-air drying method

The successful development of organic-inorganic perovskite materials mainly based on CH3NH3PbI3 has improved the PCE of solar cells significantly and reduced the fabrication cost relatively. The majority of the researches focused on studying different ways of improving the performance and stability of perovskite devices with less attention paid to minimizing the time of fabrication. The reduction of fabrication time can simultaneously reduce the fabrication cost and boost the industrial manufacturing capability. In this work, we report a simple and rapid method of making CH3NH3PbI3 layer at ambient laboratory conditions and applying it for advancing the photon-to-electricity conversion efficiency of liquid-state CuO-based perovskite-sensitized solar cells. The whole fabrication process starting from electrodepositing CuO to sandwiching counter electrode entails less than 10 min and the device efficiency reaches up to 0.35% under one sun illumination.

An internally photoemitted hot carrier solar cell based on organic-inorganic perovskite

Hot carriers and their extraction have been demonstrated in organic-inorganic perovskites under transient condition. Unfortunately, there was no real device to harvest hot carriers under steady-state illumination yet due to the indistinguishable hot and cooled carriers in conventional sandwiched structure. Here we report a new designed architecture based on internally photoemitted hot carrier (IPHC) solar cell, whose active CH3NH3PbI3 layer is outside of the two collection electrodes with configuration of CH3NH3PbI3/Au/TiO2/FTO. Herein, the photoexcited hot electrons transfer ballistically from CH3NH3PbI3 layer to TiO2 via thin gold layer for electron collection. For the first time, the device we fabricated using this novel structure produces short circuit current of 5422 μA cm−2 under one sun (100 mW cm−2) illumination which demonstrates the efficient harvesting of hot electrons under steady-state sunlight illumination. The considerable efficient photocurrent showed by this new design opens an alternative approach for light-to-electricity conversion.

CH3NH3PbI3:MoS2 heterostructure for stable and efficient inverted perovskite solar cell

Organic-inorganic perovskite solar cells emerge as one of the most promising photovoltaic technology due to its high performances. Particularly, inverted perovskite device architecture, due to low temperature processing, have a great potential in commercialization. High-crystalline quality perovskite film and interfacial passivation are essential to yield high performance devices. In this work, we employ a simple strategy of using molybdenum disulfide (MoS2) as both the interfacial layer and the additive to prepare efficient PSCs. MoS2 as an additive in perovskite can form the CH3NH3PbI3:MoS2 heterostructure, resulting in the homogeneous perovskite film with larger crystal grains. In addition, MoS2 as the buffer layer (BL) between poly (3,4-ethylene dioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) and perovskite can prevent the decomposition of perovskite film by avoiding the direct contact with the hydrophilic PEDOT:PSS films. On tedious optimization, the champion device based on active layer of CH3NH3PbI3:MoS2 (10 v%) as well as employing MoS2 buffer layer shows a remarkable improvement in the power conversion efficiency (PCE) (from 15.29% to 18.31%) and a better stability, with 87% of the initial efficiency sustained after 20 days. Our finding herein provides a promising way to fabricate high efficiency and stable photovoltaic devices.

Modified HTL-induced efficiency enhancement for inverted perovskite solar cells

Abstract Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was doped by 3-(Cyclohexylamino)-2-hydroxy-1-propanesulfonic acid (CAPSO), leading to dramatic improvement of its conductivity and consequently efficiency enhancement in inverted perovskite solar cells (PSCs) based on PEDOT:PSS hole transport layer (HTL). Under the optimized CAPSO doping concentration, the conductivity of PEDOT:PSS film increased by about three orders of magnitude, and this is interpreted by the weakening of the coulombic attractions between PEDOT and PSS components induced by CAPSO. CAPSO doped PEDOT:PSS (PEDOT:PSS@CAPSO) was applied as HTL of PSCs devices based on CH3NH3PbI3 layers, leading to the best power conversion efficiency (PCE) of ~38% enhanced relative to those of the corresponding reference devices based on pristine PEDOT:PSS HTL. Scanning Kelvin probe microscopy (SKPM) results show that the work function of PEDOT@CAPSO matches well with the valence band of CH3NH3PbI3 absorbers. The research demonstrates that the zwitterion modified PEDOT:PSS could act as an outstanding hole transport material for fabricating high-efficient perovskite solar cells.

