Defects In Perovskites Research Articles

The synergistic effect of defect passivation and energy level adjustment for low-temperature carbon-based CsPbI2Br perovskite solar cells

Hydrophobic organic ammonium halide salts are used to passivate perovskite defects, adjust interfacial energy level alignments, and ultimately improve the efficiency and stability of low-temperature carbon-based CsPbI2Br perovskite solar cells.

Interfacial Modification via a 1,4-Butanediamine-Based 2D Capping Layer for Perovskite Solar Cells with Enhanced Stability and Efficiency.

Organic-inorganic perovskites face the issues of being vulnerable to oxygen and moisture and the trap sites located at the surface and grain boundaries. Integration of two-dimensional (2D) perovskites as a capping layer is an effective route to enhance both photovoltaic efficiency and environmental stability of the three-dimensional (3D) underlayer. Here, we employ 1,4-butanediammonium diiodide (BDADI), which has a short chain length and diammonium cations, to construct a 3D/2D stacking perovskite solar cells (PSCs). The introduction of BDA2+ could passivate surface defects in 3D perovskites by forming 2D Dion-Jacobson (DJ) phase perovskites and effectively suppressing nonradiative recombination, thus resulting in a longer carrier lifetime. The DJ 2D capping layer also regulate the energy level arrangement, enabling a better charge extraction and transport process. In addition, the water-resistance ability of 3D perovskite gets improved because of the hydrophobic characteristic of 1,4-butanediammonium cations. Consequently, the 3D/2D stacking PSCs yield an energy conversion efficiency of 20.32% in company with the enhanced long-term stability.

Mixing halogens improves the passivation effects of amine halide on perovskite

Defects passivation using organic halogenated amines as interlayer in perovskite solar cells attracts attentions in the few years. Herein, we focus on the barely studied halogen part of the organic halogenated amines layer, and systemically investigate the influence of halogen part on the perovskite defect passivation. Based on detailed comparison of the differences and advantages of IpAF, IpACl or IpABr as perovskite defect passivators, mixed-halogenated isopentylamines (IpAX, IpA = isopentylamine; X= F, Cl, Br mixture) are used as passivation layer on MAPbI3 surface to make full use of the advantages of each halogen. As expected, IpAX exhibits superiority as defect passivator over the any single-halogenated isopentylamine, and device based on IpAX achieves a best performance of 20.64% with greatly improved stability in 1000 h. These results highlight the importance of halogen part in organic halogenated amines on the passivation of defects for improvement of the efficiency and durability of solar cells.

Synergistic stabilization of CsPbI3 inorganic perovskite via 1D capping and secondary growth

Cesium lead iodide (CsPbI3) perovskite has gained great attention in the photovoltaic (PV) community because of its unique optoelectronic properties, good chemical stability and appropriate bandgap for sunlight harvesting applications. However, compared to solar cells fabricated from organic-inorganic hybrid perovskites, the commercialization of devices based on all-inorganic CsPbI3 perovskites still faces many challenges regarding PV performance and long-term stability. In this work, we discovered that tetrabutylammonium bromide (TBABr) post-treatment to CsPbI3 perovskite films could achieve synergistic stabilization with both TBA+ cation intercalation and Br-doping. Such TBA+ cation intercalation leads to one-dimensional capping with TBAPbI3 perovskite formed in situ, while the Br-induced crystal secondary growth helps effectively passivate the defects of CsPbI3 perovskite, thus enhancing the stability. In addition, the incorporation of TBABr can improve energy-level alignment and reduce interfacial charge recombination loss for better device performance. Finally, the highly stable TBABr-treated CsPbI3-based perovskite solar cells show reproducible photovoltaic performance with a champion efficiency up to 19.04%, while retaining 90% of the initial efficiency after 500 h storage without encapsulation.

