Mixed-cation Perovskite Research Articles

Insight into Charge Carrier Recombination Mechanisms in Lead Based Mixed Cation and Halide Perovskite

Insight into Charge Carrier Recombination Mechanisms in Lead Based Mixed Cation and Halide Perovskite

Synergistic strategy of rubidium chloride regulated SnO2 and 4-tert-butyl-benzylammonium iodide passivated MAxFA1-xPbI3 for efficient mixed-cation perovskite solar cells

Nowadays, the MA-FA mixed-cation perovskite solar cells (PSCs), demonstrating much higher stability than that of single-cation MAPbI3 or FAPbI3, are still encountering a low-efficiency issue. The main reason is that there existing a lot of defects in SnO2 electron transport layers (ETLs) and perovskite absorbers. Herein, we develop a synergistic strategy of Rubidium Chloride (RbCl) doping and 4-tert-butylbenzylammonium iodide (tBBAI) passivation to fabricate high-performance MAxFA1-xPbI3 mixed-cation PSCs. The alkali halide RbCl is first selected as a novel doping additive to regulate the film properties of SnO2 and perovskites. Research shows that the negative Cl- ions can combine with uncoordinated Sn4+ ions due to their strong bonding ability, which can passivate the oxygen-vacancy-related defects and enhance the charge transport of SnO2 ETLs. Meanwhile, the doped Rb+ and Cl- ions may diffuse into perovskite lattices to promote grain growth and reduce the defects of perovskites. Besides, we employ an organic halide salt tBBAI to passivate perovskites and suppress surface defects. Results of deep level transient spectroscopy (DLTS) indicate that SnO2 and SnO2-RbCl based devices have deeper hole traps and large trap densities (ΔE = 0.92 eV, NT = 1.10 × 1016 cm−3; ΔE = 0.93 eV, NT = 2.16 × 1015 cm−3); while tBBAI-treated SnO2-RbCl-based devices own a shallower hole trap and a smaller trap density (ΔE = 0.72 eV, NT = 2.44 × 1013 cm−3); and the corresponding IPb and I(MA/FA) antisite defeats are also identified. Therefore, our synergistic strategy is effectively able to reduce the defect density and suppress the non-radiative recombination. Consequently, the best-performance MA0.85FA0.15PbI3 PSCs achieve an impressive power conversion efficiency (PCE) of 22.54% with a large open circuit voltage (Voc) of 1.16 V, which are by far the highest values of MA0.85FA0.15PbI3 mixed-cation PSCs.

Ion Migration as a New Paradigm to Boost Self‐Driven Perovskite Narrowband Photodetectors

AbstractHalide perovskite narrowband photodetectors based on a charge collection narrowing mechanism have emerged as a new class of optoelectronic devices for monochromatic imaging. However, improving the figures‐of‐merit of such narrowband photodetectors remains challenging due to the inability to manipulate the major material players in the elusive photoresponse process. Here, a novel approach of manipulating ion migration to enhance the narrowband photoresponse of self‐driven p‐i‐n type photodetectors is taken by intentionally adding mobile ions into the formamidine and methylamine mixed cation perovskite layer. The excess mobile ions reduce the activation energy of ion migration, and this facilitated migration orchestrates the ions in the perovskite layer to re‐engineer the energy band, and thus modulates the charge separation and collection energetics and kinetics, leading to an unprecedented boost of the narrowband photoresponse. The photodetector based on this approach achieved a peak responsivity of as high as 112.41 mA W−1 at 820 nm at zero bias with a full‐width at half maximum of only 22 nm and an over 3‐fold improvement in the spectral rejection ratio, making it highly promising for the next‐generation color imaging devices.

Mixed-Cation Halide Perovskite Doped with Rb+ for Highly Efficient Photodetector.

