Triple-Cation Mixed-Halide Perovskite Research Articles

Synergetic Optimization of Upper and Lower Surfaces of the SnO2 Electron Transport Layer for High-Performance n-i-p Perovskite Solar Cells.

The SnO2 electron transport layer (ETL) has been recognized as one of the most effective protocols for achieving high-efficiency perovskite solar cells (PSCs). To date, most research has primarily focused on the modification of the upper surface of SnO2 ETL films. The lower surface of the SnO2 film, which directly influences the film formation of solution-processed SnO2, is equally important but receives relatively less attention. Herein, we present a synergetic optimization approach involving the deposition of aluminum oxide (AlOx) via atomic layer deposition (ALD) as a buffer layer and the incorporation of rubidium acetate (RbAc) as an upper surface passivation additive. This process leads to a conformal coating of SnO2 nanoparticles, improved electrical performance, and higher-quality perovskite crystals. As a result, with this composite ETL film, the power conversion efficiency (PCE) reached 22.41 from 20.77%. Further modification with p-butyl iodide (BAI) on the perovskite upper surface increased the champion PCE to 23.32%, with a voltage loss of 0.41 V, ranking among the lowest values for the triple-cation mixed-halide perovskite absorber (1.58 eV). Importantly, the perovskite solar cells remained 87.30% of its initial performance after 14 days of aging and exhibited photostability under long-term UV (254 nm) illumination.

Improved stability and efficiency of inverted triple-cation mixed-halide perovskite solar cells with CsI-modified NiOx hole transporting layer

Addressing the critical challenge of mitigating defect generation and enhancing the extended durability of perovskite solar cells (PeSCs) requires effective passivation materials. In our study, we investigated the impact of varying concentrations of cesium iodide (CsI), an alkali halide, on the interface layer among the hole transporting layer (HTL) and the perovskite film in a triple-cation lead hybrid halide Cs0.15FA0.81MA0.04Pb(I2.86Br0.14)3 perovskite layer. Our findings revealed that the introduction of CsI into the NiOx HTL led to improved crystallinity and a reduction in defects within the perovskite film. Consequently, the photovoltaic performance of the CsI-modified PeSC exhibited a notable enhancement. Specifically, the photoelectric conversion efficiency (PCE) increased from 18.7 % in the original PeSC, which lacked CsI modification, to 20.5 %. Moreover, this improvement in PCE was accompanied by excellent stability, with the CsI-modified PeSC retaining 80 % of its opening PCE even afterward 144 h of testing.

Scalable and cost-effective fabrication of high-performance self-powered heterojunction UV-photodetectors using slot-die printing of triple-cation lead perovskite coupled with triboelectric nanogenerators

The demand for continuous monitoring of ultraviolet (UV) radiation, which poses significant health risks, has grown significantly with the advent of the internet of things (IoT) for human health. The need for a self-powered system that does not rely on battery charging in environmental conditions has led to the exploration of triboelectric nanogenerators (TENGs) as a promising energy source for sensor systems. In this study, we present a fully printed UV photodetector (UV-PD) that is fabricated through scalable slot-die printing of either single-layer triple-cation mixed halide perovskite (TCMHP) or a heterojunction of TiO2/TCMHP on patterned fluorine-doped tin oxide (FTO). The integrated TENG generates the required energy from the tapping of Kapton to the FTO contact, making the device self-powered. Our self-powered PD exhibits an excellent responsivity and detectivity of 71.4 mA W−1 and 6.92 × 1010 Jones, respectively, under a 395 nm wavelength, significantly outperforming spin-coated TCMHP-based devices. We further optimized the performance of our integrated TENG-powered heterojunction TiO2/TCMHP UV-PD by fabricating sensors with groove spacings of 2, 3, 5, and 8 mm. The optimized device demonstrated an unprecedented responsivity, detectivity, and EQE% of 151.9 mA W−1, 1.29 × 1011 Jones, and 47.8%, respectively, under UV irradiation. Our work represents a significant step towards large-scale industrial flexible self-powered UV detection devices that can protect human health and safety. This study highlights the potential of scalable and cost-effective slot-die printing techniques for the industrial production of high-performance self-powered UV sensors, with significant implications for IoT-based health monitoring and environmental protection applications.