Amino‐Linked Conjugated Tetrazole Ring Passivation Strategy for Air‐Processed Perovskite Cells with Predominant Stability and Efficiency

Perovskite solar cells (PSCs) develop rapidly with certified efficiency over 25.5 %, but there are remaining problems such as defects-induced recombination and degradation throughout the whole device. Functional organic small molecule passivation strategies are diverse and efficient, enhancing the efficiency and stability of PSCs. Here, 5-aminotetrazole (5ATZ) was introduced for the first time as an effective passivator, where -NH2 and -NH as active sites interacted with the Pb and I related to vacancy defects in perovskites, anchoring defects and preventing further unavoidable ion migration and device degradation. Furthermore, the extensive π-electron delocalization around the tetrazole conjugated ring significantly promoted the charge transfer. Therefore, the 5ATZ-processed PSCs provided enhanced voltage and current, showed superior 19.75 % power conversion efficiency with excellent performance and improved stability, and demonstrated one of the best performances in all-air preparation to date. The simultaneous multi-effect passivation strategy of vacancy defects in perovskites will contribute to eliminate obstacles on the road to commercialization of PSCs.

Investigation of lead-free MASnI3-MASnIBr2 tandem solar cell: Numerical simulation

Lead-free perovskite materials have attracted noteworthy interest for photovoltaics as they are free from toxicity and instability issues encountered in lead-based perovskites. In this work, we report on a simulation study of a two-terminal monolithic all lead-free tandem solar cell. The (MASnI3) cell with 1.3 eV bandgap is used as a bottom cell and the top cell is (MASnIBr2) with a bandgap of 1.75 eV. The calibration of the standalone bottom and top cells initially gives a conversion power efficiency (PCE) of 5.42% and 5.74%, respectively. After comprising these two initial sub-cells in a two-terminal all lead-free monolithic tandem cell, a tandem efficiency of 7.66% is obtained with a matching current is 10.36 mA/cm2 in this case. Based on parametric analysis, the values of perovskite doping, perovskite defect density and ETL/HTL affinity are optimized. The PCE of individual cells after enhancement has increased to 11.01% and 10.17% for bottom and top cells, respectively. As a result of the enhancement of the two cells, the tandem efficiency improves to 15.66% and the matching current also increases to 13.94 mA/cm2. In addition, the current matching point is tracked while changing the band gaps of bottom and top cells in the ranges of (1.1 eV–1.4 eV) and (1.55 eV–1.85 eV), and for the thicknesses in the ranges (150 nm–400 nm) and (150 nm–500 nm), respectively. The simulations done in this paper shows the significant influence of current matching point on the tandem cell performance. All simulations are performed by using SCAPS-1D under AM1.5G illumination.

Enhanced Activation Energy Released by Coordination of Bifunctional Lewis Base d-Tryptophan for Highly Efficient and Stable Perovskite Solar Cells.

Perovskite defect passivation with molecule doping shows great potential in boosting the efficiency and stability of perovskite solar cells (PSCs). Herein, an efficient and low-cost bifunctional Lewis base additive d-tryptophan is introduced to control the crystallization and growth of perovskite grains and passivation defects. It is found that the additive doped in the solution precursors could retard crystal growth by increasing activation energy, resulting in improved crystallization of large grains with reduced grain boundaries, as well as inhibiting ion migration and PbI2 aggregation. As a result, the PSCs incorporated with d-tryptophan additives achieve an improved power conversion efficiency from 18.18 to 21.55%. Moreover, the d-tryptophan passivation agent improves the device stability, which retains 86.85% of its initial efficiency under ambient conditions at room temperature after 500 h. This work provides Lewis base small-molecule d-tryptophan for efficient defect passivation of the grain boundaries toward efficient and stable PSCs.

Unraveling Passivation Mechanism of Imidazolium-Based Ionic Liquids on Inorganic Perovskite to Achieve Near-Record-Efficiency CsPbI2Br Solar Cells

HighlightsA series of 10 imidazolium-based ionic liquids (IILs) with different cations and anions have applied to unravel the passivation mechanism of the IILs on CsPbI2Br inorganic perovskites.It is found that anions of IILs play a more important role in passivation of lead- and cesium-related defects in inorganic perovskite compared with imidazole cations because they can form strong ionic interactions (Pb-F, Cs-F).A high-power conversion efficiency of 17.02% is obtained, which is among the highest values of CsPbI2Br-based perovskite solar cells.