Photodetectors are widely employed as fundamental devices in optical communication, automatic control, image sensors, night vision, missile guidance, and many other industrial or military fields. Mixed-cation perovskites have emerged as promising optoelectronic materials for application in photodetectors due to their superior compositional flexibility and photovoltaic performance. However, their application involves obstacles such as phase segregation and poor-quality crystallization, which introduce defects in perovskite films and adversely affect devices' optoelectronic performance. The application prospects of mixed-cation perovskite technology are significantly constrained by these challenges. Therefore, it is necessary to investigate strategies that combine crystallinity control and defect passivation to obtain high-quality thin films. In this study, we incorporated different Rb+ ratios in triple-cation (CsMAFA) perovskite precursor solutions and studied their effects on crystal growth. Our results show that a small amount of Rb+ was enough to induce the crystallization of the α-FAPbI3 phase and suppress the formation of the yellow non-photoactive phase; the grain size increased, and the product of the carrier mobility and the lifetime (μτ) improved. As a result, the fabricated photodetector exhibited a broad photo-response region, from ultraviolet to near-infrared, with maximum responsivity (R) up to 11.8 mA W-1 and excellent detectivity (D*) values up to 5.33 × 1011 Jones. This work provides a feasible strategy to improve photodetectors' performance via additive engineering.

Increasing the Performance and Stability of Red-Light-Emitting Diodes Using Guanidinium Mixed-Cation Perovskite Nanocrystals.

Halide perovskite nanocrystals (PNCs) exhibit growing attention in optoelectronics due to their fascinating color purity and improved intrinsic properties. However, structural defects emerging in PNCs progressively hinder the radiative recombination and carrier transfer dynamics, limiting the performance of light-emitting devices. In this work, we explored the introduction of guanidinium (GA+) during the synthesis of high-quality Cs1-xGAxPbI3 PNCs as a promising approach for the fabrication of efficient bright-red light-emitting diodes (R-LEDs). The substitution of Cs by 10 mol % GA allows the preparation of mixed-cation PNCs with PLQY up to 100% and long-term stability for 180 days, stored under air atmosphere and refrigerated condition (4 °C). Here, GA+ cations fill/replace Cs+ positions into the PNCs, compensating intrinsic defect sites and suppressing the nonradiative recombination pathway. LEDs fabricated with this optimum material show an external quantum efficiency (EQE) near to 19%, at an operational voltage of 5 V (50-100 cd/m2) and an operational half-time (t50) increased 67% respect CsPbI3 R-LEDs. Our findings show the possibility to compensate the deficiency through A-site cation addition during the material synthesis, obtaining less defective PNCs for efficient and stable optoelectronic devices.

Interface engineering of Tin(IV) oxide electron transport layer with Yttrium(III) fluoride for efficient carbon-based perovskite solar cells

Carbon-based perovskite solar cells (C–PSCs) are the most promising technology to meet global energy demands at a reasonable price. In the current study, to assemble efficient and stable C–PSCs, the interface between the tin oxide electron transport layer and the mixed-cation perovskite layer was tailored by coating yttrium fluoride (YF3) material over the tin oxide layer. Results show that YF3–SnO2 ETL produces a more suitable substrate for perovskite fabrication, causing the formation of a perovskite layer with enlarged grains and a lower PbI2 residual. In addition, the results indicate that YF3 treatment could boost the conductivity of SnO2, reduce defects in the mixed-cation perovskite layer, and suppress nonradiative recombination in the C–PSCs. YF3-based interface engineering brought champion C–PSCs with an efficiency of 14.01% under simulated illumination of 100 mW cm−2, which was considerably higher than the 11.58% recorded for control C–PSCs. After 168 days of aging, the unsealed, modified C-PSC devices can demonstrate superior ambient air stability behavior conditions and retain 95% of their initial performance.