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Efficiency Approaching 26% in Triple Cation Mixed Halide Perovskite Solar Cells by Numerical Simulation

Triple cation mixed halide perovskite solar cells have exhibited a great deal of interest and could be the potential candidate with an enhanced power conversion efficiency (PCE) as compared to conventional perovskite solar cells. In this article, we have simulated the various photovoltaic characteristics of [Cs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.05</sub> (MA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.17</sub> FA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.83</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.95</sub> Pb(I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.83</sub> Br <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.17</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ] based mixed cation mixed halide perovskite solar cells in n-i-p configurations. We have demonstrated and substantiated the experimentally reported device performances in identical device configurations using the same materials. The effect of variation in different hole transport layers, electron transport layers, doping density, and the thickness of various layers on device performance is thoroughly analyzed through our simulation. Further optimization of device performance is carried out by changing the thickness, doping concentration, and defect density of the active layer, and the PCE of 25.95% is achieved.

Effect of bromide doping on the phase stability and shelf life of the triple cation mixed halide perovskite single-crystals

• Growth of triple cation mixed halide perovskite (TCMHP) single crystals. • Suppression of yellow phase in TCMHP single crystals by the addition of bromine. • Optimization of bromine content in TCMHP single crystal for long term stability. The spontaneous phase transition occurs in the Formamidinium lead iodide (FAPbI 3 ) perovskite from photoactive black α-FAPbI 3 to photo-inactive yellow δ- FAPbI 3 poses a severe challenge to the long-term stability of this otherwise highly attractive photoactive material. The low-energy rotation of the formamidinium (FA) cation is expected to cause the phase instability of black α-FAPbI 3 phase perovskite. When bromine is incorporated into the perovskite octahedron, the fraction of actively rotating FA molecules get reduced, resulting in the black phase stabilization. In this context, it has been reported here a method to grow single crystals of FA 0.9 MA 0.05 Cs 0.05 PbI 3-x Br x (x = 0, 0.3, 0.6 and 0.9) without yellow δ- FAPbI 3 phase formation using bromine doping into the precursor solution. Further research into the effect of bromine content on the long-term stability of grown single crystals revealed that keeping the bromine content at 10 M percentage can extend the lifetime of the multi-cation perovskite single crystals over a month.

Polarization suppresses local photocurrent in triple-cation mixed-halide perovskite

Triple-cation mixed-halide perovskite Cs0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 (CsFAMA) has emerged as one of the most promising candidates for future high-efficiency solar cells. Ferroelectricity has been recognized as a critical issue in perovskite photovoltaics, although its existence and influence on photovoltaic performance remain controversial. We verify the ferroelectric polarization and reveal that it can suppress local photocurrent in CsFAMA through photoconductive atomic force microscopy (pc-AFM) and piezoresponse force microscopy (PFM). The time evolution of pc-AFM and PFM mappings first demonstrates that the photocurrents decreased with increasing electromechanical responses. Systematic characterization based on the first and second harmonic pointwise measurement as well as mappings shows that piezoelectricity primarily contributes to the measured electromechanical responses, while the ionic activity takes a back seat. Clear hysteresis loops and relaxation behaviors further confirm that the piezoresponse originates from ferroelectric polarization. Finally, based on temperature-dependent studies, we conclude that it is the ferroelectric polarization that weakens local photocurrent. This work provides insights into optimizing the photovoltaic performance of triple-cation mixed-halide perovskite solar cells.