Coordinating light management and advance metal nitride interlayer enables MAPbI3 solar cells with >21.8% efficiency

Due to the continuous increase in power conversion efficiencies (PCEs), perovskite solar cells (PSCs) are widely considered as the most promising technology for third generation photovoltaics. Improving optical absorption while reducing electrical losses is still a challenge towards attaining PCE values closer to the Shockley-Queisser limit. However, frequently used strategies to improve light absorption (e.g. via texturing the front surface) often cause electrical recombination losses. Here, we successfully relaxed the competing mechanisms between electrical and optical properties by integrating a modulated textured substrate and an amorphous metal nitride interface modification layer to combine enhanced light scattering and reducing interfacial recombination losses in PSCs. This comprehensive electro-optical management presents several advantages, including increased light absorption, promoting bandgap alignment and passivating the underlying perovskite defects. Consequently, the resulting MAPbI3 solar cells exhibit a high open-circuit voltage of 1.17 V and the concomitant high PCE of 21.84%. In addition, we also use numerical simulations to propose approaches towards achieving high efficiency (PCE>30%) PSCs. Besides expanding the pool of available strategies for improving the efficiency of PSCs, from photon management to interface engineering, our work also offers a systematic guidance for the design and fabrication of high performance photovoltaic devices.

Improved Performance and Stability of Perovskite Solar Modules by Regulating Interfacial Ion Diffusion with Nonionic Cross‐Linked 1D Lead‐Iodide

AbstractLong‐term stability has become the major obstacle for the successful large‐scale application of perovskites devices. Owing to the ionic nature of metal‐halide perovskites, the interfacial ion diffusion can induce irreversible degradation under operational conditions, which presents a great challenge to realize stable perovskite solar modules. Here, a diphenylphosphine oxide compound, ethane‐1,2‐diylbis(diphenylphosphine oxide) (DPPO) is introduced to coordinate with lead iodide and form a cross‐linked 1D Pb3I6‐DPPO (1D‐PbI2) complex. These judiciously designed cross‐linked nonionic low‐dimensional lead halide/organic adducts can passivate the defects of perovskite while acting as a robust ion diffusion barrier, thus significantly improving the electronic quality and intrinsic stability of perovskite films. As a result, high‐performance inverted (p‐i‐n) solar modules with a champion efficiency approaching 19% (a certified stabilized efficiency of 17.8%) for active device areas above 17 cm2 without the use of antisolvents, accompanied by outstanding operational stability under heat stress and continuous illumination are achieved.

Defects in Hybrid Perovskites: The Secret of Efficient Charge Transport (Adv. Funct. Mater. 48/2021)

Charge Transport A combination of optical, electric, and thermal spectroscopy tools shed light on the ground-breaking interaction of defects with free charges in halide perovskite optoelectronic devices. For the first time, in article number 2104467, Artem Musiienko and co-workers demonstrate the effect of defects on diffusion length, lifetime, and mobility of holes and electrons separately. Advanced characterization of charge transport and defects can stimulate new device architectures and material modification pathways.

Are Defects in Lead-Halide Perovskites Healed, Tolerated, or Both?

Are Defects in Lead-Halide Perovskites Healed, Tolerated, or Both?

Hydrogen-Anion-Induced Carrier Recombination in MAPbI3 Perovskite Solar Cells.

Identification and passivation of defect-induced electron-hole recombination centers are currently crucial for improving the efficiency of hybrid perovskite solar cells. Besides general intrinsic defects, experimental reports have indicated that hydrogen interstitials are also abundant in hybrid perovskite layers; however, few reports have evaluated the effect of such defects on the charge carrier recombination and device efficiencies. Here, we reveal that under I-poor synthesis conditions, the negatively charged monatomic hydrogen interstitial, Hi-, will form in the prototypical CH3NH3PbI3 perovskite layer, acting as a detrimental deep-level defect, which leads to efficient electron-hole recombination and lowers the cell performance. We further rationalize that Br doping can mitigate the large atomic displacement caused by the presence of Hi- and hence suppress the formation of the deep localized state. The results advance the knowledge of the deep-level defects in hybrid perovskites and provide useful information for enhancing solar cell performance by defect engineering.