IPL-Annealed Mixed-Cation Perovskites with Robust Coating Window toward Scalable Manufacturing of Commercial Perovskite Solar Cells

Perovskite solar cells (PSCs) are a promising alternative solar technology, but the technical challenges of (1) stability/durability, (2) efficiency at scale, and (3) manufacturability must be overcome to achieve widespread PSC commercialization. The challenge of balancing solution ink formulation and scalable manufacturing is often overlooked in the literature, where focus is on adopting inks from processes that will not scale. In this study, we apply a classical roll-to-roll manufacturing perspective, utilizing both compositional engineering and intense pulsed light (IPL) annealing, to develop a mixed-cation perovskite ink with a robust coating window that simultaneously solve issues of stability and manufacturability for PSCs. Our method resulted in blade-coated, flexible, mixed-cation PSCs on ITO-PET substrates with a champion power conversion efficiency (PCE) efficiency of 16.7% using IPL annealing of the absorber layer and, to our knowledge, is one of the fastest processing methods for the perovskite layer. This overall reduction in processing time with a stable ink represents an advance toward the scaled production of perovskite solar cells on flexible substrates.

Myth behind Metastable and Stable n-Hexylammonium Bromide-Based Low-Dimensional Perovskites

In perovskite solar cells, passivating the surface or interface that contains a high concentration of defects, specifically deep-level defects, is one of the most important topics to substantially enhance the power conversion efficiency and stability of the devices. Long-chain alkylammonium bromides have been widely and commonly adapted for passivation treatment. However, the mechanism behind is still not well explored as the formation route and the exact structure of these alkylammonium bromide-based low-dimensional perovskites are unclear. Herein, we investigate the physical and chemical properties of an n-hexylammonium bromide (HABr)-based low-dimensional perovskite including both thin films and single crystals. First of all, the HA2PbBr4 perovskite film and aged single crystal demonstrate different X-ray diffraction patterns from those of the fresh as-prepared single crystal. We found that the fresh HA2PbBr4 single crystal exhibits a metastable phase as its structure changes with aging due to the relaxation of crystal lattice strains, whereas the HA2PbBr4 perovskite film is pretty stable as the aged single crystal. Upon reacting with FAPbI3, HABr can be intercalated into the FAPbI3 lattice to form a mixed-cation perovskite of HAFAPbI3Br, which is in a dynamic equilibrium of decomposition and formation. In contrast, the reaction of HABr with excess PbI2 forms a stable HA2PbI2Br2 perovskite. Based on such findings, we rationally develop a HA2PbI2Br2-passivated FACs-based perovskite by reacting HABr with excess PbI2, the photovoltaics based on which are more stable and efficient than those passivated by the HAFAPbI3Br perovskite. Our discovery paves way for a more in-depth study of bromide-containing low-dimensional perovskites and their optoelectronic applications.

Synergistic Effect of Cation Composition Engineering of Hybrid Cs1−xFAxPbBr3 Nanocrystals for Self‐Healing Electronics Application (Adv. Mater. 9/2023)

Self-Healing Nanophotonics In article number 2207617, Fang-Cheng Liang, Takayuki Chiba, Junji Kido, Chi-Ching Kuo, and co-workers present novel post-synthesis Cs/FA mixed-cation perovskite nanocrystals possessing high structural and optoelectronic properties for integration in self-healing polymer composites. The entropy-driven self-healing not only enhances the white backlight display performance but also sustains the shattered–repaired glass substrate laser working performance, thereby representing potentially major advances in optoelectronics and photonics applications.

Development for Highly Efficient Organometal Halide Perovskite Solar Cells and Modules

Organometal halide perovskites have captured wide interest as a promising material for light-weight and high-efficiency solar cells. Through recent studies of the organometal halide perovskite solar cells (PSCs), the composition of organometal halide perovskites is recognized as one of the key factors in the improvement of the PCE. In this study, we investigated mixed cation perovskite absorber. Additionally, we successfully constructed monolithic PSC mini-module without I-V hysteresis. In the case of MA-free PSCs, the 24.9% PCE (0.187 cm2) and 21.6% PCE (2.76 cm2 monolithic PSC mini-module) were obtained, respectively. We also developed semitransparent perovskite top cells with higher durability and transmittance for tandem solar cells. The PCEs of 19.5% (certified 19.3%) and 26.2% were achieved for a 1 cm2 semi-transparent perovskite top cell and four-terminal PSC/CIGS tandem solar cells, respectively.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Radical polymeric p-doping and grain modulation for stable, efficient perovskite solar modules.

