MAPI Films Research Articles

Electric Field Effects in Hybrid Perovskites Studied via Picosecond Kerr Microscopy.

We present time-resolved Kerr rotation (TRKR) spectra in thin films of CH3NH3PbI3 (MAPI) hybrid perovskite using a unique picosecond microscopy technique at 4 K having a spatial resolution of 2 μm and temporal resolution of 1 ps, subjected to both an in-plane applied magnetic field up to 700 mT and an electric field up to 104 V/cm. We demonstrate that the obtained TRKR dynamics and spectra are substantially inhomogeneous across the MAPI films with prominent resonances at the exciton energy and interband transition of this compound. From the obtained quantum beating response as a function of magnetic field in the Voigt configuration, we also extract the inhomogeneity of the electron and hole Lande g-values and spin coherence time, T2*. We also report the TRKR dependence on both the applied magnetic field and electric field. From the change in the quantum beating dynamics, we found that T2* substantially decreases upon the application of an electric field. At the same time, from the induced spatial TRKR changes, we show that the electric field induced effects are caused by ion migration in the MAPI films.

Modulation of Ionically Generated Space Charge Effects at Hybrid Perovskite and Oxide Interfaces via Surface Modification

AbstractInterfacial space charges significantly influence transport and recombination of charge carriers in optoelectronic devices. Due to the mixed ionic‐electronic conducting properties of halide perovskites, not only electronic effects, but also ionic interactions at their interfaces need to be considered in the analysis of space charges. Understanding of these interactions and their control is currently missing. This study elucidates the ionic effects on space charge formation at the interface between methylammonium lead iodide (MAPI) and alumina, and its modulation through surface modification using organic molecules. Embedding insulating alumina nanoparticles within MAPI films leads to enhancement of the electronic conductivity. This effect is consistent with the formation of an interfacial inversion layer in MAPI and can only be explained on the basis of ionic interactions. Such an effect is attenuated by surface modification of the oxide via the chemisorption of organic molecules. Finally, the same trend is observed in solar cells, where reducing the potential of the distributed space charges within the composite active layer improves device performance. These findings emphasize the necessity of taking into account ionic interactions to control the space charge formation at interfaces involving mixed ionic‐electronic conductors, an essential aspect in the performance optimization of halide perovskite‐based devices.

Elucidating the Mechanism of Self-Healing in Hydrogel-Lead Halide Perovskite Composites for Use in Photovoltaic Devices.

Since the emergence of organometal halide perovskite (OMP) solar cells, there has been growing interest in the benefits of incorporating polymer additives into the perovskite precursor, in terms of both photovoltaic device performance and perovskite stability. In addition, there is interest in the self-healing properties of polymer-incorporated OMPs, but the mechanisms behind these enhanced characteristics are still not fully understood. Here, we study the role of poly(2-hydroxyethyl methacrylate) (pHEMA) in improving the stability of methylammonium lead iodide (MAPI, CH3NH3PbI3) and determine a mechanism for the self-healing of the perovskite-polymer composite following exposure to atmospheres of differing relative humidity, using photoelectron spectroscopy. Varying concentrations of pHEMA (0-10 wt %) are incorporated into a PbI2 precursor solution during the conventional two-step fabrication method for producing MAPI. It is shown that the introduction of pHEMA results in high-quality MAPI films with increased grain size and reduced PbI2 concentration compared with pure MAPI films. Devices based on pHEMA-MAPI composites exhibit an improved photoelectric conversion efficiency of 17.8%, compared with 16.5% for a pure MAPI device. pHEMA-incorporated devices are found to retain 95.4% of the best efficiency after ageing for 1500 h in 35% RH, compared with 68.5% achieved from the pure MAPI device. The thermal and moisture tolerance of the resulting films is investigated using X-ray diffraction, in situ X-ray photoelectron spectroscopy (XPS), and hard XPS (HAXPES). It is found that exposing the pHEMA films to cycles of 70 and 20% relative humidity leads to a reversible degradation, via a self-healing process. Angle-resolved HAXPES depth-profiling using a non-destructive Ga Kα source shows that pHEMA is predominantly present at the surface with an effective thickness of ca. 3 nm. It is shown using XPS that this effective thickness reduces with increasing temperature. It is found that N is trapped in this surface layer of pHEMA, suggesting that N-containing moieties, produced during reaction with water at high humidity, are trapped in the pHEMA film and can be reincorporated into the perovskite when the humidity is reduced. XPS results also show that the inclusion of pHEMA enhances the thermal stability of MAPI under both UHV and 9 mbar water vapor pressure.