In Situ Perovskitoid Engineering at SnO2 Interface toward Highly Efficient and Stable Formamidinium Lead Triiodide Perovskite Solar Cells.

The black-phase formamidinium lead triiodide (α-FAPbI3) perovskite has turned out to be one of the most efficient light harvesting materials. However, the phase stability of FAPbI3 is a long-standing issue. Herein, we introduce a layer of tetrabutylammonium fluoride (TBAF) on SnO2, which would form an in situ layer of TBAPbI3 perovskitoid at the SnO2/FAPbI3 interface by interacting with PbI2. The results show that this strategy could improve the conductivity of SnO2, passivate the defects in perovskite, improve the phase stability of α-FAPbI3, and retard the nonradiative recombination in the device. As a result, we obtain a champion device with a power conversion efficiency of 23.1% under AM 1.5 G illumination of 100 mW/cm2. The unencapsulated devices can maintain excellent stability under illumination, thermal stress, and humidity conditions, respectively.

Improved Efficiency and Stability of Perovskite Solar Cells Using a Difluorobenzothiadiazole-Based Interfacial Material

The humidity stability of the perovskite solar cell (PSC) is an important issue, which limits its commercialization and practical application. To construct a waterproof interface upon a perovskite film is a valid strategy to improve the stability. In this article, a difluorobenzothiadiazole-based polymer, PffBT4T-C9C13, is employed as an interfacial material and a water barrier on the perovskite by a well-designed deposition method. A uniform perovskite film with a large crystal grain is obtained after the decoration of the polymer owing to its positive impact on the crystal growth. PffBT4T-C9C13 not only protects perovskite from water corrosion but also passivates the surface defects of perovskite. Charge accumulation at the interface is sufficiently suppressed, which is of benefit for the charge transport and extraction. As a result, PSCs with the structure of ITO/TiO2/MA1–xFAxPbI3/PffBT4T-C9C13/spiro-MeOTAD/Ag achieve the highest power conversion efficiency of 20.21%. More importantly, remarkable improvement of the humidity stability is achieved for both perovskite films and PSCs with PffBT4T-C9C13. The unencapsulated device retains more than 80% of its highest power conversion efficiency after 14 days’ aging in humidity of about 50%, and no apparent decomposition of the modified film is observed in 93 days. Therefore, this scheme provides a valuable approach to develop highly efficient and highly stable PSCs.

Inside Front Cover

Shihuai Wang and co‐workers employ a perylene diimide as the interfacial material to passivate surface defects of perovskite and thus improve the performance of perovskite solar cells. They firstly found that the introduction of interfacial material between perovskite layer and hole‐transport layer could enhance the electron transfer across electron transport layer interface more efficiently.The rights of cover image belong to Prof. Yong Hua. image

Impermeable inorganic “walls” sandwiching perovskite layer toward inverted and indoor photovoltaic devices

Interfaces between the perovskite active layer and the charge-transport layers (CTLs) play a critical role in both efficiency and stability of halide-perovskite photovoltaics. One of the major concerns is that surface defects of perovskite could cause detrimental nonradiative recombination and material degradation. In this work, we addressed this challenging problem by inserting ultrathin alkali-fluoride (AF) films between the tri-cation lead-iodide perovskite layer and both CTLs. This bilateral inorganic “walls” strategy makes use of both physical-blocking and chemical-anchoring functionalities of the continuous, uniform and compact AF framework: on the one hand, the uniformly distributed alkali-iodine coordination at the perovskite-AF interfaces effectively suppresses the formation of iodine-vacancy defects at the surfaces, thus reducing the trap-assisted recombination at the perovskite-CTL interfaces and therewith the open-voltage loss; on the other hand, the impermeable AF buffer layers effectively prevent the bidirectional ion migration at the perovskite-CTLs interfaces even under harsh working conditions. As a result, a power-conversion efficiency (PCE) of 22.02% (certified efficiency 20.4%) with low open-voltage deficit (<0.4 V) was achieved for the low-temperature processed inverted planar perovskite solar cells. Exceptional operational stability (500 h, ISOS-L-2) and thermal stability (1000 h, ISOS-D-2) were obtained. Meanwhile, a 35.7% PCE was obtained under dim-light source (1000 lux white LED light) with the optimized device, which is among the best records in perovskite indoor photovoltaics.