Structures and Properties of Higher-Degree Aggregates of Methylammonium Iodide toward Halide Perovskite Solar Cells

Organic–inorganic halide perovskite solar cells have been in the limelight in recent years due to their outstanding power conversion efficiency (PCE) and facile synthesis. Despite of the ever increasing PCE that astonishes the solar cell community, many fundamental structural and theoretical aspects remain elusive, which inhibit our understanding on this fascinating material. Methylammonium iodide (MAI) is one important precursor to fabricate the halide perovskite materials based on the prototypical CH3NH3PbI3. Some MAI might remain in the CH3NH3PbI3 layer, forming a MAI-rich layer that is considered strongly affecting the perovskite solar cell performance. Therefore it is helpful to take one step back to re-evaluate the structures of MAI that is overlooked in many perovskite solar cell studies. In this manuscript, we identify the alternative structures of MAI aggregates via the ab-initio calculations, including the monomeric, dimeric, trimeric, tetrameric, pentameric, hexameric, heptameric, octameric and decameric structures of MAI. These aggregate structures are proposed to act as a simplified, yet efficient model to represent the MAI-rich region in perovskite solar cells that are usually simulated using the computationally expensive slab model. We find that the aggregates of MAI are universally stabilized by the hydrogen bonds. We further evaluate these MAI aggregate structures via studying the interactions between the MAI aggregates and an experimentally-proven additive iodopentafluorobenzene (IPFB) as an example, and show that the iodine atoms in the MAI aggregates acting as potential charge traps could be passivated by the additive molecule. The present study provides an efficient modeling platform for the MAI-rich halide perovskite materials without high computational cost.

Interface engineering by using TiO2 nanocubic modifier in planar heterojunction perovskite solar cells

Abstract In this work we adopt a nanoscale TiO2 nanocubic particle as interfacial modifier between compact TiO2 layer and CH3NH3PbI3 layer. The TiO2 nanocubic modifier can passivate the defect states and suppress charge recombination at the TiO2/MAPbI3 interface. As a result, the photovoltaic performances of planar heterojunction perovskite solar cells were effectively boosted. Under standard air-mass 1.5 global illumination, the open-circuit voltage of solar cells with TiO2 nanocubic modifier was increased from 0.93 V to 1.02 V, and achieved a maximum power conversion efficiency of 14.70% with average value of 13.36%, which is 1.3 times higher than the solar cells based on without modified TiO2 layer (10.44%).

Ultrasonically sprayed-on perovskite solar cells-effects of organic cation on defect formation of CH3NH3PbI3 films

Methylammonium lead iodide (CH3NH3PbI3) based perovskite having low degrees of the disorder is of great interest for optoelectronic and photovoltaic applications. In this work, a layer of CH3NH3PbI3 was successfully prepared using an ultrasonically sprayed-nebulous method. Changes in structural and optical properties alongside with photo-induced charge separation and transportation behavior were systematically studied. The surface photovoltage spectra reveal a significant reduction of the density of deep defect states as the organic content was increased. It was observed that the measured values of Urbach energies decrease from 33.36 to 28.24 meV as the amount of organic content was increased to an optimum value. The best perovskite solar cells obtained using the sprayed-on approach exhibited a Jsc of 16.54 mA/cm2, a Voc of 0.99 V, and a FF of 62.4, resulting in an overall PCE of 10.09%.

Stable power output (PCE>19%) of planar perovskite solar cells with PbCl2 modification at the interface of SnO2/CH3NH3PbI3

Abstract Interfacial modification as a feasible strategy to improve the properties of perovskite solar cells (PSCs) has been widely studied in recent years. In this work, PbCl2 modification at the interface of SnO2/CH3NH3PbI3 was used for CH3NH3PbI3-based planar PSCs. The introduction of PbCl2 between SnO2 and CH3NH3PbI3 layers boosted the crystallization of perovskite film, which promoted the photovoltaic properties of corresponding PSCs. The open circuit voltage (VOC) and fill factor (FF) of the PbCl2-modified devices (1 mg/mL) were 1.11 V and 0.79, respectively, which were both higher than those of the reference devices without PbCl2 (1.04 V and 0.76). Moreover, a steady-state power output efficiency exceeding 19% was obtained for the PbCl2-modified devices (1 mg/mL), which implied that PbCl2 modification was an effective and low cost strategy for efficient PSCs.

