Lead Iodide Perovskite Thin Films Research Articles

Real-time detection of aging status of methylammonium lead iodide perovskite thin films by using terahertz time-domain spectroscopy

The inadequate stability of organic–inorganic hybrid perovskites remains a significant barrier to their widespread commercial application in optoelectronic devices. Aging phenomena profoundly affect the optoelectronic performance of perovskite-based devices. In addition to enhancing perovskite stability, the real-time detection of aging status, aimed at monitoring the aging progression, holds paramount importance for both fundamental research and the commercialization of organic–inorganic hybrid perovskites. In this study, the aging status of perovskite was real-time investigated by using terahertz time-domain spectroscopy. Our analysis consistently revealed a gradual decline in the intensity of the absorption peak at 0.968 THz with increasing perovskite aging. Furthermore, a systematic discussion was conducted on the variations in intensity and position of the terahertz absorption peaks as the perovskite aged. These findings facilitate the real-time assessment of perovskite aging, providing a promising method to expedite the commercialization of perovskite-based optoelectronic devices.Graphical

Lead-free methyl ammonium tin iodide perovskite thin film growth in single step via plasma enhanced chemical vapour deposition technique and its optoelectronic properties

In the present work, lead free methyl ammonium tin iodide (CH3NH3SnI3 or MASnI3) perovskite thin films have been deposited via single step plasma enhanced chemical vapour deposition (PECVD) technique. In our earlier work, we reported lead based methyl ammonium lead iodide (CH3NH3PbI3 or MAPbI3) perovskite thin film deposition in 2-step, using sputtering technique for the PbI2 thin films and PECVD technique for CH3NH3I (MAI) thin films. CH3NH3I thin films were deposited using PECVD technique in the earlier study. Similarly, CH3NH3SnI3 perovskite thin films are deposited in this work using PECVD technique in single step. Lead is substituted with tin due to its toxic behaviour, environmental and health related issues. CH3NH3SnI3 perovskite is doped n-type via changing the molar ratio of SnI2 and CH3NH3I. SnI2/CH3NH3I ratio is changed from 0.33 to 2 to study the n-type doping of CH3NH3SnI3 perovskite. Deposited CH3NH3SnI3 perovskite thin films are deposited over p-type silicon wafer to make n-type doped n-CH3NH3SnI3/p-Si heterojunction photodiode.

Triple-junction perovskite-perovskite-silicon solar cells with power conversion efficiency of 24.4.

The recent tremendous progress in monolithic perovskite-based double-junction solar cells is just the start of a new era of ultra-high-efficiency multi-junction photovoltaics. We report on triple-junction perovskite-perovskite-silicon solar cells with a record power conversion efficiency of 24.4%. Optimizing the light management of each perovskite sub-cell (∼1.84 and ∼1.52 eV for top and middle cells, respectively), we maximize the current generation up to 11.6 mA cm-2. Key to this achievement was our development of a high-performance middle perovskite sub-cell, employing a stable pure-α-phase high-quality formamidinium lead iodide perovskite thin film (free of wrinkles, cracks, and pinholes). This enables a high open-circuit voltage of 2.84 V in a triple junction. Non-encapsulated triple-junction devices retain up to 96.6% of their initial efficiency if stored in the dark at 85 °C for 1081 h.

Development of Halide Perovskites for Solar Cell Applications

Halide perovskites have shown great potential for high efficiency solar cells, owing to their excellent optical and electrical properties. In this work, the preliminary development of methylammonium lead iodide (MAPbI3) perovskite thin film and planar negative-intrinsic-positive (n-i-p) thin film-based perovskite solar cell were demonstrated. The MAPbI3 thin film was successfully prepared using the anti-solvent assisted “one-step” solution deposition method. Ultraviolet-Visible (UV-Vis) absorbance analysis on the MAPbI3 thin film indicated the presence of broad absorption over the visible region from 450 to 800 nm. The Tauc plot bandgap energy was determined as 1.535 eV. Atomic force microscope (AFM) imaging evidenced uniform and smooth perovskite film with average grain size of 90 nm and root-mean-square roughness of 3.3746 nm. The current-voltage (I-V) curve of the perovskite solar cell demonstrated a linear relationship and inferior photovoltaic performance, hence the design and fabrication process of the solar cell necessitate further investigations and improvements.

