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Tin (Sn)‐containing perovskite solar cells (PSCs) have gained significant attention in the field of perovskite optoelectronics due to lower toxicity than their lead‐based counterparts and their potential for tandem applications. However, the lack of stability is a major concern that hampers their development. To achieve the long‐term stability of Sn‐containing PSCs, it is crucial to have a clear and comprehensive understanding of the degradation mechanisms of Sn‐containing perovskites and develop mitigation strategies. This review provides a compendious overview of degradation pathways observed in Sn‐containing perovskites, attributing to intrinsic factors related to the materials themselves and environmental factors such as light, heat, moisture, oxygen, and their combined effects. The impact of interface and electrode materials on the stability of Sn‐containing PSCs is also discussed. Additionally, various strategies to mitigate the instability issue of Sn‐containing PSCs are summarized. Lastly, the challenges and prospects for achieving durable Sn‐containing PSCs are presented. [ABSTRACT FROM AUTHOR]

Metal halide perovskite solar cells (PSCs) have witnessed a swift increase in power conversion efficiency in the past decade, emerging as one of the most promising next‐generation photovoltaic technologies for commercialization and low‐carbon energy generation. Through significant efforts in optimizing the processing techniques, high‐quality perovskite thin films can now be prepared with polycrystalline morphologies consisting of monolayer grains. Nevertheless, defects and microstructural disorders still form at the surface/heterointerface and in the bulk of the films. Post‐treatment of the as‐crystallized films has been intensively investigated for passivating these defects, being proved effective for improving the device performance. In this review, the versatile strategies for post‐treating the surface of perovskite thin films toward morphology control, defect passivation, and band alignment are discussed. The tailored surface properties are correlated to charge dynamics at interfaces and photovoltaic performance of PSCs. Since the perovskite heterostructures prepared by simple post‐treatments may suffer from degradation at high temperatures, the recent advances in preparing phase‐pure and stable perovskite heterostructures are also discussed. Finally, a perspective elaborating future opportunities for further enhancing the efficiency and stability of PSCs is provided. [ABSTRACT FROM AUTHOR]

Quasi‐2D hybrid halide perovskites have drawn considerable attention due to their improved stability and facile tunability compared to 3D perovskites. The expansiveness of possibilities has thus far been limited by the difficulty in incorporating large ligands into thin‐film devices. Here, a bulky bi‐thiophene 2T ligand is focused on to develop a solvent system around creating strongly vertically‐aligned (2T)2(MA)6Pb7I22 (n = 7) quasi‐2D perovskite films. By starting with a poorly coordinating solvent (gamma‐butyrolactone) and adding a small amount of dimethylsulfoxide and methanol, it is found that vertical orientation and z‐uniformity is greatly improved. These are carefully examined and verified using grazing‐incidence wide‐angle X‐ray scattering analysis and advanced optical characterizations. These films are incorporated into champion solar cells that achieve a power conversion efficiency of 13.3%, with a short‐circuit current density of 18.9 mA cm‐2, an open‐circuit voltage of 0.96 V, and a fill factor of 73.8%. Furthermore, the quasi‐2D absorbing layers show excellent stability in moisture, remaining unchanged after hundreds of hours. In addition, 2T is compared with the more common ligands butylammonium and phenylethylammonium in this solvent system to develop heuristics and deeper understanding of how to incorporate large ligands into stable photovoltaic devices. [ABSTRACT FROM AUTHOR]

The frequency of reports utilizing synchrotron‐based grazing incident wide angle X‐ray scattering (GIWAXS) to study metal halide perovskite thin films has exploded recently, as this technique has proven invaluable for understanding several structure‐property relationships that fundamentally limit optoelectronic performance. The GIWAXS geometry and temporal resolution are also inherently compatible with in situ and operando setups (including ISOS protocols), and a relatively large halide perovskite research community has deployed GIWAXS to unravel important kinetic and dynamic features in these materials. Considering its rising popularity, the aim here is to accelerate the required learning curve for new experimentalists by clearly detailing the underlying analytical concepts which can be leveraged to maximize GIWAXS studies of polycrystalline thin films and devices. Motivated by the vast range of measurement conditions offered, together with the wide variety of compositions and structural motifs available (i.e., from single‐crystal and polycrystalline systems, to quantum dots and layered superlatices), a comprehensive framework for conducting effective GIWAXS experiments is outlined for different purposes. It is anticipated that providing a clear perspective for this topic will help elevate the quality of future GIWAXS studies—which have become routine—and provide the impetus required to develop novel GIWAXS approaches to resolve unsettled scientific questions. [ABSTRACT FROM AUTHOR]

The low‐dimensional (LD) perovskites are proven to be capable of blocking moisture erosion and thereby improving the photovoltaic device stability. In this review, the low‐dimensional (LD) perovskite materials are carefully summarized that are induced by A‐position organic substituents, starting from the crystal microstructure and electronic structure of LD (2D, 1D, and 0D) perovskite materials with regulating dimensions, combined with first principles calculation (DFT). By further studying the thermodynamics and dynamics of crystallization nucleation and growth of LD–3D perovskite thin films in the heterojunction region, LD–3D heterojunction perovskite thin films and solar cells with controllable dimensions can be in situ prepared. Various LD–3D perovskite structure photovoltaic devices are systematically summarized, which shows flexible regulation of the energy band structure and carrier transport characteristics, locks the water oxygen corrosion channel with close‐fitting conjugated structure, and improves the long‐term stability of the LD–3D perovskite solar cells. This review is expected to provide some guidance for the perovskite development and multipurpose use through in depth understanding of the structurally dimensional engineering in perovskite photovoltaics. [ABSTRACT FROM AUTHOR]

Quasi‐two‐dimensional perovskite solar cells (quasi‐2D PSCs) have drawn significant attention and are rapidly developing owing to the impressive stability of the materials and devices. However, there are no reliable guidelines for designing and selecting suitable organic spacer cations to achieve high power conversion efficiency (PCE) in quasi‐2D PSCs. Herein, the effects of the spacer cations with different substituents, i.e., benzylamine (PMA), 4‐methoxybenzylamine (p‐MeOPMA), and 4‐fluorobenzylamine (p‐FPMA), on the optoelectronic properties and device performance of quasi‐2D perovskites are systematically investigated. It is found that the spacer cations with different substituents mainly affect the crystal growth and film quality of quasi‐2D perovskites. Interestingly, quasi‐2D perovskites based on p‐MeOPMA or p‐FPMA exhibit poor crystallinity and crystal orientation, while quasi‐2D perovskite based on the unsubstituted PMA shows improved crystallinity and crystal orientation, which enables suppressed trap densities and efficient charge transport. The PMA‐based quasi‐2D perovskite (nominal n = 3) solar cell exhibits the highest PCE of 13.58%. These results demonstrate that the rational regulation of organic spacer cations plays a crucial role in improving the crystallinity and crystal orientation of perovskite films and elucidate key guiding rules for organic spacer cations for high‐performance quasi‐2D PSCs. [ABSTRACT FROM AUTHOR]