High-quality perovskite light harvesters and robust organic hole extraction layers are essential for achieving high-performing perovskite solar cells (PSCs). We introduce a phosphonic acid-functionalized fullerene derivative in mixed-cation perovskites as a grain boundary modulator to consolidate the crystal structure, which enhances the tolerance of the film against illumination, heat, and moisture. We also developed a redox-active radical polymer, poly(oxoammonium salt), that can effectively p-dope the hole-transporting material by hole injection and that also mitigates lithium ion diffusion. Power conversion efficiencies of 23.5% for 1-square-centimeter mixed-cation-anion PSCs and 21.4% for 17.1-square-centimeter minimodules were achieved. The PSCs retained 95.5% of their initial efficiencies after 3265 hours at maximum power point tracking under continuous 1-sun illumination at 70° ± 5°C.

Understanding Auger recombination in perovskite solar cells.

Enhanced radiative efficiency, long carrier lifetimes, and high carrier mobilities are hallmarks of perovskite solar cells. Considering this, complete cells experience large nonradiative recombination losses that restrict their VOC considerably below the Shockley-Queisser limit. Auger recombination, which involves two free photo-induced carriers and a trapped charge carrier, is one potential mechanism. Herein, the effects of Auger capture coefficients in mixed-cation perovskites are analyzed employing SCAPS-1D computations. It is demonstrated that VOC and FF are severely decreased with an increase in the acceptor concentration and Auger capture coefficients of perovskites, thus reducing the device performance. When the Auger capture coefficient is increased to 10-20 cm6 s-1 under the acceptor concentration of 1016 cm-3, the performance is drastically lowered from 21.5% (without taking Auger recombination into account) to 9.9%. The findings suggest that in order to increase the efficiency of perovskite solar cells and prevent the effects of Auger recombination, the Auger recombination coefficients should be less than 10-24 cm6 s-1.

Air-stable mixed cation lead halide perovskite films and microscopic study of their degradation process.

We report the preparation and nanoscale photophysical characterization of mixed cation perovskite films of the composition MA1-xFAxPbI3, with x = 0, 0.3 and 0.5. Films with x = 0.5 and 0.3 prepared in air using ethyl acetate as an antisolvent in a one-step spin-coating process are compositionally stable in ambient air for more than a year, in contrast to films prepared using a chlorobenzene antisolvent. The onset of degradation of the films near the film edges was monitored using in situ photoluminescence (PL) spectroscopy. The PL spectra of the degradation products are consistent with the PL spectra of 2D perovskite sheets of varying thicknesses. Morphologically, aging of the films brings about coalescing of the film grain structure into larger crystal grains. Furthermore, monitoring of the time traces of PL from individual nanoscale locations in the films (PL blinking) reveals that aging of the films does not change the extent of dynamic PL quenching or affect the observed long-range charge diffusion on the order of micrometers.

Metal Halide Perovskite Surfaces with Mixed A‐Site Cations: Atomic Structure and Device Stability

AbstractMixing cations in the perovskite structure has been shown to improve optoelectronic device performance and stability. In particular, CsxMA1‐xPbBr3 (MA = CH3NH3) has been used to build high‐efficiency light‐emitting diodes. Despite those advantages, little is known about the exact location of the cations in the mixed perovskite film, and how cation distribution affects device properties and stability. By using scanning tunneling microscopy , the exact atomic structure of the mixed cation CsxMA1‐xPbBr3 perovskite interface is revealed. In addition, X‐ray photoelectron spectroscopy, ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy are used to study the stability and electronic properties of the CsxMA1‐xPbBr3 perovskite film. Partial substitution of MA+ by Cs+ induces a modification of the perovskite surface structure, leading to improved device stability is shown. These results provide a better understanding of the key parameters involved in the stability of mixed cation perovskite solar cells.