The influence of thickness layers on the efficiency of MAPI solar cells

In this work, a modest method for creating Perovskite solar cells (PSCs) by recycling car batteries is used. Trying to get rid of some structures or materials which are harm to the environment. However, by reusing car batteries we will avoid the disposal of toxic battery materials and provide an alternative technique, readily-available Pb source for fabricating PSCs. Perovskite solar cells (PSCs) were prepared by two-step spin coating solution method on the FTO glass substrate. Lead iodide (PbI2) and methyl-ammonum iodide (CH3NH3I) used to form the structure of the precursor (CH3NH3PbI3). The photovoltaic performance of PSCs and the effect of chemical composition of perovskite layer on performance of PSCs was investigated. Characterization of PSCs by using X-ray diffraction, SEM and the effect of chemical composition on of MAPI films was achieved. It was found that the thickness ratio of (PbI2/MAI) with 3.0:1 have highest fill factor and maximum efficiency.

Compositional engineering and surface passivation for carbon-based perovskite solar cells with superior thermal and moisture stability

The inherent stability of perovskite absorbers towards environmental factors is a major limitation towards commercializing perovskite solar cells (PSCs). In this regard, MaPbI3 (MAPI) is engineered to attain thermal stability by incorporating Guanidinium iodide (GuI) and moisture stability by surface passivation using 5- amino valeric acid iodide (5-AVAI). The surface passivation of Gu modified MAPI, hereafter termed as GUMAPI, exhibits a 2D/3D perovskite interface, which, facilitates perovskite to attain high moisture and temperature stability. Various concentrations of 5-AVAI are used as the surface passivator. The stability of the surface-modified Gu doped MAPI films is studied thoroughly using time-dependent water contact angle measurements, in-situ temperature-dependent XRD analysis, and XRD studies of aged perovskite films under ambient conditions. 1AV films exhibit excellent temperature (>150 °C) and ambient stability (>59 days) when compared with control perovskite films (GUMAPI). The stability and performance of these perovskite films in a carbon-PSCs (CPSCs) architecture are evaluated by studying the current-voltage characteristics and assessing the device performance at various intervals. The 1AV-based CPSCs exhibit performance surpassing the control (GUMAPI) devices. A 9.0% increment is observed in the 1AV-based CPSCs compared to the GUMAPI-based CPSCs with an efficiency of 13.2% and a T80 lifetime of 93.2% without encapsulation.

Crystallization and Defect Chemistry Dual Engineering for MAPbI3 Perovskite Solar Cells with Efficiency Approaching 22%

Methylammonium lead triiodide (MAPI) has been the most commonly used light absorber layer for perovskite solar cells and also shows potentially high theoretical efficiency. However, the achievable efficiencies so far still lag behind those of their formamidinium- or mixed cation-based counterparts. In this work, the dual additives 2-mercaptopyridine (2-MP) and 1,2-dichlorobenzene (DCB) are applied to regulate the crystal orientation, yielding a high-crystal quality MAPI film and passivating the trap states of the film. Encouragingly, we are able to distinguish the efficacy of the two additives. DCB effectively reduced the size of colloidal clusters in the perovskite precursor, thus helping the wet film reach the critical concentration to initialize rapid nucleation. The resulting MAPI film exhibited extended grain size with a stronger grain orientation and smoother surface. With the subsequent introduction of 2-MP, the high crystal quality was maintained, and 2-MP interacted with uncoordinated Pb defects and passivated the related traps. The dual additive-processed devices exhibited the champion efficiency of 21.83% with a simultaneously high Jsc of 24.01 mA/cm2 and Voc of 1.15 V. This work provides a means to engineer the crystallization quality and defect chemistry toward efficient MAPbI3 perovskite solar cells.

Efficient Semitransparent Perovskite Solar Cells Based on Thin Compact Vacuum Deposited CH3NH3PbI3 Films

AbstractLead halide perovskite materials are promising candidates for the application of semitransparent solar cells due to their bandgap tunability and high device efficiencies. The high absorption coefficient of these materials, however, makes it difficult to attain high average visible transmittance values without compromising the power conversion efficiencies (PCEs). In this work, a co‐evaporation process is employed to fabricate thin (50 and 100 nm) methylammonium lead iodide (MAPI) perovskite films and integrate them in semitransparent perovskite solar cells (ST‐PSCs). Due to the compact nature of the thin MAPI films, the resultant fully vacuum and room temperature‐processed devices demonstrate high fill factor values approaching 80% and open‐circuit voltage values close to 1100 mV. As a result of this, the ST‐PSCs exhibit PCE's as high as 9% with a photopic average visible transmittance of the full device of 23%.