Molecular passivation on perovskite surface is an effective strategy to inhibit surface defect‐assisted recombination and reduce nonradiative recombination loss in perovskite solar cells (PSCs). However, the majority of passivating molecules bind to perovskite surface through weak interactions, resulting in weak passivation effects and susceptible to interference from various factors. Especially in carbon‐based perovskite solar cells (C‐PSCs), the molecular passivation effect is more susceptible to disturbance in subsequent harsh preparation of carbon electrodes via blade‐coating route. Herein, bidentate ligand 2,2′‐Bipyridine (2Bipy) is explored to passivate surface defects of CsPbI2.6Br0.4 perovskite films. The results indicate that compared with monodentate pyridine (Py), bidentate 2Bipy shows a stronger chelation with uncoordinated Pb(II) defects and exhibits a greater passivation effect on perovskite surface. As a result, 2Bipy‐modified perovskite films display a significantly boosted photoluminescence lifetime, accompanied by excellent anchoring stability and anti‐dissociation of passivating molecules. Meanwhile, the moisture resistance of the 2Bipy‐modified perovskite films is also significantly enhanced. Consequently, the efficiency of C‐PSCs is improved to 16.57% (Jsc = 17.16 mA cm−2, Voc = 1.198 V, FF = 80.63%). As far as it is known, this value represents a new record efficiency for hole transport material‐free inorganic C‐PSCs. [ABSTRACT FROM AUTHOR]

2D halide perovskites have displayed wide tunability in structure and physicochemical properties through the diversity and versatility of interlayer spacers. However, the interaction between the large spacer and small cation inside the inorganic framework has not been elucidated yet. Herein, the impact of small‐organic cation on the crystallization kinetics, carrier behavior, and the structure distortion of the low‐dimensional Dion–Jacobson (DJ) perovskite materials and solar cells is systematically studied. The formamidium (FA)‐based DJ film exhibits higher crystal orientation and larger crystal domain induced by slower crystallization as compared to methylammonium‐based one, accompanied with lower trap density, more efficient carrier transfer, and higher photovoltaic performance. As a result, the BDAFA2Pb3I10 perovskite solar cell delivers a champion power conversion efficiency up to 15.34%, which is the highest among FA‐based small‐n DJ series. Theoretical simulation results uncover that the smaller tilting and higher rigidity of the octahedra in the FA‐based DJ systems render more outstanding environmental stability, leading to well‐maintained 85% of its efficiency after prolonged storing time of 1020 h at 65 °C. [ABSTRACT FROM AUTHOR]

The relatively lower crystallinity and random orientation of quantum well structures hinder carrier transport and limit the performance of formamidinium (FA) based low‐n 2D perovskite devices. In this work, the crystallization and quantum well orientation are fine tuned to achieve efficient low‐n FA based Ruddlesden–Popper perovskite solar cells. The effects of different ionic additives on the crystallization, orientation, and photovoltaic performance of FA based low‐n 2D perovskites are comparatively investigated. It is found that NH4+ and SCN− can significantly retard the heterogeneous crystallization of low‐n phases in the intermediate state, and drive the templated growth of quantum well structure with vertical orientation. The optimized photovoltaic device based on (BA)2(FA)3Pb4I13 achieved a power conversion efficiency (PCE) of 18.14%, setting the highest record for FA‐based low‐n 2D perovskite solar cells as far as it is known (average n = 4). The unencapsulated device exhibited excellent stability and maintained 93.3% of its original PCE at 85 °C, and 86.3% at 1 Sun illumination after 720 h in humid ambient condition. [ABSTRACT FROM AUTHOR]

Flexible perovskite solar cells (PSC) represent a viable technology for applications requiring high power‐to‐weight ratios, seamless integration onto a variety of shapes, and low embedded energy. Strategies to boost the performance of flexible PSC, which still lag behind their rigid counterparts, include passivation of the perovskite surface with ammonium salts. Herein, the optimization of low‐temperature solution‐processed phenethylammonium iodide (PEAI) layers to passivate triple‐cation perovskite films as an effective strategy for flexible planar PSCs is reported. The best PEAI‐passivated cell delivers a maximum power conversion efficiency of 15.2% in forward scan, which is 22% higher in relative terms compared with nonpassivated devices, due to a major improvement in both open‐circuit voltage and fill factor. Optoelectrical characterization highlights that PEAI films effectively reduce trap‐mediated charge recombination, without hindering charge transport across the perovskite/hole transport layer interface. Light‐soaking stability of nonencapsulated cells with PEAI layers is also greatly enhanced, retaining 80% of the initial power conversion efficiency for twice as long as the reference devices, therefore proving the potential of this material for the development of efficient and durable flexible PSCs. [ABSTRACT FROM AUTHOR]

In the past decade, there has been a rapid development in perovskite solar cells, and their highest device efficiency has reached 25.7%. But their poor stability is still one of the critical factors hindering commercialization. Compared with 3D‐structured perovskites, 2D perovskites have better structural stability especially 2D Dion−Jacobson (D–J) perovskites. However, their degradation mechanism under light is not clear. Herein, the changes in the absorption spectra of D–J perovskites (PDA(FA)n−1PbnI3n−1) under continuous light illumination (100 mW cm−2) are investigated. The absorption spectra of D–J perovskites with different n values change in different degrees after two hours of continuous light illumination. It is found that the absorption intensity near the band edge of all these films has been enhanced, which indicates that some more absorbing species are produced. X‐Ray diffraction patterns confirm that the PDA(FA)n−1PbnI3n−1 2D D–J perovskite is transformed into 3D α‐FAPbI3 after illumination, and further transformed into δ‐FAPbI3 and PbI2. The proposed work contributes to understanding the degradation mechanism of 2D D–J perovskite under illumination and improving the stability of 2D D–J perovskite materials. [ABSTRACT FROM AUTHOR]