A Rutile TiO2 Electron Transport Layer for the Enhancement of Charge Collection for Efficient Perovskite Solar Cells.

Interfacial charge collection efficiency has demonstrated significant effects on the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Herein, crystalline phase-dependent charge collection is investigated by using rutile and anatase TiO2 electron transport layer (ETL) to fabricate PSCs. The results show that rutile TiO2 ETL enhances the extraction and transportation of electrons to FTO and reduces the recombination, thanks to its better conductivity and improved interface with the CH3 NH3 PbI3 (MAPbI3 ) layer. Moreover, this may be also attributed to the fact that rutile TiO2 has better match with perovskite grains, and less trap density. As a result, comparing with anatase TiO2 ETL, MAPbI3 PSCs with rutile TiO2 ETL delivers significantly enhanced performance with a champion PCE of 20.9 % and a large open circuit voltage (VOC ) of 1.17 V.

A Rutile TiO2 Electron Transport Layer for the Enhancement of Charge Collection for Efficient Perovskite Solar Cells

AbstractInterfacial charge collection efficiency has demonstrated significant effects on the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Herein, crystalline phase‐dependent charge collection is investigated by using rutile and anatase TiO2 electron transport layer (ETL) to fabricate PSCs. The results show that rutile TiO2 ETL enhances the extraction and transportation of electrons to FTO and reduces the recombination, thanks to its better conductivity and improved interface with the CH3NH3PbI3 (MAPbI3) layer. Moreover, this may be also attributed to the fact that rutile TiO2 has better match with perovskite grains, and less trap density. As a result, comparing with anatase TiO2 ETL, MAPbI3 PSCs with rutile TiO2 ETL delivers significantly enhanced performance with a champion PCE of 20.9 % and a large open circuit voltage (VOC) of 1.17 V.

Preparation of high quality perovskite thin film in ambient air using ethylacetate as anti-solvent

Methylamine lead iodide (CH3NH3PbI3) perovskite thin film solar cell has attracted much attention due to its low cost and high photoelectric conversion efficiency. Preparation of high quality perovskite thin film is the key to obtain high conversion efficiency of solar cells. Here, the pinhole-free CH3NH3PbI3 layer with high coverage and smooth surface is prepared by the one-step solution method in air with ethylacetate as anti-solvent on an electron transport hybrid layer of TiO2 nanoparticles coated porous carbon. The effect of ethylacetate as anti-solvent on the quality of perovskite thin film is studied in detail by comparing with chlorobenzene and ethylether. The high saturation and humidity resistance of ethylacetate in air control the nucleation and growing kinetics of perovskite crystals during the spin coating process, which facilitates the formation of uniform pinhole-free perovskite thin films. The perovskite solar cell based on the prepared high quality thin film achieves the highest conversion efficiency of 17.41% in ambient air with a relative humidity of 35%, which is superior to the perovskite thin films prepared with chlorobenzene and ethylether (conversion efficiency of 10.80% and 10.20%). The higher light-to-electric conversion efficiency is due to high coverage of the pinhole-free perovskite thin film and good contact with the electron transport layer and the hole transport layer.

Applying BaTiO3-coated TiO2 core–shell nanoparticles films as scaffold layers to optimize interfaces for better-performing perovskite solar cells

In this paper, we replaced mesoporous TiO2 nanoparticles scaffold layers by BaTiO3-coated TiO2 core–shell nanoparticles films which obtained by treating pure mesoporous TiO2 layers with 1.0 wt% barium nitrate solution, successfully realized the aim of optimizing interfaces bonding at TiO2/CH3NH3PbI3. Ultrathin BaTiO3 shell layer can combine better with CH3NH3PbI3 layer so as to reduce the existence of carrier recombination centers. Moreover, better optical absorption and larger fill factor were obtained in this manner by the reason of larger CH3NH3PbI3 grain size and fewer crystal boundaries. Furthermore, photoluminescence spectra and electrochemical impedance spectroscopy verified that our core–shell scaffold material contributes to accelerate carrier separation and retard carrier recombination. As a result, average power conversion efficiency enhanced from 11.20 to 13.76% under ambient conditions, which realized almost a quarter improvement than the devices based on pure mesoporous TiO2 layers. Such results have a certain guiding effect on solving interface defects and carrier recombination.