Static anti-solvent treatment on lead iodide in two-step deposition of methylammonium lead iodide perovskite thin films

Static anti-solvent treatment is rarely employed for perovskite thin film fabrication, even though this method is dependent only on fewer thin film growth parameters as compared to the dynamic anti-solvent application. Thus, studies on the influence of static anti-solvent treatment on the properties of perovskite thin films is important to gain insight to the growth processes, which is very scarce as well. In this study, we investigate the static anti-solvent treatment to tailor the morphology of Lead Iodide (PbI2) thin films for the fabrication of precursor-free Methylammonium Lead Iodide (MAPI) perovskite thin films through the two-step deposition method using Chlorobenzene as an anti-solvent. Remarkable influence of the anti-solvent loading time on the film morphology of PbI2 and MAPI thin films is observed. The crystallinity of PbI2 decreases upon increasing the anti-solvent loading time. A complete conversion of the precursors to MAPI along with the largest grain size are attained even at short loading times, ∼5s. Grain size does not increase considerably at higher loading times. Linear absorption studies on MAPI thin films show an increase in the Urbach energy with an increase in the loading time, which indicates an increase in the defect density. The increase in defect density with anti-solvent loading time is attributed to the concurrent decrease in the crystallinity of the PbI2 thin film. Steady-state and time-resolved photoluminescence (PL) studies performed on the MAPI thin films show highest PL intensity and life time at an optimum anti-solvent loading time (∼5s), which arises due to the trade off between largest grain size and lowest defect density. These observations not only highlights the need for an optimum crystallinity in the PbI2 thin films for the fabrication of superior quality MAPI thin films but also infers an optimum static anti-solvent loading time as the increase in grain size and life time enhances the device performance while an increase in defect density degrades the performance.

Impact of gamma rays on the structural, optical, and current-voltage characteristics of CuPbI3/p-Si heterojunctions

Copper lead iodide (CuPbI3) perovskite thin films were spin-coated on p-type silicon (p-Si) substrates to manufacture CuPbI3/p-Si heterojunctions. A Co-60 gamma source has been used to examine the influence of gamma exposure doses of 0–100 kGy on the nanostructural, electrical, morphological, and optical, properties of the CuPbI3/p-Si heterostructure. The X-ray diffraction (XRD) consequences showed an enhancement in crystalline naturre and confirmed the hexagonal structure of the prepared thin films. Field emission scanning electron microscopy (FESEM) images revealed that the average grain size decreased (92–56 nm) up to 50 kGy, and the small particles agglomerated with a further increase in the gamma dose. The photoluminescence (PL) results of the deposited sample revealed only one broad bandgap peak. However, the PL spectra of the gamma ray-exposed samples exhibited induced defect emission near the valence band edge. The I–V properties revealed the charge transportation mechanism in the heterojunction, and the impacts of different gamma exposure doses on the electrical characteristics of the fabricated CuPbI3/p-Si heterojunction were investigated. Electrical parameters, such as the barrier potential, saturation current, series resistance, and ideality factor (IF) of the CuPbI3/p-Si heterostructure changed with the gamma irradiation dose owing to interfacial inhomogeneities, induced defect concentration, charge accumulation at the interface, and barrier thickness.

Electrical properties and defect analysis of MAPbI3 thin films grown on TiO2 layer through a two-step drying process

We studied the electrical properties and defect states of methylammonium lead iodide perovskite (MAPbI3) thin film grown onto the TiO2 layer at a temperature of 120 °C via a two-step drying process. The TiO2 layer with thickness of 20 nm were formed on fluorine doped tin oxide/glass at 120 °C via atomic layer deposition. The MAPbI3 thin film showed α-phase structure with band gap energy of about 1.61 eV. For the MAPbI3/TiO2 with Ag top and bottom electrodes, the resistance switching phenomena were enhanced compared to the MAPbI3 film without the TiO2 layer. In the MAPbI3/TiO2, two deep level states of E1(Ec-0.38 eV) and H2 (Ev+0.82 eV) appeared from deep level transient spectroscopy measurements. The defect states of E1 and H2 are related to iodine interstitial (Ii) and iodine antisite (IPb), respectively. In the MAPbI3/TiO2, the defect of Ii appeared as the ionized states of Ii+ or Ii−, so that it was found that the defect state of Ii caused the MAPbI3/TiO2 to have the resistance random access memory property by the migration of the ionized states.