Facile low-energy and open-air synthesis of mixed-cation perovskite quantum dots for high-performance solar cells

Cesium-formamidinium (FA) lead triiodide (Cs1−xFAxPbI3) perovskite quantum dots (PQDs) are promising building blocks for photovoltaics. However, the mixed-cation colloidal PQDs are difficult to be synthesized in one pot because of the differences in optimal reaction temperatures of Cs (180 °C) and FA (80 °C) precursors; therefore, they are obtained by cation-exchange reactions between pre-synthesized CsPbI3 and FAPbI3 PQDs. Herein, one-pot synthesis of Cs1−xFAxPbI3 PQDs is developed at 60 °C in open air, dramatically reducing the process time and energy consumption compared to the conventional cation-exchange method. Computational calculations considering temperature effects reveal that the formation of mixed-cation PQDs is thermodynamically favorable even at the low synthesis temperature. The temperature effects dominate the mixing energy over the configurational entropy effect as the temperature increased, and thus Cs crystallizes more easily than FA at the synthesis temperature. This one-pot synthesis also allows fine-tuning of the A-site cations of Cs1−xFAxPbI3 PQDs, enabling the control of crystal structures and optical properties, thus optimizing photovoltaic performance. As a result, the fabricated Cs1−xFAxPbI3 PQD solar cells exhibit power conversion efficiencies (PCEs) up to 11.58 %, which is the highest among the reported solar cells fabricated using QDs synthesized at ≤ 60 °C in open air. The optimized solar cell retains 92 % of its initial PCE value after 1,083 h in dry air (dark and relative humidity < 10 %).

Cation substitution-induced band gap and stability engineering of formamidinium-based perovskite films prepared in ambient conditions

An intermediate complex approach coupled with a preheating strategy are used to grow mixed-cation FA1-xCsxPbI3 perovskite films in ambient air. This was achieved through an effective PbI2 conversion and the elimination of the detrimental moisture effect, which was ensured by the formation of an intermediate complex along with the rapid solvent evaporation induced by the preheating of the substrate and/or precursor solutions. Moreover, it is found that the control of [CsI]/[FAI] ratio clearly influences the crystallization of the α-perovskite phase and could effectively inhibit the growth of non-perovskite crystallites, which stabilizes the photoactive α-phase. X-ray diffraction analyses indicate that a change in crystal orientation from (100) to (111) direction occurs for 35% CsI added in the perovskite precursor, inducing a decrease in the band gap energy. Moreover, the stability is significantly improved in the (111) direction, in agreement with computational results obtained in literature.

Elucidating degradation mechanisms of mixed cation formamidinium-based perovskite solar cells under device operation conditions

Organic cation-based metal halide perovskites suffer from volatile material decomposition, and the approach to ensure stability under device operation conditions is still far from commercialization. Formamidinium (FA)-based perovskite solar cells (PeSCs) have been widely used, showing efficient power conversion efficiencies (PCEs). Despite the high PCE, FA-based perovskites lack stability, but the related degradation mechanisms are quite indefinite. In this study, we compared two different systems by introduction of inorganic and organic cations to increase FA-based perovskite stability. To relate the device operational stability, we exposed the mixed cation perovskite films under 1 sun illumination at 60 °C in ambient air and investigated the difference in the phase transition of inorganic-mixed and organic-mixed FA perovskites. Morphological and structural characterizations were collected to confirm that the type of the secondary cation plays a major role in determining whether perovskite degradation is triggered at the grain boundary or perovskite grain surfaces. Although the PCEs of the two device systems are similar, the degradation mechanisms varied significantly depending on the chemical properties of perovskite components.