Planar heterojunction perovskite solar cell with graded energy band architecture via fast-drying spray deposition

The fast-drying spray deposition (FDSD) technique for perovskite solar cells (PSCs) is developed to enable the stacking of perovskite absorbers with different work functions, which allows the creation of an additional built-in electric field at the interface during the fermi level realignment process upon contact. FDSD is functional under high relative humidity (RH) ambiance and by design, deposits dry film without the need for post-deposition annealing treatment. Based on a spray coating process, FDSD is also highly scalable. Leveraging FDSD’s multilayer deposition capability, this work explores the implementation of graded energy band architectures to achieve PSCs with enhanced carrier extraction and photovoltaic performances. To demonstrate the potential benefit of this approach, two triple cation mixed halide perovskite formulas are chosen. The two formulas, when stacked together in correct order, produce a heterojunction PSC device with an extra built-in electric field, which helps drift charge carriers towards desired electrodes. The architecture with the proper energy band alignment therefore exhibits enhanced carrier extraction efficiency and, despite being subjected to over 60–80% RH during fabrication, reaches the mean power conversion efficiency (PCE) of 7.4%, with the maximum value of 9.5%. The average PCE translates to over 9.9% and 10.3% improvements over the devices based on the two constituent formulas individually. FDSD demonstrates great flexibility i.e., in-humid-air fabrication process and requiring no post annealing treatments, thereby enabling extremely robust and scalable stacked architecture PSCs with low cost and good performance.

Exploring Nanoscale Structure in Perovskite Precursor Solutions Using Neutron and Light Scattering

Tailoring the solution chemistry of metal halide perovskites requires a detailed understanding of precursor aggregation and coordination. In this work, we use various scattering techniques, including dynamic light scattering (DLS), small angle neutron scattering (SANS), and spin–echo SANS (SESANS) to probe the nanostructures from 1 nm to 10 μm within two different lead-halide perovskite solution inks (MAPbI3 and a triple-cation mixed-halide perovskite). We find that DLS can misrepresent the size distribution of the colloidal dispersion and use SANS/SESANS to confirm that these perovskite solutions are mostly comprised of 1–2 nm-sized particles. We further conclude that if there are larger colloids present, their concentration must be <0.005% of the total dispersion volume. With SANS, we apply a simple fitting model for two component microemulsions (Teubner–Strey), demonstrating this as a potential method to investigate the structure, chemical composition, and colloidal stability of perovskite solutions, and we here show that MAPbI3 solutions age more drastically than triple cation solutions.

Moisture‐Induced Non‐Equilibrium Phase Segregation in Triple Cation Mixed Halide Perovskite Monitored by In Situ Characterization Techniques and Solid‐State NMR

Environmental stability is a major bottleneck of perovskite solar cells. Only a handful of studies are investigating the effect of moisture on the structural degradation of the absorber. They mostly rely on ex situ experiments and on completely degraded samples, which restrict the assessment on initial and final stage. By combining in situ X‐ray diffraction under controlled 85% relative humidity, and live observations of the water‐induced degradation using liquid‐cell transmission electron microscopy, we reveal two competitive degradation paths leading on one hand to the decomposition of state‐of‐the‐art mixed cation/anion (Cs0.05(MA0.17FA0.83)0.95Pb(Br0.17I0.83)3 (CsMAFA) into PbI2 through a dissolution/recrystallization mechanism and, on the other hand, to a non‐equilibrium phase segregation leading to CsPb2Br5 and a Cesium‐poor/iodide‐rich Cs0.05‐x(MA0.17FA0.83)0.95Pb(Br0.17−2yI0.83+2y)3 perovskite. This degradation mechanism is corroborated at atomic‐scale resolution through solid‐state 1H and 133Cs NMR analysis. Exposure to moisture leads to a film containing important heterogeneities in terms of morphology, photoluminescence intensities, and lifetimes. Our results provide new insights and consensus that complex perovskite compositions, though very performant as champion devices, are comparatively metastable, a trait that limits the chances to achieve long‐term stability.