2D Ruddlesden–Popper perovskites have risen to prominence as stable and efficient photovoltaic materials because of their structural diversity, rich photophysics, and low moisture ingression. However, thin films processed from stoichiometric precursor solutions possess a broad phase distribution of different number of inorganic layers with random crystal orientation, crippling device performance. The effect of methylammonium chloride (MACl) and 3‐amino‐4‐phenolsulfonic acid (APSA) on the fabrication of perpendicularly oriented (PEA)2MA4Pb5I16 films with narrow phase distribution using antisolvent and hot‐casting processing techniques is investigated. MACl plays a critical role in suppressing parasitic n ≤ 2 and 3D‐like phases. APSA performs the dual function of trap passivation and further narrowing phase polydispersity through strong coordination with Pb2+. Ex situ grazing‐incident wide‐angle X‐Ray scattering (GIWAXS) and ultrafast spectroscopic characterization reveal uniformly mixed‐phase distribution with disordered orientation in antisolvent treated films, while additive‐assisted hot‐casting treatment results in oriented, reverse‐graded phase distribution, i.e., small‐n on the film surface and large‐n at the bottom. Arising thin films enable efficient p–i–n solar cells with an efficiency of 14.34%, and a Voc of 1.20 V, retaining 96% initial efficiency after 1440 h under ambient conditions (RH = 50–60%) without encapsulation. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are considered as one of the most promising alternatives for existing solar cells due to its excellent optoelectronic properties and high efficiency. However, lead has posed a serious issue due to its toxicity which may hinder the commercial use of lead‐based perovskite solar panels/arrays. There has been substantial work progress to find an environment‐friendly alternative metal ion to replace lead. Tin (Sn)‐based PSCs have been successfully synthesized and optimized with high efficiency, making it the most promising active material for lead‐free PSCs. In this review, the role of J–V hysteresis in tin halide PSCs is discussed from the perspective of system structure, working concepts, and interfacial carrier dynamics in detail. The problem of hysteresis in PSCs is closely linked to ion migration, ferroelectric effects, capacitive effects, and trap‐assisted recombination processes, which are highlighted in this review. Further, remediation to reduce the hysteresis by various strategies is explained for tin‐based perovskites. The core focus of this review is to analyze the deterioration of device performance and stability caused due to the generation of defects in the perovskite films, leading to a time‐dependent hysteresis of the current–voltage curves. [ABSTRACT FROM AUTHOR]

Partial tin replacement of lead is expected to be an effective means to fine‐tune the bandgap of Sn–Pb alloyed lead‐halide perovskite to harvest near‐infrared light and thus further increase the efficiency of solar cells based on it, in particular for use as a bottom component cell in the tandem cell design to break through the theoretical Shockley–Queisser (S–Q) limit of the single‐junction solar cells. However, the efficiency of Sn–Pb alloyed perovskite solar cells (PSCs) is still lower than expected owing to the easy oxidation of Sn2+. Herein, a reducing agent 4‐hydrazinobenzoic acid is developed as an additive to suppress the oxidation of Sn2+ and, meanwhile, passivate surface defects. It is found that the optoelectronic performance of Sn–Pb alloyed perovskites is improved as evidenced by the mitigated trap state density and suppressed nonradiative recombination. As a result, the Sn–Pb alloyed PSC efficiency is increased to 21.09%, one of the highest for cells with this bandgap. It is expected that this method is applicable for general Sn–Pb‐based perovskite optoelectronics. [ABSTRACT FROM AUTHOR]

The perovskite photovoltaic field has developed rapidly within a decade. In particular, formamidinium (FA)‐rich perovskite allows a broad absorption spectrum, and is considered to be one of the most promising perovskite materials. Great progress has been achieved, and most recorded high‐efficient perovskite solar cells (PSCs) used the FA‐rich perovskite light absorption layer. However, the black α‐phase formamidinium lead iodide (FAPbI3) perovskite easily transforms into an undesirable δ‐phase at a low temperature. Thus, researchers have put a lot of effort into deeply understanding the phase transformation and stabilization mechanism of FA‐rich perovskite. Herein, the fundamental physical properties of FAPbI3 materials, including crystal structure, phase‐transition temperature, charge‐carrier dynamics, etc. are summarized, and establish a complete phase evolution with temperature by reviewing previous reports. The intrinsic and external factors are subsequently discussed for influencing the stability of FAPbI3 perovskite and the remarkable breakthroughs of FA‐rich PSCs in recent years are reviewed. Moreover, a series of strategies to stabilize FA‐rich perovskite is summarized, including but not limited to compositional engineering, passivating engineering, processing engineering, and strain engineering. Finally, several new viewpoints are provided for improving the efficiency and stability of PSCs. This review may be regarded as a reference project for preparing high‐efficient and stable perovskite photovoltaic devices. [ABSTRACT FROM AUTHOR]

Quasi-2D Ruddlesden--Popper perovskites (RPPs) are candidates for constructing perovskite solar cells (PSCs) with superior stability due to their tolerance to the external environment. Fully understanding the film growth mechanism and structure is crucial to further improve the performance of 2D-PSCs while maintaining device stability. In this work, the origin of Brownian tree-shaped dendrites formed in hot-cast methylammonium chloride (MACl)-doped BA2MAn-1PbnI3n+1 ( = 5) quasi-2D perovskite films are reported. Investigations based on optical, electronic, atomic force, and fluorescence microscopies reveal that the dendrites are assembled from large-n RPPs-dominated grains, while the nondendritic film area is composed of small-n RPPs grains and associated with film surface pits caused by the evaporation of MACl. It is proposed that these dendrites are grown by the diffusion-limited aggregation of the MA-rich intermediate phase domains that initially crystallize from the precursor. The formation of these dendrites in quasi-2D perovskite films upon MACl doping is accompanied by improved organization and crystallinity of the 2D RPPs, which benefits the photovoltaic performance. This work provides new insights into the formation mechanism of quasi-2D perovskite films that should assist device engineering strategies to further improve the performance of 2D PSCs. [ABSTRACT FROM AUTHOR]

The impending commercialization of perovskite solar cells (PSCs) is plodding despite the booming power conversion efficiencies and high stabilities. Most high‐performance, stable PSCs are often processed partially with high‐temperature processes, increasing the cost of production and energy payback time. Low‐temperature‐processed PSCs are crucial as they cut down the expenses lowering the barriers to industrial use. In addition, low‐temperature‐processed methods have a wide range of applicability in flexible devices and for tandem applications with other photovoltaic technologies where the temperature budget is limited. Therefore, making stable PSCs under ambient conditions as well as providing low‐cost fabrication techniques is highly desirable. Here, a detailed review is presented on the development of the low‐temperature process strategies for fabricating highly stable PSCs and perovskite solar modules. The effectiveness of low‐temperature processing in various classes of materials is also discussed. First, the authors introduce some major degradation processes in PSCs. Then, the developments and evolving strategies of notable materials using low‐temperature processing routes and a correlation with stability are summarized. A few general trends which are related to stability are also discussed. Overall, this review contributes to a better understanding of the status of low‐temperature‐processed cells and modules. [ABSTRACT FROM AUTHOR]