Band Bending at Hole Transporting Layer‐Perovskite Interfaces in n‐i‐p and in p‐i‐n Architecture

Interfaces between hybrid perovskite absorber and its adjacent charge‐transporting layers are of high importance for solar cells performance. Understanding their chemical and electronic properties is a key step in designing efficient and stable perovskite solar cells. In this work, the tapered cross‐section photoemission spectroscopy (TCS‐PES) method is used to study the methylammonium lead iodide (CH3NH3PbI3) (MAPI)‐based solar cells in two configurations, that is, in an inverted p–i–n and in a classical n–i–p architecture. It is revealed in the results that the MAPI film deposited once on the n‐type TiO2 and once on the p‐type NiOx substrates is neither an intrinsic semiconductor nor adapts to the dopant nature of the substrate underneath, but it is heavily n‐type doped on both substrates. In addition to that, the TCS‐PES results identify that the band bending between the MAPI film and the hole transporting layer (HTL) layer depends on the perovskite solar cells architecture. In particular, a band bending on the HTL side in the n–i–p and at the MAPI in the p–i–n architecture is found. The flat band of NiOx at the NiOx/MAPI interface can be explained by the Fermi level pinning of the NiOx at the interface.

Methylammonium Metal Iodide Perovskite Film Preparation from Gaseous and Liquid Sources

IntroductionPerovskite solar cells have attracted great expectation as next-generation solar cells since they were invented in 2009[1] due to their high power conversion efficiency (PCE), which is 25.2 % in 2020[2], and low cost. Now methylammonium lead iodide (MAPI, CH3NH3PbI3) is mainly used for a light-absorbing layer, but the toxicity of lead is the problem for commercial use. Recently, methylammonium bismuth iodide (MABI, (CH3NH3)3Bi2I9) is attracting attention for a new perovskite material because of its low toxicity, and high durability[3,4,5].For fabricating perovskite thin film, solution process is widely used due to its simplicity. However, it is impossible to use for the industrial scale. Therefore, development of a chemical vapor deposition (CVD) process is required for large-area fabrication of thin films. In this study, a novel CVD process to synthesize MAPI thin films from gaseous and liquid reactants is proposed. Thin films were also synthesized by solution process. The properties of MAPI and MABI were compared in terms of the component metals and the processes.ExperimentalSolution process— MAPI and MABI were synthesized respectively by dropping the precursor solution containing stoichiometric mixture of methylammonium iodide (MAI) and MI (M = Pb, Bi) on FTO substrates (10 ×10 ×1.1 mm3) set on the spin coater. The precursor solution was synthesized in reaction of 40 wt% MAI and MI (M = Pb, Bi) in -butyrolactone or N,N-dimethylformamide. After spin-coated, the solution film was annealed on the hot plate at 413 K.CVD process— As shown in Fig. 1, the reactor consisting of 3 parts, the iodide generation part, the mixing part, and the film deposition part, was used for CVD. In the iodide generation part, molten Pb was placed in a tube heated at 873 K, and 0.3 % HI in He was supplied for generating PbI2 vapor in Reaction (1).Pb + 2HI → PbI2 + H2 (1)PbI2 and HI were mixed with 10 % methylammonium (MA) in He in the mixing part and supplied for the film deposition part where MAPI film was synthesized on FTO substrates (8 ×10 ×1.1 mm3) coated with TiO2 at 413 K in Reaction (2).PbI2 + HI + MA → MAPI (2)The total pressure was approximately 2 kPa. HI and MA were supplied at a stoichiometric ratio of 3:1. Respective gases were supplied to inlets 1, 2, and 3 at flow rates of v 1 : v 2 : v 3 = 1 : 1 : 2.Obtained samples were analyzed by an X-ray diffractometer (Rigaku, Ultima), a UV-vis spectrophotometer (Shimadzu, UV-3100PC), and an SEM (Keyence, VE-7800).Results and DiscussionFig. 2 shows the film XRD patterns synthesized by the CVD and solution process. Both patterns show good agreement with MAPI reference pattern. MAPI thin film was successfully obtained by the proposed CVD process. The film synthesized by CVD has higher orientation and crystallinity. Stronger PbI2 peak is observed in the film synthesized by solution process. MAI, due to the lower molecular weight, may evaporate from the surface of solution while annealed.Fig. 3 shows the MAPI and MABI XRD patterns synthesized by the solution process. Full width at half maximum of main peak of MABI is greater than that of MAPI. Judged from the SEM images, the grain size of MABI is about 20 though MAPI is around 5 . The relatively less domain boundary in MABI thin film is expected to improve the power conversion efficiency.ConclusionsA novel CVD process from gaseous and liquid sources was developed and MAPI thin film was successfully obtained by the proposed process. More highly oriented and crystallized film were obtained by CVD process than solution process. MABI has higher crystallinity and its grain size was greater than what MAPI has.