Photo-induced defects in MAPbBr3 single crystals

Single crystals of hybrid organic–inorganic halide perovskite have exhibited significantly good stability and a low trap density, leading to advantageous applications in optoelectronics. Even with recent development of high-quality perovskite single crystals, a defect analysis should be addressed to improve device performance in addition to understand the interaction between photo-generated carriers and defects. In this paper, we present a photo-induced defect characterization of CH3NH3PbBr3 (MAPbBr3) perovskite single crystals using an interpretation of photo-current and photo-capacitance measurement. The bulk and the interfacial defect densities of MAPbBr3 crystals with a gold electrode are examined by the characterization of photo-capacitive response under three different wavelengths of light. The transient photo-response of the single crystals reveals the occurrence of carrier trapping and a recombination process. The photo-response under the various light conditions provides a possible origin of defects in MAPbBr3 single crystals. Our comprehensive optoelectronic analysis provides the establishment of the link between the carrier transport and device performance depending on the illuminations. The fundamental understanding of photo-induced defects in perovskites can be helpful to realize the origin of electrical loss and develop highly efficient optoelectronic devices.

Perovskite Light-Emitting Diodes with EQE Exceeding 28% through a Synergetic Dual-Additive Strategy for Defect Passivation and Nanostructure Regulation.

Quasi-2D perovskites have long been considered to have favorable "energy funnel/cascade" structures and excellent optical properties compared with their 3D counterparts. However, most quasi-2D perovskite light-emitting diodes (PeLEDs) exhibit high external quantum efficiency (EQE) but unsatisfactory operating stability due to Auger recombination induced by high current density. Herein, a synergetic dual-additive strategy is adopted to prepare perovskite films with low defect density and high environmental stability by using 18-crown-6 and poly(ethylene glycol) methyl ether acrylate (MPEG-MAA) as the additives. The dual additives containing COC bonds can not only effectively reduce the perovskite defects but also destroy the self-aggregation of organic ligands, inducing the formation of perovskite nanocrystals with quasi-core/shell structure. After thermal annealing, the MPEG-MAA with its CC bond can be polymerized to obtain a comb-like polymer, further protecting the passivated perovskite nanocrystals against water and oxygen. Finally, state-of-the-art green PeLEDs with a normal EQE of 25.2% and a maximum EQE of 28.1% are achieved, and the operating lifetime (T50 ) of the device in air environment is over ten times increased, providing a novel and effective strategy to make high efficiency and long operating lifetime PeLEDs.

Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO3+δ Is a Space‐Charge Phenomenon

AbstractIn displaying accelerated oxygen diffusion along extended defects, (La,Sr)MnO3+δ is an atypical acceptor‐doped perovskite‐type oxide. In this study, 18O/16O diffusion experiments on epitaxial thin films of La0.8Sr0.2MnO3+δ and molecular dynamics (MD) simulations are combined to elucidate the origin of this phenomenon for dislocations: Does diffusion occur along dislocation cores or along space‐charge tubes? Transmission electron microscopy studies of the films revealed dislocations extending from the surface. 18O penetration profiles measured by secondary ion mass spectrometry indicated (slow) bulk diffusion and faster diffusion along dislocations. Oxygen tracer diffusivities obtained for temperatures 873 ≤ T [K] ≤ 973 were over two orders of magnitude higher for dislocations than for the bulk. The activation enthalpy of oxygen diffusion along dislocations, of (2.95 ± 0.21) eV, is surprisingly high relative to that for bulk diffusion, (2.67 ± 0.13) eV. This result militates against fast diffusion along dislocation cores. MD simulations confirmed no accelerated migration of oxide ions along dislocation cores. Faster diffusion of oxygen along dislocations in La0.8Sr0.2MnO3+δ is thus concluded to occur within space‐charge tubes in which oxygen vacancies are strongly accumulated. Reasons for and the consequences of space‐charge zones at extended defects in manganite perovskites are discussed.