Solution‐processed metal halide perovskites have the advantages of a tunable bandgap, excellent charge transport properties, and suitable exciton binding energy. They therefore emerge as promising semiconductors for efficient perovskite solar cells (PSCs) and bright perovskite light‐emitting diodes (PLEDs). In addition, these devices possess a similar planar–heterojunction architecture, thus novel dual‐functional perovskite light‐emitting solar cells (PLESCs) that can realize electrical‐to‐optical and optical‐to‐electrical conversion on one device are developed. To date, high‐performance PLESCs with 17.2% electroluminescence external quantum efficiency and 25.2% power conversion efficiency are achieved using a holistic optimization approach. However, a comprehensive review focusing on dual‐functional PLESCs with discussion on their development and limitations, remains lacking. Herein, the rapid progress in PLESCs, including 0D quantum dot, 2D Ruddlesden–Popper, and 3D bulk perovskite devices, is reviewed. First, the fundamental understanding of the device structure and working principle of PLESCs is overviewed. Second, the state‐of‐the‐art developments for simultaneously achieving high‐efficiency PSCs and PLEDs, focusing on defect passivation, interface optimization, energy level alignment, and dimensional control, are comprehensively summarized. Finally, the authors offer some perspectives for future trends in the development of promising PLESCs, which can provide guidelines for this emerging field. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) based on 2D/3D heterostructures show great potential to combine the advantages of the high efficiency of 3D perovskites and the high stability of 2D perovskites. However, an in‐depth understanding of the organic‐spacer effects on the 2D quantum well (QW) structures and electronic properties at the 2D/3D interfaces is yet to be fully achieved, especially in the case of 2D perovskites based on diammonium spacers/ligands. Here, a series of diammonium spacers is considered for the construct ion 2D/3D perovskite heterostructures. It is found that the chemical structure and concentration of the spacers can dramatically affect the characteristics of the 2D capping layers, including their phase purity and orientation. Density functional theory calculations indicate that the spacer modifications can induce shifts in the energy‐level alignments at the 2D/3D interfaces and therefore influence the charge‐transfer characteristics. The strong intermolecular interactions between the 2,2‐(ethylenedioxy)bis(ethylammonium) (EDBE) cations and inorganic [PbI6]4− slabs facilitate a controlled deposition of a phase‐pure QW structure (n = 1) with a horizontal orientation, which leads to better surface passivation and carrier extraction. These benefits endow the EDBE‐based 2D/3D devices with a high power conversion efficiency of 22.6% and remarkable environmental stability, highlighting the promise of spacer‐chemistry design for high‐performance 2D/3D PSCs. [ABSTRACT FROM AUTHOR]

Long‐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. [ABSTRACT FROM AUTHOR]

2D/3D mixed tin (Sn)‐based perovskites serving as excellent active layers possess a potential for enhancing film/device stabilities, open‐circuit voltage, and power conversion efficiency (PCE) of perovskite solar cells (PSCs). Unfortunately, the poor morphology and low film coverage of these 2D/3D perovskites jeopardize their device performance and stability. Herein, doping of hydroxyl‐rich d‐sorbitol into hole transport layer poly(3,4‐ethenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) can effectively address the PEDOT:PSS/perovskite interfacial issues. The multihydroxyl groups from d‐sorbitol can sufficiently anchor iodide ions ([SnI6]4− or free I−) of PEA0.1(FA0.75MA0.25)0.9SnI3 perovskite via hydrogen bond, which not only introduces more nucleation sites with improved crystallinity along the preferential crystal orientations, but also reduces the trap states' density and suppresses the iodide ions' migration. In the meanwhile, the content of SnI2 is reduced in the resulting perovskite films. All of these are conducive to form compact and smooth high‐quality perovskite films with less traps and enhanced stability. Benefitting from these, an inverted PSC with a champion PCE of 10.46% and a lifetime of 700 h (25% attenuation in N2) is eventually achieved. This work provides a promising approach to manufacture highly efficient and stable Sn‐based PSCs based on 2D/3D mixed perovskites. [ABSTRACT FROM AUTHOR]

Lead‐halide perovskites (LHPs), in the form of both colloidal nanocrystals (NCs) and thin films, have emerged over the past decade as leading candidates for next‐generation, efficient light‐emitting diodes (LEDs) and solar cells. Owing to their high photoluminescence quantum yields (PLQYs), LHPs efficiently convert injected charge carriers into light and vice versa. However, despite the defect‐tolerance of LHPs, defects at the surface of colloidal NCs and grain boundaries in thin films play a critical role in charge‐carrier transport and nonradiative recombination, which lowers the PLQYs, device efficiency, and stability. Therefore, understanding the defects that play a key role in limiting performance, and developing effective passivation routes are critical for achieving advances in performance. This Review presents the current understanding of defects in halide perovskites and their influence on the optical and charge‐carrier transport properties. Passivation strategies toward improving the efficiencies of perovskite‐based LEDs and solar cells are also discussed. [ABSTRACT FROM AUTHOR]

Recent progress in the engineering and fabrication optimization of hybrid perovskite solar cells (PSCs) has led to power conversion efficiencies (PCEs) of up to 25.2%. The properties of perovskite solutions enable low‐temperature, scalable coating methods that are compatible with the roll‐to‐roll (R2R) fabrication process. Despite this, there is still a significant lag in efficiency in large‐area devices fabricated using the R2R process, which achieves PCEs of 50% of the record value. Direct translation of research results to large‐scale commercially acceptable levels is crucial for commercialization, along with long‐term durability and processing reproducibility of the different device layers. Herein, the recent progress of several coating and R2R processes for the formation of PSC layers, detailing the key variables involved in the process, with an emphasis on the nucleation and crystallization of the perovskite film, is considered. The barriers and challenges in producing high‐quality perovskite films and improving the stability of devices are discussed. In addition, stability protocols for PSCs are discussed as they are key to unifying PSC stability and performance assessment, which is required to gain a better understanding of the different compounds and layers used in cell fabrication and the approaches necessary for their optimization. [ABSTRACT FROM AUTHOR]

New structural type of 2D AA′n−1MnX3n+1 type halide perovskites stabilized by symmetric diammonium cations has attracted research attention recently due to the short interlayer distance and better charge‐transport for high‐performance solar cells (PSCs). However, the distribution control of quantum wells (QWs) and its influence on optoelectronic properties are largely underexplored. Here effective phase‐alignment is reported through dynamical control of film formation to improve charge transfer between quantum wells (QWs) for 2D perovskite (BDA)(MA)n‐1PbnI3n+1 (BDA = 1,4‐butanediamine, 〈n〉 = 4) film. The in situ optical spectra reveal a significantly prolonged crystallization window during the perovskite deposition via additive strategy. It is found that finer thickness gradient by n values in the direction orthogonal to the substrate leads to more efficient charge transport between QWs and suppressed charge recombination in the additive‐treated film. As a result, a power conversion efficiency of 14.4% is achieved, which is not only 21% higher than the control one without additive treatment, but also one of the high efficiencies of the low‐n (n ≤ 4) AA′n−1MnX3n+1 PSCs. Furthermore, the bare device retains 92% of its initial PCE without any encapsulation after ambient exposure for 1200 h. [ABSTRACT FROM AUTHOR]