Improving the stability of MAPbI3 films by using a new synthesis route

This paper reports results of a study on the impact that the synthesis method and the replacement of the methylammonium (MA) cation by the formamidinium (FA) cation have on both morphology and degradation of MAPbI3 (MAPI) films when these are exposed to environmental conditions.This study was conducted with samples deposited using different routes based on growth methods both in solution and thermal evaporation, including one step spin coating and two-steps new growth routes where in a first step a layer of PbI2 is deposited by conventional evaporation and then a second layer of MAI (methylammonium iodide) is deposited by dipping and CSS (close spaced sublimation) methods respectively.The study revealed that the stability of MAPI films is significantly improved when are deposited using the two-steps synthesis routes. Evidence was found explaining that this behavior could be attributed to the fact that this type of MAPI films, grow with large grain sizes and low density of native and structural defects, characteristics that lead to a reduction of the ionic migration initiated in grain boundaries regions, where the degradation process generally begins.

Defect/Interface Recombination Limited Quasi-Fermi Level Splitting and Open-Circuit Voltage in Mono- and Triple-Cation Perovskite Solar Cells.

Multication metal-halide perovskites exhibit desirable performance and stability, compared to their monocation counterparts. However, the study of the photophysical properties and the nature of defect states in these materials is still a challenging and ongoing task. Here, we study bulk and interfacial energy loss mechanisms in solution-processed MAPbI3 (MAPI) and (CsPbI3)0.05[(FAPbI3)0.83(MAPbBr3)0.17]0.95 (triple cation) perovskite solar cells using absolute photoluminescence (PL) measurements. In neat MAPI films, we find a significantly smaller quasi-Fermi level splitting than for the triple cation perovskite absorbers, which defines the open-circuit voltage of the MAPI cells. PL measurements at low temperatures (∼20 K) on MAPI films demonstrate that emissive subgap states can be effectively reduced using different passivating agents, which lowers the nonradiative recombination loss at room temperature. We conclude that while triple cation perovskite cells are limited by interfacial recombination, the passivation of surface trap states within the MAPI films is the primary consideration for device optimization.

Mechanisms of Spontaneous and Amplified Spontaneous Emission in CH3NH3PbI3 Perovskite Thin Films Integrated in an Optical Waveguide

In this paper, the physical mechanisms responsible for optical gain in ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{Pb}\mathrm{I}}_{3}$ (MAPI) polycrystalline thin films are investigated experimentally and theoretically. Waveguide structures composed by a MAPI film embedded in between PMMA and silica layers are used as an efficient geometry to confine emitted light in MAPI films and minimize the energy threshold for amplified spontaneous emission (ASE). We show that photogenerated exciton density at the ASE threshold is as low as $(2.4\ensuremath{-}12)\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.1em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, which is below the Mott transition density reported for this material and the threshold transparency condition deduced with the free-carrier model. Such a low threshold indicates that the formation of excitons plays an important role in the generation of optical gain in MAPI films. The rate-equation model including gain is incorporated into a beam-propagation algorithm to describe waveguided spontaneous emission and ASE in MAPI films, while using the optical parameters experimentally determined in this work. This model is a useful tool to design active photonic devices based on MAPI and other metal-halide semiconductors.

The growth of methylammonium lead iodide perovskites by close space vapor transport.