Contactless quasi-steady-state photoconductance (QSSPC) characterization of metal halide perovskite thin films

We apply the contactless quasi-steady-state photoconductance (QSSPC) method to co-evaporated methyl ammonium lead iodide (MAPbI3) perovskite thin-films. Using an adapted calibration for ultralow photoconductances, we extract the injection-dependent carrier lifetime of the MAPbI3 layer. The lifetime is found to be limited by radiative recombination at the high injection densities applied during the QSSPC measurement, enabling the extraction of the electron and hole mobility sum in the MAPbI3 using the known coefficient of radiative recombination of MAPbI3. Combining the QSSPC measurement with transient photoluminescence measurements, performed at much lower injection densities, we obtain the injection-dependent lifetime curve over several orders of magnitude. From the resulting lifetime curve, we determine the achievable open-circuit voltage of the examined MAPbI3 layer.

Correction to: Experimental and theoretical analysis of doping methylammonium lead iodide perovskite thin films with barium and magnesium

Correction to: Experimental and theoretical analysis of doping methylammonium lead iodide perovskite thin films with barium and magnesium

Controlled growth of perovskite layers with volatile alkylammonium chlorides.

Controlling the crystallinity and surface morphology of perovskite layers by methods such as solvent engineering1,2 and methylammonium chloride addition3-7 is an effective strategy for achieving high-efficiency perovskite solar cells. In particular, it is essential to deposit α-formamidinium lead iodide (FAPbI3) perovskite thin films with few defects due to their excellent crystallinity and large grain size. Here we report the controlled crystallization of perovskite thin films with the combination of alkylammonium chlorides (RACl) added to FAPbI3. The δ-phase to α-phase transition of FAPbI3 and the crystallization process and surface morphology of the perovskite thin films coated with RACl under various conditions were investigated through in situ grazing-incidence wide-angle X-ray diffraction and scanning electron microscopy. RACl added to the precursor solution was believed to be easily volatilized during coating and annealing owing to dissociation into RA0 and HCl with deprotonation of RA+ induced by RA⋯H+-Cl- binding to PbI2 in FAPbI3. Thus, the type and amount of RACl determined the δ-phase to α-phase transition rate, crystallinity, preferred orientation and surface morphology of the final α-FAPbI3. The resulting perovskite thin layers facilitated the fabrication of perovskite solar cells with a power-conversion efficiency of 26.08% (certified 25.73%) under standard illumination.

Formamidinium Lead Iodide Perovskite Thin Films Formed by Two-Step Sequential Method: Solvent-Morphology Relationship.

Thin films made of formamidinium lead iodide (FAPbI3) perovskites prepared by a two-step sequential deposition method using various solvents for formamidinium iodide (FAI) - isopropanol, n-butanol and tert-butanol, were studied with the aim of finding a correlation between morphology and solvent properties to improve film quality. They were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and their photophysical properties were studied by means of absorption and photoluminescence (PL) spectroscopies. XRD patterns, absorption and PL spectra proved α-phase formation for all selected solvents. An excessive amount of PbI2 found in perovskite films prepared with n-butanol indicates incomplete conversion. Thin film morphology, such as grain and crystallite size, depended on the solvent. Using tert-butanol, thin films with a very large grain size of up to several micrometers and with preferred crystallite orientation were fabricated. The grain size increased as follows: 0.2-0.5, 0.2-1 and 2-5 µm for isopropanol, n-butanol and tert-butanol, respectively. A correlation between the grain size and viscosity, electric permittivity and polarizability of the solvent could be considered. Our results, including fabrication of perovskite films with large grains and fewer grain boundaries, are important and of interest for many optoelectronic applications.

Numerical modelling of the effect of MAPI3 thin film on ITO/TiO2/MEH-PPV/Au solar cell

Considering the temporary ecological challenges confronting our global milieu, the imperative to transition towards sustainable and conscientious methodologies looms as an unequivocal necessity. As purveyors of scientific inquiry our mandate is to meticulously explore a plethora of alternatives, liberating ourselves from the shackles of deleterious energy sources. We are investigating the value of semiconducting polymer-based solar cells in this work from a material science perspective because they are quite affordable to synthesize and have demonstrated some encouraging results, due to its notable benefits in photovoltaic (PV) applications, such as its high absorption coefficients, excellent charge carrier mobility, and favorable blend morphology with acceptor materials, which all contribute to improved device performance. We are using poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) in this study. In order to investigate the impact of the Methylammonium Lead Iodide Perovskite (MAPI3) thin film on the performance of the ITO/TiO2/MEH-PPV/Au solar cell, a numerical simulation was carried out using SCAPS-1D. Open circuit voltage (Voc), density of short circuit (Jsc), fill factor (FF), efficiency (η), and other solar cell metrics were measured and analyzed, with special emphasis to device inputs and the ensuing improvements. The performance of the MEH-PPV/TiO2 solar cell has been enhanced by the addition of MAPI3, resulting in a noteworthy 14% efficiency boost. These modelling results can be very useful for a better understanding and control of this type of solar cells.