In-Depth Chemical and Optoelectronic Analysis of Triple-Cation Perovskite Thin Films by Combining XPS Profiling and PL Imaging.

The investigation of chemical and optoelectronic properties of halide perovskite layers and associated interfaces is crucial to harness the full potential of perovskite solar cells. Depth-profiling photoemission spectroscopy is a primary tool to study the chemical properties of halide perovskite layers at different scales from the surface to the bulk. The technique employs ionic argon beam thinning that provides accurate layer thicknesses. However, there is an urgent need to corroborate the reliability of data on chemical properties of halide perovskite thin films to better assess their stability. The present study addresses the question of the Ar+ sputtering thinning on the surface chemical composition and the optoelectronic properties of the triple-cation mixed-halide perovskite by combining X-ray photoemission spectroscopy (XPS) and photoluminescence (PL) spectroscopy. First, XPS profiling is performed by Ar+ beam sputtering on a half-cell: glass/FTO/c-TiO2/perovskite. The resulting profiles show a very homogeneous and reproducible element distribution until near the buried interface; therefore, the layer is considered as quasihomogeneous all over its thickness, and the sputtering process is stable. Second, we evaluated a set of thinned perovskite layers representative of selected steps along the profile by means of PL imaging optical measurements in both steady-state and transient regimes to assess possible perturbation of the optical properties from the surface to bulk. Obtained PL spectra inside the resulting craters show no peak shift nor phase segregation. Accordingly, the transient PL measurements do not reveal any changes of the surface recombination rate in the sputtered areas. This demonstrates that there is no cumulative effect of sputtering nor drastic chemical and optoelectronic modifications, validating the determination of the in-depth composition of the perovskite layer. Combining XPS profiling with PL characterization can be a precise tool to be applied for an extensive study of the multiple layers and mixed organic/inorganic interfaces of photovoltaic devices.

Effects of temperature-dependent burn-in decay on the performance of triple cation mixed halide perovskite solar cells

The understanding of the degradation mechanisms in perovskite solar cells (PSCs) is important as they tend to degrade faster under exposure to heat and light conditions. This paper examines the temperature-dependent degradation of solution processed triple-cation mixed halide PSCs (Cs0.05(FA0.95MA0.05)0.95Pb(I0.9Br0.05)3). The PSCs were subjected to temperatures between 30 and 60 °C for 3 h (180 min) to evaluate their current–voltage performance characteristics. Temperature-induced changes in the layer and interfacial structure were also elucidated by scanning electron microscopy (SEM). Our results show that thermally induced degradation leads gradually to the burn-in decay of photocurrent density, which results in a rapid reduction in power conversion efficiency. The SEM images reveal thermally induced delamination and microvoid formation between the layers. The underlying degradation in the solar cell performance characteristics is associated with the formation of these defects (interfacial cracks and microvoids) during the controlled heating of the mixed halide perovskite cells. The electrochemical impedance spectroscopy analysis of the PSCs suggests that the device charge transport resistance and the interfacial capacitance associated with charge accumulation at the interfaces both increase with extended exposure to light.

Real-Time TEM Imaging of Moisture-Induced Degradation of Triple Cation Mixed Halide Perovskite

Real-Time TEM Imaging of Moisture-Induced Degradation of Triple Cation Mixed Halide Perovskite

Interfacial Defects Change the Correlation between Photoluminescence, Ideality Factor, and Open-Circuit Voltage in Perovskite Solar Cells.