Vapor deposition processes have shown promise for high-quality perovskite solar cells with potential pathways for scale-up to large area manufacturing. Here, we present a sequential close space vapor transport process to deposit CH3NH3PbI3 (MAPI) perovskite thin films by depositing a layer of PbI2 then reacting it with CH3NH3I (MAI) vapor. We find that, at T = 100 °C and pressure = 9 torr, a ∼225 nm-thick PbI2 film requires ≥125 minutes in MAI vapor to form a fully-reacted MAPI film. Raising the temperature to 160 °C increases the rate of reaction, such that MAPI forms within 15 minutes, but with reduced surface coverage. The reaction kinetics can be approximated as roughly first-order with respect to PbI2, though there is evidence for a more complicated functional relation. Perovskite films reacted at 100 °C for 150 minutes were fabricated into solar cells with an SLG/ITO/CdS/MAPI/Spiro-OMeTAD/Au structure, and a device efficiency of 12.1% was achieved. These results validate the close space vapor transport process and serve as an advance toward scaled-up, vapor-phase perovskite manufacturing through continuous vapor transport deposition.

A modified high-temperature vapour deposition technique for fabricating $$\hbox {CH}_{3}\hbox {NH}_{3}\hbox {PbI}_{3}$$ thin films under an ambient atmosphere

A modified two-step deposition technique was performed by vapour depositing methylammonium iodide (MAI) on lead iodide $$(\hbox {PbI}_{2})$$ films to fabricate good quality methylammonium lead iodide (MAPI) thin films under an ambient atmosphere, and their properties were compared with conventional two-step solution processed MAPI thin films. Scanning electron microscopy results depicted that the MAI vapour-processed films have a uniform coverage and planar surface compared with the non-uniformly distributed granule-like morphology of the solution-processed MAPI film. X-ray diffraction results confirm that the vapour-processed films have better crystallinity compared to the conventional solution-processed MAPI thin films. An enhancement in the optical absorption and emission was observed for the vapour-processed films. The higher processing temperature of the modified-vapour deposition eliminates the effect of moisture during the ambient atmosphere processing of the MAPI films.

Room-Temperature Cubic Phase Crystallization and High Stability of Vacuum-Deposited Methylammonium Lead Triiodide Thin Films for High-Efficiency Solar Cells.

Methylammonium lead triiodide (MAPI) has emerged as a high-performance photovoltaic material. Common understanding is that at room temperature, it adopts a tetragonal phase and it only converts to the perfect cubic phase around 50-60 °C. Most MAPI films are prepared using a solution-based coating process, yet they can also be obtained by vapor-phase deposition methods. Vapor-phase-processed MAPI films have significantly different characteristics than their solvent-processed analogous, such as relatively small crystal-grain sizes and short excited-state lifetimes. However, solar cells based on vapor-phase-processed MAPI films exhibit high power-conversion efficiencies. Surprisingly, after detailed characterization it is found that the vapor-phase-processed MAPI films adopt a cubic crystal structure at room temperature that is stable for weeks, even in ambient atmosphere. Furthermore, it is demonstrated that by tuning the deposition rates of both precursors during codeposition it is possible to vary the perovskite phase from cubic to tetragonal at room temperature. These findings challenge the common belief that MAPI is only stable in the tetragonal phase at room temperature.

Air-Stable Methylammonium Lead Iodide Perovskite Thin Films Fabricated via Aerosol-Assisted Chemical Vapor Deposition from a Pseudohalide Pb(SCN)2 Precursor

Ambient-air-stable methylammonium lead iodide (MAPI) perovskite thin films have been fabricated via one-step aerosol-assisted chemical vapor deposition (AACVD) from a pseudohalide Pb(SCN)2 precursor. We compare both the bulk and surface properties of the perovskite films grown using AACVD with those made by the widely used spin-coating method. Films with larger grain sizes and much better stability in ambient air can be obtained by AACVD. By addition of excess MAI to the precursor solution, MAPI films with negligible PbI2 impurities, as determined by X-ray diffraction, are obtained. The AACVD-grown MAPI films retain high phase purity with limited PbI2 formation after aging in air for approximately one month. The films exhibit an optical bandgap energy of ca. 1.55 eV and the expected nominal bulk stoichiometry (within error). In addition to probing bulk properties, we utilize X-ray photoelectron spectroscopy (XPS) to scrutinize the surface characteristics in detail. We find that the use of excess MAI resul...

Improvement Properties of Hybrid Halide Perovskite Thin Films Prepared by Sequential Evaporation for Planar Solar Cells.