Role of A‐Site Composition in Charge Transport in Lead Iodide Perovskites

As the power conversion efficiency and stability of solar cells based on metal halide perovskites continue to improve, the community increasingly relies on compounds formed of mixed cations and mixed halides for the highest performing devices. The result is that device engineers now have a potentially infinite number of compositions to choose from. While this has provided a large scope for optimization, it has increased complexity of the field, and the rationale for choosing one composition over another remains somewhat empirical. Herein, the distribution of electronic properties for a range of lead iodide perovskite thin films is mapped. The relative percentages of methylammonium, formamidinium, and cesium are varied, and the electronic properties are measured with time‐resolved microwave conductivity, a contactless technique enabling extraction of electronic properties of isolated films of semiconductors. It is found a small amount of Cs leads to larger carrier mobilities and longer carrier lifetimes and that compositions with a tolerance factor close to 0.9 generally show lower performance that those closer to 0.8 or 1.0.

Photoluminescence Dynamics of MAPI Perovskite Films Induced by Lateral Electric Field

The time‐dependent behavior of perovskite devices is one of the limiting factors for wide application of these materials in sandwich‐type or lateral optoelectronic device architectures. Despite abundant research on the topic, the exact mechanisms underlying the dynamics of device performance remain elusive. Herein, photoluminescence (PL) and electric field‐induced second harmonic microscopy techniques are combined to image and identify voltage‐induced lateral dynamic processes in methylammonium lead iodide perovskite thin films. A sequence of voltage‐induced dynamic steps is observed: i) Appearance of a short‐lived bright PL next to the positive electrode; ii) formation of a moving dark PL front; iii) emergence and blinking of bright PL spots; iv) growth and subsequent decay of the bright PL spots after voltage turn off. This behavior is explained by proposing a model of varying spatial distribution of inter‐electrode electric field and the presence of two types of PL quenching defects.

Probing the defects states in MAPbI3 perovskite thin films through photoluminescence and photoluminescence excitation spectroscopy studies

The luminescence properties of methylammonium lead iodide (MAPbI3) perovskite thin films deposited on corning 1737 glass substrates are studied using photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy. From the PL spectra analysis, it is realized that there are two emission peaks, a high-intensity peak at 1.58 eV (~783 nm) and a smaller shoulder peak at 1.64 eV (~754 nm) in the bandgap energy region. The peak at ~1.64 eV corresponds to the bandgap of MAPbI3, whereas the high-intensity peak at photon energy ~1.58 eV is due to the presence of shallow trap states. The calculated optical bandgap energy 1.58 ± 0.01 eV is close to the reported bandgap energy 1.60–1.61 eV and consistent with the PL peak position. The slight difference in bandgap value is due to shallow defect states in MAPbI3 films. The slow decay of photocurrent observed in the transient photocurrent measurements further confirms the presence of shallow trap states in MAPbI3 perovskite.

Stability Improvement of Methylammonium Lead Iodide Perovskite Thin Films by Bismuth Doping

Perovskites have been in the spotlight in the field of solar cells due to their high efficiency and their low cost of materials and fabrication processes. Perovskite solar cells (PSCs) have shown an efficiency of up to 25%. Nevertheless, PSCs have some drawbacks such as rapid degradation in ambient conditions. To improve PSC stability, lead is usually replaced with bismuth. In this article, we report the results when doping the methylammonium lead iodide (CH3NH3)PbI3, aka MAPbI3, with different bismuth quantities. The incorporation of bismuth into the lattice leads to a remarkable change in optoelectronics and morphological structure. Substituting lead atoms with 2% bismuth improves some characteristics of MAPbI3 layers, such as removing pinholes and increasing crystallite size and optical absorption. Furthermore, bismuth doping improves the stability of pure MAPbI3 layers, which after 4 weeks exhibits higher degradation compared to bismuth-doped MAPbI3 samples, which remain stable after that period.