The ideality factor (nid ) and photoluminescence (PL) analyses assess charge recombination characteristics in perovskite solar cells (PeSCs). However, their correlations with open-circuit voltage (Voc ) are often found to be complicated depending on the recombination types in the devices. Herein, the correlation of nid , PL characteristics and Voc is elucidated depending on the interfacial crystal quality in triple-cation mixed-halide perovskite, Cs0.05 (MA0.17 FA0.83 )0.95 Pb(I0.83 Br0.17 )3 , deposited on different hole transport layers (HTLs). In the devices with low quality interfacial crystals, Voc increases together with nid , which originates from the light intensity-dependence of majority carrier at the interface. Meanwhile, a negative correlation between Voc and nid is observed for devices with high quality interfacial crystals. The authors discuss the cases that PL enhancement by the improvement of overall crystal quality can fail to correlate with a Voc increase if interfacial crystal quality becomes worse. The study highlights that interfacial crystal quality evaluation can help to understand charge recombination via nid and PL measurements, and more importantly provide information of which defect engineering between at the interface and in the bulk would be more effective for device optimization.

Influence of spin-coating methods on the properties of planar solar cells based on ambient-air-processed triple-cation mixed-halide perovskites

Highly efficient perovskite solar cells based on triple-cation mixed-halide perovskite (CsFAMAPbIBr) require a strictly controlled environment such as a N2-filled glove box and/or a dry room due to the instability of formamidinium (FA) ions in humid environment. Furthermore, sufficient knowledge regarding the detailed ambient air processing techniques is lacking. Therefore, the processing of efficient CsFAMAPbIBr-based solar cells in ambient air atmosphere is very challenging and essential for low-cost commercialization. Herein, the effect of different coating methods, static spin coating and dynamic spin coating, on the fabrication of two-step ambient-air-processed CsFAMAPbIBr films and the photovoltaic properties of CsFAMAPbIBr-based planar solar cells is presented. Different compositions and morphologies of CsFAMAPbIBr are obtained because of the different reaction times between the pre-deposited PbI2-CsI layer and the secondary deposited organic materials (FAI/MABr/MACl) in static and dynamic spin-coating methods, which lead to differences in Ostwald ripening and ion exchange in ambient-air atmosphere, thereby substantially affecting the power conversion efficiency (PCE) and stability of the fabricated solar cells. Planar solar cells based on dynamic-spin-coated CsFAMAPbIBr exhibit a higher PCE of 19.70% (17.27% ± 1.25%), than those based on static-spin-coated CsFAMAPbIBr, whose PCE was 16.01% (9.89% ± 2.34%).

Unraveling the varied nature and roles of defects in hybrid halide perovskites with time-resolved photoemission electron microscopy.

With rapidly growing photoconversion efficiencies, hybrid perovskite solar cells have emerged as promising contenders for next generation, low-cost photovoltaic technologies. Yet, the presence of nanoscale defect clusters, that form during the fabrication process, remains critical to overall device operation, including efficiency and long-term stability. To successfully deploy hybrid perovskites, we must understand the nature of the different types of defects, assess their potentially varied roles in device performance, and understand how they respond to passivation strategies. Here, by correlating photoemission and synchrotron-based scanning probe X-ray microscopies, we unveil three different types of defect clusters in state-of-the-art triple cation mixed halide perovskite thin films. Incorporating ultrafast time-resolution into our photoemission measurements, we show that defect clusters originating at grain boundaries are the most detrimental for photocarrier trapping, while lead iodide defect clusters are relatively benign. Hexagonal polytype defect clusters are only mildly detrimental individually, but can have a significant impact overall if abundant in occurrence. We also show that passivating defects with oxygen in the presence of light, a previously used approach to improve efficiency, has a varied impact on the different types of defects. Even with just mild oxygen treatment, the grain boundary defects are completely healed, while the lead iodide defects begin to show signs of chemical alteration. Our findings highlight the need for multi-pronged strategies tailored to selectively address the detrimental impact of the different defect types in hybrid perovskite solar cells.