Low‐dimensional‐networked (LDN) perovskites denote materials in which the molecular structure adopts 2D, 1D, or 0D arrangement. Compared to conventional 3D structured lead halide perovskite (chemical formula: ABX3 where A: monovalent cations, B: divalent cations, X: halides) that have been studied widely as light absorber and used in current state‐or‐the‐art solar cells, LDN perovskite have unique properties such as more flexible crystal structure, lower ion transport mobility, robust stability against environmental stress such as moisture, thermal, etc., making them attractive for applications in optoelectronic devices. Since 2014, reports on LDN perovskite materials used in perovskite solar cells, light emitting diodes (LEDs), luminescent solar concentrators (LSC), and photodetectors have been reported, aiming to overcome the obstacles of conventional 3DN perovskite materials in these optoelectronic devices. In this review, the variable ligands used to make LDN perovskite materials are summarized, their distinct properties compared to conventional 3D perovskite materials. The research progress of optoelectronic devices including solar cells, LEDs, LSCs, and photodetectors that used different LDNs perovskite, the roles and working mechanisms of the LDN perovskites in the devices are also demonstrated. Finally, key research challenges and outlook of LDN materials for various optoelectronic applications are discussed. [ABSTRACT FROM AUTHOR]

The instability of 3D perovskite and the low power conversion efficiency (PCE) of 2D perovskite limit the development of perovskite solar cells (PSCs). Using 2D perovskite to passivate 3D perovskite thin films by heterojunction engineering has become an effective strategy to develop stable and efficient PSCs. Therefore, it is important to find suitable 2D perovskite passivation materials. Herein, a 2D/3D heterojunction perovskite is formed in situ by introducing a long‐chain alkyl phenylbutylammonium (PBA+) cation. The 2D perovskite has the property of n = 2, which passivates the surface defects of the 3D perovskite, resulting in enhanced photoluminescence intensity and prolonged carrier lifetime. Moreover, the 2D layer changes the interface contact and energy‐level arrangement, making it a more n‐type semiconductor, which facilitates the electron transfer between perovskites and electron transport. This strategy significantly improves the open circuit voltage (Voc) and fill factor (FF) of the devices without sacrificing current, and the PCE is improved from 19.22% to 21.76%. The hydrophobic PBA+‐based 2D layer also improves the humidity stability of the films and enhances the working stability of the device. The PCE of the champion heterojunction perovskite device remains 87% of its initial value after illumination for 1000 h. The results show that heterojunction engineering plays an important role in the preparation of efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

In the last 10 years, organic–inorganic hybrid perovskite solar cells have achieved unprecedented advances, to the point where they now exhibit extremely high efficiency. However, long‐term stability and areal scalability limitations impede the commercial application of perovskite materials, and appropriate diagnosistic tools have become necessary to evaluate perovskite materials. Characterization of perovskite materials is regularly misinterpretated, due to unique intrinsic and extrinsic factors: degradation from the measurement source, ion migration, phase transition, and separation. Herein, studies on perovskites are reviewed that have used advanced characterization tools to overcome characterization challenges. Cryogenic temperature assisted measurements mitigate degradation or phase transitions induced by the measurement source. In situ measurements can track the variation of perovskite materials depending on external stimuli. Spatial material properties are able to be evaluated by the use of multidimensional mapping techniques. An overview of these advanced characterization tools that can overcome the challenges associated with established tools provides the opportunity for further understanding perovskite materials and solving the remaining challenges on the road to commercialization. [ABSTRACT FROM AUTHOR]

Heterogeneous organic‐inorganic halide perovskites possess inherent non‐uniformities in bandgap that are sometimes engineered and exploited on purpose, like in quasi‐2D perovskites. In these systems, charge carrier and excitation energy migration to lower‐bandgap sites are key processes governing luminescence. The question, which of them dominates in particular materials and under specific experimental conditions, still remains unanswered, especially when charge carriers comprise excitons. In this study transient absorption (TA) and transient photoluminescence (PL) techniques are combined to address the excited state dynamics in quasi‐2D and other heterogeneous perovskite structures in broad temperature range, from room temperature down to 15 K. The data provide clear evidence that charge carrier transfer rather than energy migration dominates in heterogeneous quasi‐2D perovskite films. [ABSTRACT FROM AUTHOR]

Organic–inorganic halide perovskite solar cells (PSCs) are a new class of photovoltaic devices, which have attracted increasing interests due to high efficiency, low cost, and simple fabrication process. Although a remarkable enhancement in power conversion efficiency (PCE) has been achieved in the last decade, the stability issue, including high water/heat sensitivity and UV light‐induced degradation, has become one of the main obstacles for practical applications of PSCs. Herein, hydrophobic butyl acrylate with CO and CC groups is reported as a new additive to enhance the PCE and moisture/thermal stability of CH3NH3PbI3‐based PSCs, which improves the quality of the perovskite film by promoting defect passivation, constructing a suitable energy‐level alignment, and increasing the charge carrier lifetime in PSCs. Such an additive is easily introduced into PSCs without the need for thermal treatment, which is typically required by other additives, causing a negative effect on the efficiency. The CH3NH3PbI3‐based PSC with butyl acrylate additive shows a superior PCE of 20.0%, 19% higher than that of the unmodified device (16.8%), as well as much improved moisture/thermal stability. Herein, a facile way is provided to enhance the PCE and stability of CH3NH3PbI3‐based PSCs simultaneously, which facilitates the commercialization of PSCs. [ABSTRACT FROM AUTHOR]

Perovskite‐based photovoltaics (PVs) have garnered tremendous interest, enabling power conversion efficiencies exceeding 25%. Although much of this success is credited to the exploration of new compositions, defects passivation and process optimization, environmental stability remains an important bottleneck to be solved. The underlying mechanisms of thermal and humidity‐induced degradation are still far from a clear understanding, which poses a severe limitation to overcome the stability issues. Herein, in situ X‐ray diffraction (XRD), in operando liquid‐cell transmission electron microscopy (TEM) and ex situ solid‐state (ss)NMR spectroscopy are combined with time‐resolved spectroscopies to reveal new insights about the degradation mechanisms of methylammonium lead halide (MAPbI3) under 85% relative humidity (RH) at different length scales. Liquid‐cell TEM enables the live visualizations from meso‐to‐nanoscale transformation between the perovskite particles and water molecules, which are corroborated by the changes in local structures at sub‐nanometer distances by ssNMR and longer range by XRD. This work clarifies the role of surface defects and the significance of their passivation to prevent hydration and decomposition reactions. [ABSTRACT FROM AUTHOR]

Metal halide perovskite solar cells (PSCs) have emerged as promising next‐generation photovoltaic devices with the maximum output efficiency exceeding 25%. Despite significant advances, there are many challenges to achieve high efficiency, stability, and low‐cost simultaneously. Combating these challenges depends on developing novel materials and modifying conventional device components. Carbon nanotubes (CNTs) have attracted considerable attention for fabricating efficient PSCs owing to their remarkable electrical, optical, and mechanical properties. With their multifunctional features, CNTs can play a wide range of roles and offer unique benefits in various components in PSCs to improve device performance and durability. Here, recent progress concerning the utilizations of CNTs as transparent conductive electrodes, charge‐transporter, perovskite additives, interlayers, hole‐transporting materials, and back electrodes in PSCs is comprehensively reviewed. The application of CNTs toward the development of 1D and 2D flexible PSCs is also discussed. A summary of current challenges and prospective on future research directions of employing CNTs to realize high‐performance PSCs is presented. [ABSTRACT FROM AUTHOR]