Discovering equations that govern experimental materials stability under environmental stress using scientific machine learning

While machine learning (ML) in experimental research has demonstrated impressive predictive capabilities, extracting fungible knowledge representations from experimental data remains an elusive task. In this manuscript, we use ML to infer the underlying differential equation (DE) from experimental data of degrading organic-inorganic methylammonium lead iodide (MAPI) perovskite thin films under environmental stressors (elevated temperature, humidity, and light). Using a sparse regression algorithm, we find that the underlying DE governing MAPI degradation across a broad temperature range of 35 to 85 °C is described minimally by a second-order polynomial. This DE corresponds to the Verhulst logistic function, which describes reaction kinetics analogous to self-propagating reactions. We examine the robustness of our conclusions to experimental variance and Gaussian noise and describe the experimental limits within which this methodology can be applied. Our study highlights the promise and challenges associated with ML-aided scientific discovery by demonstrating its application in experimental chemical and materials systems.

Solvent Effects on the Structural and Optical Properties of MAPbI3 Perovskite Thin Film for Photovoltaic Active Layer

Controlling the crystallinity, homogeneity, and surface morphology is an efficient method of enhancing the perovskite layer. These improvements contribute toward the optimization of perovskite film morphology for its use in high-performance photovoltaic applications. Here, different solvents will be used in order to process the perovskite precursor, to improve the interfacial contacts through generating a smooth film and uniform crystal domains with large grains. The effect that the solvent has on the optical and structural properties of spin-coated methyl ammonium lead iodide (MAPbI3) perovskite thin films prepared using a single-step method was systematically investigated. The spin-coating parameters and precursor concentrations of MAI and PbI2 were optimized to produce uniform thin films using the different solvents N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). The effect that the solvent has on the morphology of the MAPbI3 films was examined to determine how the materials can be structurally altered to make them highly efficient for use in perovskite hybrid photovoltaic applications. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) results show that the synthesized MAPbI3 films prepared using DMSO, DMF, and GBL exhibit the best crystallinity and optical characteristics (photoluminescence (PL)), respectively, of the prepared films. The optical properties resulting from the noticeable improvement PL of the films can be clearly correlated with their crystallinity, depending on the solvents used in their preparation. The film prepared in DMSO shows the highest transmittance and the highest bandgap energy of the prepared films.

Microstructure of Methylammonium Lead iodide Perovskite Thin Films: A Comprehensive Study of the Strain and Texture

AbstractControlling the microstructure of hybrid halide perovskite thin films is essential for optimizing their performance in optoelectronic devices. It is well established that the strain state of the perovskite layer affects its stability. Likewise, the orientation of the perovskite lattice is a determining parameter as these materials have shown pronounced anisotropies in their physical and mechanical properties. In this work, the authors focus on the understanding of the mechanisms that govern the strain and texture observed in MAPbI3 thin films deposited on various oxide substrates. A thorough study of the evolution of the strain of the perovskite layer upon cooling down to room temperature from the crystallization temperature (100 °C) shows an essentially relaxed behavior of the perovskite layers. This result contradicts the commonly accepted hypothesis according to which MAPbI3 layers synthesized above ambient temperature are strained due to the large mismatch in the thermal expansion coefficients of the perovskite and its substrate. The texture in MAPbI3 layers is investigated by means of synchrotron full‐field diffraction X‐ray microscopy. This technique allows the direct observation of the [hh0] and [00l]‐oriented domains at the origin of the observed textures, demonstrating both their twin and ferroelastic nature. The stability of the different domain orientations is investigated by DFT calculations, illustrating the determining role of the chemical environment at the film‐substrate interface. PbI2‐ terminated surfaces are found to favor the [hh0] orientations while for MAI‐terminated ones, both [hh0] and [00l] domains are equally stabilized. The different results constitute an important step of clarification and understanding from the perspective of controlling the microstructure of perovskite layers.

Short Photoluminescence Lifetimes Linked to Crystallite Dimensions, Connectivity, and Perovskite Crystal Phases.

Time-correlated single photon counting has been conducted to gain further insights into the short photoluminescence lifetimes (nanosecond) of lead iodide perovskite (MAPbI3) thin films (∼100 nm). We analyze three different morphologies, compact layer, isolated island, and connected large grain films, from 14 to 300 K using a laser excitation power of 370 nJ/cm2. Lifetime fittings from the Generalized Berberan-Santos decay model range from 0.5 to 6.5 ns, pointing to quasi-direct bandgap emission despite the three different sample strains. The high energy band emission for the isolated-island morphology shows fast recombination rate centers up to 4.8 ns–1, compared to the less than 2 ns–1 for the other two morphologies, similar to that expected in a good quality single crystal of MAPbI3. Low-temperature measurements on samples reflect a huge oscillator strength in this material where the free exciton recombination dominates, explaining the fast lifetimes, the low thermal excitation, and the thermal escape obtained.