Potassium-containing triple-cation mixed-halide perovskite materials: Toward efficient and stable solar cells

In this paper, potassium based triple cation mixed-halide perovskite films were explored in order to enhance the stability and photovoltaic performance of perovskite based solar cells. It was found that adding potassium (K+) to a double cation mixed halide perovskite (FA0.80MA0.20PbI2.8Cl0.2), structural, morphological and optoelectronic properties of perovskites are improved. The perovskite films were prepared by one-step spin coating method with and without K+ and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). The results indicate that potassium incorporation reduces significantly the yellow non-perovskite δ-phase formation and improves the perovskite film quality, thus contributing to the reduction of hysteresis, improves the stability and increases the PCE up to 12.51%. Furthermore, the doped devices exhibit reduced hysteresis and provide remarkable shelf stability by retaining more than 70% of the initial efficiency with low humidity over 850 h.

Minimizing the Trade-Off between Photocurrent and Photovoltage in Triple-Cation Mixed-Halide Perovskite Solar Cells

Its lower bandgap makes formamidinium lead iodide (FAPbI3) a more suitable candidate for single-junction solar cells than pure methylammonium lead iodide (MAPbI3). However, its structural and thermodynamic stability is improved by introducing a significant amount of MA and bromide, both of which increase the bandgap and amplify trade-off between the photocurrent and photovoltage. Here, we simultaneously stabilized FAPbI3 into a cubic lattice and minimized the formation of photoinactive phases such as hexagonal FAPbI3 and PbI2 by introducing 5% MAPbBr3, as revealed by synchrotron X-ray scattering. We were able to stabilize the composition (FA0.95MA0.05Cs0.05)Pb(I0.95Br0.05)3, which exhibits a minimal trade-off between the photocurrent and photovoltage. This material shows low energetic disorder and improved charge-carrier dynamics as revealed by photothermal deflection spectroscopy (PDS) and transient absorption spectroscopy (TAS), respectively. This allowed the fabrication of operationally stable perovskite solar cells yielding reproducible efficiencies approaching 22%.

Cd-Doped Triple-Cation Perovskite Thin Films with a 20 μs Carrier Lifetime

Triple-cation mixed-halide perovskite of composition Csx(FAyMA1–y)1–xPb(IzBr1–z)3 (denoted as FAMACs) is a promising optoelectronic material due to many attractive optoelectronic properties. Reducing the defect density in FAMACs polycrystalline thin films is critical for the improvement of their photovoltaic performance. Herein, we report that by incorporating CdCl2 into FA0.9MA0.05Cs0.05PbI2.7Br0.3 polycrystalline films, the bulk carrier lifetime is prolonged to ∼20 μs, similar to that in single crystals, and the intrinsic surface defect density is reduced to as low as (6.72 ± 0.01) × 1013 cm–3. The incorporation of CdCl2 leads to an increase of power conversion efficiency (PCE) of FAMACs solar cell from 20.4% to 22.1%, which is attributed to a larger Voc due to the removal of bulk defects by Cd ions doping and Cl-ion-assisted crystallization. However, further improvement of PCE is likely limited by the interface defects produced during the deposition of the charge transport layer in constructing solar cells.

Grain Boundary Defect Passivation of Triple Cation Mixed Halide Perovskite with Hydrazine-Based Aromatic Iodide for Efficiency Improvement

Perovskites have been unprecedented with relatively sharp rise in power conversion efficiency in the last decade. However, the polycrystalline nature of the perovskite film makes it susceptible to surface and grain boundary defects, which significantly impedes its potential performance. Passivation of these defects has been an effective approach to further improve photovoltaic performance of the perovskite solar cells. Here, we report use of a novel hydrazine-based aromatic iodide salt or phenyl hydrazinium iodide (PHI) for secondary post treatment to passivate surface and grain boundary defects in triple cation mixed halide perovskite films. In particular, the PHI post-treatment reduced current at the grain boundaries, facilitated an electron barrier and reduced trap state density, indicating suppression of leakage pathways and charge recombination, thus passivating the grain boundaries. As a result, a significant enhancement in power conversion efficiency to 20.6% was obtained for the PHI-treated perovskite device in comparison to control device with 17.4%.