In the past decade, the perovskite solar cell (PSC) has attracted tremendous attention thanks to the substantial efforts in improving the power conversion efficiency from 3.8% to 25.5% for single‐junction devices and even perovskite‐silicon tandems have reached 29.15%. This is a result of improvement in composition, solvent, interface, and dimensionality engineering. Furthermore, the long‐term stability of PSCs has also been significantly improved. Such rapid developments have made PSCs a competitive candidate for next‐generation photovoltaics. The electron transport layer (ETL) is one of the most important functional layers in PSCs, due to its crucial role in contributing to the overall performance of devices. This review provides an up‐to‐date summary of the developments in inorganic electron transport materials (ETMs) for PSCs. The three most prevalent inorganic ETMs (TiO2, SnO2, and ZnO) are examined with a focus on the effects of synthesis and preparation methods, as well as an introduction to their application in tandem devices. The emerging trends in inorganic ETMs used for PSC research are also reviewed. Finally, strategies to optimize the performance of ETL in PSCs, effects the ETL has on J–V hysteresis phenomenon and long‐term stability with an outlook on current challenges and further development are discussed. [ABSTRACT FROM AUTHOR]

Solar cells based on metal halide perovskites have reached a power conversion efficiency as high as 25%. Their booming efficiency, feasible processability, and good compatibility with large‐scale deposition techniques make perovskite solar cells (PSCs) desirable candidates for next‐generation photovoltaic devices. Despite these advantages, the lifespans of solar cells are far below the industry‐needed 25 years. In fact, numerous PSCs throughout the literature show severely hampered stability under illumination. Herein, several photoinduced degradation mechanisms are discussed. With light radiation, the organic–inorgainc perovskites are prone to phase segregation or chemical decomposition; the oxide electron transport layers (ETLs) tend to introduce new defects at the interface; the commonly used small molecules‐based hole transport layers (HTLs) typically suffer from poor photostability and dopant diffusion during device operation. It has been demonstrated the photoinduced degradation can take place in every functional layer, including the active layer, ETL, HTL, and their interfaces. An overview of these degradation categories is provided in this review, in the hope of encouraging further research and optimization of relevant devices. [ABSTRACT FROM AUTHOR]

Over 25% efficiencies have been achieved by organic–inorganic hybrid perovskite solar cells (PSCs). However, their practical applications are limited by the instability of the hybrid perovskite materials. Replacing hybrid perovskites with inorganic CsPbX3 perovskites shows great promise to address the above issue and much progress has been made. To achieve high efficiency and stable inorganic CsPbX3 PSCs, organic molecular engineering has been playing a vital role. Herein, the progress of the organic molecular engineering in inorganic CsPbX3 PSCs is systematically reviewed. First, structure evolution induced by organic molecular engineering for inorganic CsPbX3 perovskites is demonstrated. Then, organic molecular engineering in CsPbX3 PSCs is categorized and reviewed (alloying in perovskite structures, as sacrificial agents, forming 2D structures, and modifying surfaces and interfaces). Finally, future research directions are suggested to further improve the performance of inorganic PSCs. [ABSTRACT FROM AUTHOR]

Tailoring the organic spacing cations enables developing new Ruddlesden–Popper (RP) perovskites with tunable optoelectronic properties and superior stabilities. However, the formation of highly crystallized RP perovskites can be hindered when the structure of organic cations become complex. Strategies to regulate crystal growing process and grains quality remain to be explored. In this study, mixing Rb+ ions in precursor solution is reported to significantly promote the crystallinity of phenylethylammonium (PEA+) based RP perovskites without impacting on the major orientation of perovskite grains, which leads to increased power conversion efficiencies from 12.5% to 14.6%. It is found that the added Rb+ ions prefer to accumulate at crystal growing front and form Rb+ ions‐rich region, which functions as mild crystal growth inhibitor to retard the absorption and diffusion of organic cations at growing front and hence regulates crystal growing rate. The retarded crystal growth benefits PEA‐based RP perovskite films with elevated crystal qualities and prolonged carrier recombination lifetimes. Similar increased crystallinity and photovoltaic performance are achieved in other RP perovskites with non‐linear organic cations such as phenylmethylammonium (PMA+), 1‐(2‐naphthyl)‐methanammoniun (NMA+) by adding Rb+ ions, demonstrating using a small amount of growth inhibitor as a general route to regulate crystal growth. [ABSTRACT FROM AUTHOR]

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded 25%, showing great potential in the photovoltaic field. However, PSCs often show anomalous current density–voltage (J–V) hysteresis behavior in the forward and reverse scanning directions, which makes it impossible to accurately evaluate the performance of PSCs. Therefore, it is necessary to clearly understand the mechanism of hysteresis and suppress the hysteresis. Herein, the J–V hysteresis behavior in PSCs and strategies to suppress hysteresis is focused: first, the various factors that affect J–V hysteresis in PSCs are summarized. And the mechanism behind the various possible origins of hysteresis and the challenges encountered are explored. Then, the strategies to suppress or eliminate the hysteresis are summarized, including optimizing the perovskite light‐absorbing layer, improving the performance of the carrier transport layer and interface engineering. Finally, insights on the future development of the hysteresis are also provided. [ABSTRACT FROM AUTHOR]

Cesium‐based all‐inorganic halide perovskites solar cells (PSCs) have recently attracted increasing attention. Currently, due to the existence of high defects density and unoptimized interfacial morphology, "state‐of‐the‐art" performances of all‐inorganic PSCs are still far away from their theoretical limits. Although commonly used two‐step passivation methods can effectively passivate the perovskite surface, they will inevitably detriment the original perovskite morphology due to the use of weak‐polarity solvents. This will potentially result in the unintentional doping, uncontrollable interfacial band alignment, and the additional defects formation. Hence, a spontaneous interfacial manipulation (SIM) method is developed to self‐organize a 2D/3D multidimensional perovskite top interface. It is demonstrated that the spontaneously formed ultrathin 2D perovskite can not only eliminate the interfacial defects, but also effectively prevent moisture penetration. As a result, a significant power conversion efficiency enhancement from 13.64% to over 18% is obtained along with greatly extended device lifetime, for CsPbIxBr3‐x‐based all‐inorganic PSC. [ABSTRACT FROM AUTHOR]