Thin films of CH3NH3PbI3 and (NH2)2CHPbI3 (from now on abbreviated as MAPI and FAPI respectively), with perovskite structure were prepared by sequential evaporation of lead iodide (PbI2) and methylammonium iodide (MAI) or formamidinium iodide (FAI), with special emphasis on the optimization of its optical, morphologic, and structural properties. For this, the evaporation process was automatically controlled with a system developed using virtual instrumentation (VI) that allows electronic control of both evaporation sources temperature and precursors deposition rates, using proportional integral derivative (PID) and pulse width modulation (PWM) control algorithms developed with the LabView software. Using X-ray diffraction (XRD), information was obtained regarding the phase and crystalline structure of the studied samples as well as the effect of the main deposition parameters on crystallite size and microstrain. We also studied the influence of the main deposition parameters on the optical and morphological properties through measurements of spectral transmittance and scanning electron microscopy (SEM) respectively. It was found that the implemented method of sequential evaporation allows preparing, with a high degree of reproducibility, single phase MAPI and FAPI thin films with appropriate properties to be used as active layer in hybrid solar cells. The applicability of MAPI and FAPI thin films as active layer in photovoltaic devices has been demonstrated by using them in solar cells with structure: FTO/ZnO/MAPI(or FAPI)/P3HT/Au.

Enhance the performance of ZnO-based perovskite solar cells under ambient conditions

The ETL layer is used to transport electrons and block holes in the perovskite solar cell (PSC), and the uniformity of the dense layer affects the open circuit voltage (Voc) of the battery. The PSC open circuit voltage prepared by the solution method was 0.68 V, and the open circuit voltage of the PSC prepared by the sol method was remarkably improved to 0.95 V. The quality of the perovskite layer is critical for obtaining high-performance perovskite solar cells (PSC). In the process of preparing PSC by sequential deposition, the MAI solution was formed by IPA-n-hexane instead of isopropyl alcohol (IPA) as a solvent to grow CH3NH3PbI3(MAPI). The MAPI prepared by the mixed solvent was characterized by scanning electron microscopy (SEM). The mixed solvent inhibited the Oswald ripening process, and the perovskite layer showed a uniform and dense morphology. The PL characterization implied that the MAPI film with low defect concentration, which prepared from the mixed solvent. Compared to the single solvent PSC (PCE = 4.2%), the efficiency was significantly improved by 1.5 times to 6.2%. This study provides the possibility to prepare ZnO-based high-efficiency solar cell devices in the air.

Perovskite/Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] Bulk Heterojunction for High-Efficient Carbon-Based Large-Area Solar Cells by Gradient Engineering.

The performance of low-temperature carbon-based perovskite solar cells (C-PSCs) with high commercial potential was hampered by the inferior interface between the absorber and carbon electrode. In this work, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) was dissolved in an antisolvent for spin-coating perovskite (CH3NH3PbI3, MAPI) films, which was applied to modify both the MAPI films and the interface between the MAPI layer and carbon electrode by gradient engineering. Finally, the C-PSCs based on MAPI-PTAA gradient bulk heterojunction films achieved a power conversion efficiency of 13.0% with an active area of 1 cm2, 26% higher than that of pristine MAPI cells, because of the passivated trap states, accelerated hole extraction, and improved crystalline properties in absorber films.

Novel Physical Vapor Deposition Approach to Hybrid Perovskites: Growth of MAPbI3 Thin Films by RF-Magnetron Sputtering

Solution-based methods represent the most widespread approach used to deposit hybrid organic-inorganic perovskite films for low-cost but efficient solar cells. However, solution-process techniques offer limited control over film morphology and crystallinity, and most importantly do not allow sequential film deposition to produce perovskite-perovskite heterostructures. Here the successful deposition of CH3NH3PbI3 (MAPI) thin films by RF-magnetron sputtering is reported, an industry-tested method to grow large area devices with precisely controlled stoichiometry. MAPI films are grown starting from a single-target made of CH3NH3I (MAI) and PbI2. Films are single-phase, with a barely detectable content of unreacted PbI2, full surface coverage and thickness ranging from less than 200 nm to more than 3 μm. Light absorption and emission properties of the deposited films are comparable to as-grown solution-processed MAPI films. The development of vapor-phase deposition methods is of interest to advance perovskite photovoltaic devices with the possibility of fabricating perovskite multijunction solar cells or multicolor bright light-emitting devices in the whole visible spectrum.