Achieving highly efficient and stable MAPbI3 planar solar cell by embedding Cs+, Fe2+, and Cd2+ metal inorganic cations in perovskite structure

Perovskite solar cells (PSCs) have been attracted the attention of many researchers due to their high conversion efficiency, low manufacturing cost, easy manufacturing steps, high light absorption, and the possibility of changing the photo electronic properties by modifying the chemical structure. Despite the mentioned advantages, the low stability of PSCs and toxicity of lead in the perovskite layer were the challenging issues in this field. In this regard, the use of mixed cation and mixed halide perovskite compounds with high crystal quality, efficiency, and stability has attracted enormous attention. In this project, Fe2+, Cd2+, and Cs+ cations with various contents (Fe2+ + Cd2+: 5% and 10%; Cs+: 5% and 10%) were partially replaced the Pb2+ and CH3NH3+ cations, respectively in the MAPbI3 perovskite structure through a two-step process using spin-coating. The as-synthesized [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 5, 10%, y: 5, 10%) perovskites were characterized with X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD), and field emission scanning electron microscopy (FESEM). The optical properties of prepared compounds were investigated by ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy. The photovoltaic behavior as well as stability of solar cells containing MAPbI3, [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 5%, y: 5%), and [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 10%, y: 10%) perovskites as active layers were evaluated by current density-voltage (I–V) under AM1.5G illumination.Results showed that partial substitution of CH3NH3+ cations with Cs+ and Pb2+ cations with Fe2+ + Cd2+ in the CH3NH3PbI3 structure improved crystallinity and photovoltaic parameters. The average power conversion efficiency (PCE) of six solar cell containing [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 10%, y: 10%) perovskite layer was 21.04% which was 1.03 and 1.21 times higher than that cells containing [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 5%, y: 5%) and MAPbI3, respectively.The electrochemical impedance spectroscopy (EIS) was utilized to study the charge transfer resistance (Rct) and recombination resistance (Rrec) of prepared solar cells. The Rct and Rrec values of fabricated solar cell were decreased and increased, respectively in the presence of Fe2+, Cd2+, and Cs+ inorganic cations. As a result, the [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a] perovskites can be considered as the appropriate candidate with high efficiency, stability, and low lead content in the planar perovskite solar cells.

Slot-die coating of a formamidinium-cesium mixed-cation perovskite for roll-to-roll fabrication of perovskite solar cells under ambient laboratory conditions

A deposition strategy is demonstrated for fabricating perovskite solar cells (PSCs) under ambient laboratory conditions. A nitrogen-flow treatment followed by a short (3 min), low-temperature (135 °C) anneal enables control of the nucleation and crystal growth of slot-die coated perovskite layers without the need for an anti-solvent for devices. PSCs using either glass or poly(ethylene terephthalate) (PET) substrates were prepared with an n-i-p device architecture and comprised a perovskite layer containing formamidinium and cesium cations, with or without the additive of 2-(2,3,4,5,6-pentafluorophenyl)-ethylammonium iodide (FEAI). The perovskite layer in glass-based devices was slot-die coated onto a stationary substrate with a moving coating head, whereas the deposition of the perovskite layer in PET-based devices was achieved by slot-die coating onto a moving (roll-to-roll, R2R) web using a stationary coating head. The processing conditions enabled the fabrication of PSCs displaying excellent temperature and humidity tolerance (up to 50% relative humidity). Devices fabricated on the glass substrates had power-conversion efficiencies (PCEs) of more than 18%, with PCEs of more than 15% measured for cells on the PET film substrates. The use of the FEAI additive improved the environmental stability of encapsulated glass-based PSC devices, which retained up to 70% of their initial PCE after 1000 h at maximum power point under 1-sun illumination in air. The scalability of the fabrication techniques used in this work, along with the low annealing temperature and ability to process in an ambient laboratory environment, makes this a promising approach for translation to industrial-scale R2R production processes.