Despite a higher power conversion efficiency (PCE) than other lead‐free perovskite solar cells (PSCs) due to intrinsically excellent optoelectronic properties and suitable bandgaps of tin (Sn) perovskites, Sn‐based PSCs still suffer from issues of stability and efficiency for practical applications. Herein, a novel strategy of tuning perovskite crystal orientation toward ≈45° with respect to the substrate by doping 2,3‐diaminopropionic acid monohydrochloride (2,3‐DAPAC) into formamidinium tin iodide (FASnI3) is proposed, which facilitates charge transport in the perovskite film and consequent device performances. In addition, the incorporation of 2,3‐DAPAC into FASnI3 enables dense and smooth high‐quality perovskite films with less Sn vacancies. Applications of the 2,3‐DAPAC‐treated FASnI3 films into PSCs acquire a champion PCE of 7.23%, showing 37.2% enhancement compared with 5.27% of the control device. Moreover, the storage stabilities of both perovskite films and PSCs are significantly prolonged with improved film quality. [ABSTRACT FROM AUTHOR]

Layered hybrid perovskites have emerged as a promising alternative to stabilizing hybrid organic–inorganic perovskite materials, which are predominantly based on Ruddlesden‐Popper structures. Formamidinium (FA)‐based Dion‐Jacobson perovskite analogs are developed that feature bifunctional organic spacers separating the hybrid perovskite slabs by introducing 1,4‐phenylenedimethanammonium (PDMA) organic moieties. While these materials demonstrate competitive performances as compared to other FA‐based low‐dimensional perovskite solar cells, the underlying mechanisms for this behavior remain elusive. Here, the structural complexity and optoelectronic properties of materials featuring (PDMA)FAn–1PbnI3n+1 (n = 1–3) formulations are unraveled using a combination of techniques, including X‐ray scattering measurements in conjunction with molecular dynamics simulations and density functional theory calculations. While theoretical calculations suggest that layered Dion‐Jacobson perovskite structures are more prominent with the increasing number of inorganic layers (n), this is accompanied with an increase in formation energies that render n > 2 compositions difficult to obtain, in accordance with the experimental evidence. Moreover, the underlying intermolecular interactions and their templating effects on the Dion‐Jacobson structure are elucidated, defining the optoelectronic properties. Consequently, despite the challenge to obtain phase‐pure n > 1 compositions, time‐resolved microwave conductivity measurements reveal high photoconductivities and long charge carrier lifetimes. This comprehensive analysis thereby reveals critical features for advancing layered hybrid perovskite optoelectronics. [ABSTRACT FROM AUTHOR]

Tandem solar cells (TSCs) comprising stacked narrow‐bandgap and wide‐bandgap subcells are regarded as the most promising approach to break the Shockley–Queisser limit of single‐junction solar cells. As the game‐changer in the photovoltaic community, organic–inorganic hybrid perovskites became the front‐runner candidate for mating with other efficient photovoltaic technologies in the tandem configuration for higher power conversion efficiency, by virtue of their tunable and complementary bandgaps, excellent photoelectric properties, and solution processability. In this review, a perspective that critically dilates the progress of perovskite material selection and device design for perovskite‐based TSCs, including perovskite/silicon, perovskite/copper indium gallium selenide, perovskite/perovskite, perovskite/CdTe, and perovskite/GaAs are presented. Besides, all‐inorganic perovskite CsPbI3 with high thermal stability is proposed as the top subcell in TSCs due to its suitable bandgap of ≈1.73 eV and rapidly increasing efficiency. To minimize the optical and electrical losses for high‐efficiency TSCs, the optimization of transparent electrodes, recombination layers, and the current‐matching principles are highlighted. Through big data analysis, wide‐bandgap perovskite solar cells with high open‐circuit voltage (Voc) are in dire need in further study. In the end, opportunities and challenges to realize the commercialization of TSCs, including long‐term stability, area upscaling, and mitigation of toxicity, are also envisioned. [ABSTRACT FROM AUTHOR]

The notoriously poor stability of organic–inorganic hybrid perovskite solar cells is a crucial issue restricting the commercial application of such burgeoning technology. Passivation of bulk perovskite absorber by fluorinated aromatic ammonium salt via low‐dimensional perovskites has been proved to be an effective way of improving stability and efficiency. Herein, the influence of fluorination position (ortho‐, meso‐, and para‐) on the aromatic moiety is studied in terms of their dipole moments and the ability to reduce defect density, extend carrier lifetimes, and assist charge transfer. In addition to the improved power conversion efficiency (PCE) from 19.17% to above 20%, the device treated with 2‐(o‐fluorophenyl)ethylamine iodide exhibits a remarkable open‐circuit voltage (VOC) of 1.21 V. While the 2‐(p‐fluorophenyl)ethylamine iodide‐treated device shows only 1% loss of its initial value under ambient atmosphere (with RH of 10–30%) without encapsulation for 1440 h storage. The molecular structure of fluorinated aromatic cations plays multiple roles in passivating the interface of the perovskite device. [ABSTRACT FROM AUTHOR]

2D Ruddlesden–Popper perovskites (RPPs) are emerging as potential challengers to their 3D counterpart due to superior stability and competitive efficiency. However, the fundamental questions on energetics of the 2D RPPs are not well understood. Here, the energetics at (PEA)2(MA)n−1PbnI3n+1/[6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) interfaces with varying n values of 1, 3, 5, 40, and ∞ are systematically investigated. It is found that n–n junctions form at the 2D RPP interfaces (n = 3, 5, and 40), instead of p–n junctions in the pure 2D and 3D scenarios (n = 1 and ∞). The potential gradient across phenethylammonium iodide ligands that significantly decreases surface work function, promotes separation of the photogenerated charge carriers with electron transferring from perovskite crystal to ligand at the interface, reducing charge recombination, which contributes to the smallest energy loss and the highest open‐circuit voltage (Voc) in the perovskite solar cells (PSCs) based on the 2D RPP (n = 5)/PCBM. The mechanism is further verified by inserting a thin 2D RPP capping layer between pure 3D perovskite and PCBM in PSCs, causing the Voc to evidently increase by 94 mV. Capacitance–voltage measurements with Mott–Schottky analysis demonstrate that such Voc improvement is attributed to the enhanced potential at the interface. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have received great attention due to their outstanding performance and their low processing costs. To boost their performance, one approach is to reinforce the built‐in electric field (BEF) to promote oriented carrier transport. The BEF is maximized by reinforcing the work function difference between cathode and anode (Δμ1) and increasing the work function difference between lower and upper surfaces of perovskite film (Δμ2) via introduction of electric dipole molecules, denoted as PTFCN and CF3BACl. The synergistic reinforcement of BEF improves charge transport and collection, and realizes markedly high photovoltaic performances with the best power conversion efficiency (PCE) up to 21.5%, a growth of 15.6% as compared to the control device, which is higher than the superposition of improvements achieved by either raising Δμ1 or Δμ2. Importantly, dual‐functional CF3BACl not only supplies dipole effect for tuning the surface potential of perovskite but offers hydrophobic trifluoride group toward the long‐term stable unencapsulated PSCs retaining more than 95% PCE after storing 2000 h under ambient conditions. This work demonstrates the synergistic effect of Δμ1 and Δμ2, providing an effective strategy for the further development of PSC in terms of photovoltaic conversion and stability. [ABSTRACT FROM AUTHOR]

As perovskite solar cells (PSCs) are highly efficient, demonstration of high‐performance printed devices becomes important. 2D/3D heterostructures have recently emerged as an attractive way to relieving the film inhomogeneity and instability in perovskite devices. In this work, a 2D/3D ensemble with 2D perovskites self‐assembled atop 3D methylammonium lead triiodide (MAPbI3) via a one‐step printing process is shown. A clean and flat interface is observed in the 2D/3D bilayer heterostructure for the first time. The 2D perovskite capping layer significantly suppresses nonradiative charge recombination, resulting in a marked increase in open‐circuit voltage (VOC) of the devices by up to 100 mV. An ultrahigh VOC of 1.20 V is achieved for MAPbI3 PSCs, corresponding to 91% of the Shockley–Queisser limit. Moreover, notable enhancement in light, thermal, and moisture stability is obtained as a result of the protective barrier of the 2D perovskites. These results suggest a viable approach for scalable fabrication of highly efficient perovskite solar cells with enhanced environmental stability. [ABSTRACT FROM AUTHOR]

2D Ruddlesden–Popper perovskites (RPPs) have recently drawn significant attention because of their structural variability that can be used to tailor optoelectronic properties and improve the stability of derived photovoltaic devices. However, charge separation and transport in 2D perovskite solar cells (PSCs) suffer from quantum well barriers formed during the processing of perovskites. It is extremely difficult to manage phase distributions in 2D perovskites made from the stoichiometric mixtures of precursor solutions. Herein, a generally applicable guideline is demonstrated for precisely controlling phase purity and arrangement in RPP films. By visually presenting the critical colloidal formation of the single‐crystal precursor solution, coordination engineering is conducted with a rationally selected cosolvent to tune the colloidal properties. In nonpolar cosolvent media, the derived colloidal template enables RPP crystals to preferentially grow along the vertically ordered alignment with a narrow phase variation around a target value, resulting in efficient charge transport and extraction. As a result, a record‐high power conversion efficiency (PCE) of 14.68% is demonstrated for a (TEA)2(MA)2Pb3I10 (n = 3) photovoltaic device with negligible hysteresis. Remarkably, superior stability is achieved with 93% retainment of the initial efficiency after 500 h of unencapsulated operation in ambient air conditions. [ABSTRACT FROM AUTHOR]

Lead halide perovskite solar cells now show excellent efficiencies and encouraging levels of stability. Further improvements in performance require better control of the trap states which are considered to be associated with vacancies and defects at crystallite surfaces. Herein, a reflection on the ways in which these traps can be mitigated is presented by improving the quality of the perovskite layer and interfaces in fully assembled device configurations. In this review, the most recent design strategies reported in the literature, which have been explored to tune grain orientation, to passivate defects, and to improve charge‐carrier lifetimes, are presented. Specifically, the advances made with single‐cation, mixed‐cation and/or mixed‐halide, and 3D/2D bilayer‐based light absorbers are discussed. The interfacial, compositional, and band alignment engineering along with their consequent effects on the open‐circuit voltage, power conversion efficiency, and stability are a particular focus. [ABSTRACT FROM AUTHOR]

Additives are widely adopted for efficient, stable, and hysteresis‐free perovskite solar cells and play an important role in various breakthroughs of perovskite solar cells (PSCs). Herein the various additives adopted for PSCs are reviewed and their functioning mechanism and influence on device performance is described. The main roles of additives, modulating morphology of perovskite films, stabilizing phase of formamidinium (FA) and cesium (Cs)‐based perovskites, adjusting energy level alignment in PSCs, suppressing nonradiative recombination in perovskites, eliminating hysteresis, enhancing operational stability of PSCs, are summarized. [ABSTRACT FROM AUTHOR]

For the fabrication of low‐dimensional perovskite solar cells, understanding the effect of precursor preparation on film formation is critical to achieve high‐quality perovskite film and, therefore, high efficiency in related solar devices. Herein, the two methods to prepare phenethylammonium‐based mixed perovskite precursors with the same chemical composition are reported. These methods are called 1) different phase (DP) and 2) same phase (SP) methods as the former involves the mixing of a 3D perovskite precursor with a 2D perovskite precursor, whereas the latter involves the mixing of quasi‐2D perovskite precursors. The films prepared by these methods are characterized by X‐ray diffraction, Kelvin probe force microscopy, and scanning electron microscopy, revealing different perovskite structures. The power conversion efficiency (PCE) of the champion cells by DP and SP methods reaches 19.1% and 18.9%, respectively. Results of the aging test show a dramatic improvement in the stability of SP perovskite devices maintaining 86% of its initial performance after exposure to a relative humidity (RH) 8 ± 5% for 1000 hr and over 80% of its initial PCE after continuous 1 sun illumination (including UV) at RH 70%. The new insights provided by this work are important to design perovskite precursor preparation methods for the best device performance and stability. [ABSTRACT FROM AUTHOR]

Due to their superior environmental stability, utilization of low‐dimensional perovskites in organometal halide solar cells (OMHSCs) has seen a sharp increase. Herein, a method to form 1D pyrrolidinium lead iodide (PyPbI3) in situ atop photoactive 3D methylammonium lead iodide (MAPbI3) using pyrrolidine posttreatment is reported. As compared with 3D MAPbI3, 1D PyPbI3 has a wider bandgap and is more environmentally stable, and it serves as a tunneling contact to mitigate charge carrier recombination and as a robust barrier against environmental degradation when incorporated into OMHSCs. Accordingly, power conversion efficiencies of the resulting MAPbI3 devices are enhanced from an average of 14.86% ± 0.65% to 15.9% ± 0.58% and their shelf‐life stability is significantly prolonged. [ABSTRACT FROM AUTHOR]

High‐efficiency perovskite‐based solar cells can be fabricated via either solution‐processing or vacuum‐based thin‐film deposition. However, both approaches limit the choice of materials and the accessible device architectures, due to solvent incompatibilities or possible layer damage by vacuum techniques. To overcome these limitations, the lamination of two independently processed half‐stacks of the perovskite solar cell is presented in this work. By laminating the two half‐stacks at an elevated temperature (≈90 °C) and pressure (≈50 MPa), the polycrystalline perovskite thin‐film recrystallizes and the perovskite/charge transport layer (CTL) interface forms an intimate electrical contact. The laminated perovskite solar cells with tin oxide and nickel oxide as CTLs exhibit power conversion efficiencies of up to 14.6%. Moreover, they demonstrate long‐term and high‐temperature stability at temperatures of up to 80 °C. This freedom of design is expected to access both novel device architectures and pairs of CTLs that remain usually inaccessible. [ABSTRACT FROM AUTHOR]