The trap states at grain boundaries (GBs) within polycrystalline perovskite films deteriorate their optoelectronic properties, making GB engineering particularly important for stable high‐performance ...optoelectronic devices. It is demonstrated that trap states within bulk films can be effectively passivated by semiconducting molecules with Lewis acid or base functional groups. The perovskite crystallization kinetics are studied using in situ synchrotron‐based grazing‐incidence X‐ray scattering to explore the film formation mechanism. A model of the passivation mechanism is proposed to understand how the molecules simultaneously passivate the Pb–I antisite defects and vacancies created by under‐coordinated Pb atoms. In addition, it also explains how the energy offset between the semiconducting molecules and the perovskite influences trap states and intergrain carrier transport. The superior optoelectronic properties are attained by optimizing the molecular passivation treatments. These benefits are translated into significant enhancements of the power conversion efficiencies to 19.3%, as well as improved environmental and thermal stability of solar cells. The passivated devices without encapsulation degrade only by ≈13% after 40 d of exposure in 50% relative humidity at room temperature, and only ≈10% after 24 h at 80 °C in controlled environment.
Introducing semiconducting molecules with Lewis acid or base functional groups into a sol–gel MAPbI3 film promotes uniform decoration of grain boundaries within the bulk film. These molecules holistically passivate under‐coordinated Pb2+ vacancies or Pb–I antisite defects, leading to significant enhancements of the power conversion efficiency as well as improved environmental and thermal stability of solar cells.
Perovskite solar cells based on two-dimensional/three-dimensional (2D/3D) hierarchical structure have attracted significant attention in recent years due to their promising photovoltaic performance ...and stability. However, obtaining a detailed understanding of interfacial mechanism at the 2D/3D heterojunction, for example, the ligand-chemistry-dependent nature of the 2D/3D heterojunction and its influence on charge collection and the final photovoltaic outcome, is not yet fully developed. Here we demonstrate the underlying 3D phase templates growth of quantum wells (QWs) within a 2D capping layer, which is further influenced by the fluorination of spacers and compositional engineering in terms of thickness distribution and orientation. Better QW alignment and faster dynamics of charge transfer at the 2D/3D heterojunction result in higher charge mobility and lower charge recombination loss, largely explaining the significant improvements in charge collection and open-circuit voltage (V OC) in complete solar cells. As a result, 2D/3D solar cells with a power-conversion efficiency of 21.15% were achieved, significantly higher than the 3D counterpart (19.02%). This work provides key missing information on how interfacial engineering influences the desirable electronic properties of the 2D/3D hierarchical films and device performance via ligand chemistry and compositional engineering in the QW layer.
Organic–inorganic lead‐based halide perovskite compounds currently yield thin film solar cells with a power conversion efficiency (PCE) of >23%. However, replacing the lead with less‐toxic elements ...while maintaining a high PCE remains a challenge. For this reason, there has been significant effort to develop Pb‐free compounds, including methylammonium bismuth iodide (MA3Bi2I9), but such systems severely underperform when compared with the prototypical Pb‐based methylammonium lead iodide (MAPbI3). For the latter, it is known that lead complexes with polar solvents, such as dimethyl sulfoxide (DMSO) and dimethylformamide (DMF), to form iodoplumbates which can co‐crystallize into solvated phases. Herein, the solidification and growth behaviors of Bi‐ and Pb‐based films is investigated using multi‐probe in situ characterization methods. It is shown that the Bi‐based compound crystallizes directly and rapidly into a textured polycrystalline microstructure from a precursor solution without evolving through intermediate crystalline solvated phases, in contrast to MAPbI3. This solidification process produces isolated crystals and challenges the growth of continuous and crystalline films required for solar cells. It is revealed that solvent engineering with antisolvent dripping is crucial to enable the formation of continuous polycrystalline films of MA3Bi2I9 and functional solar cells thereof.
Formation of lead‐free methylammonium bismuth iodide (MA3Bi2I9) films is investigated in situ by X‐ray scattering and optical spectroscopy and contrasted to methylammonium lead iodide (MAPbI3). The Bi‐based compound crystallizes directly from solution, whereas the Pb‐based perovskite initially forms a solvated crystalline phase requiring annealing for conversion. Both materials benefit from anti‐solvent dripping while the as‐cast film is in the disordered sol–gel state.
Eco-friendly printing is important for mass manufacturing of thin-film photovoltaic (PV) devices to preserve human safety and the environment and to reduce energy consumption and capital expense. ...However, it is challenging for perovskite PVs due to the lack of eco-friendly solvents for ambient fast printing. In this study, we demonstrate for the first time an eco-friendly printing concept for high-performance perovskite solar cells. Both the perovskite and charge transport layers were fabricated from eco-friendly solvents
scalable fast blade coating under ambient conditions. The perovskite dynamic crystallization during blade coating investigated using
grazing incidence wide-angle X-ray scattering (GIWAXS) reveals a long sol-gel window prior to phase transformation and a strong interaction between the precursors and the eco-friendly solvents. The insights enable the achievement of high quality coatings for both the perovskite and charge transport layers by controlling film formation during scalable coating. The excellent optoelectronic properties of these coatings translate to a power conversion efficiency of 18.26% for eco-friendly printed solar cells, which is on par with the conventional devices fabricated
spin coating from toxic solvents under inert atmosphere. The eco-friendly printing paradigm presented in this work paves the way for future green and high-throughput fabrication on an industrial scale for perovskite PVs.
Perovskite photovoltaic solar cells have gained popularity throughout the past few years. They have become the subject of multiple research studies due to their ability to achieve high efficiencies, ...specifically all-inorganic perovskite solar cells. They demonstrate a record operational lifetime and are also cheap to manufacture and highly efficient. This paper intends to build on the existing knowledge and provide a detailed summary of how these perovskites work and the technology behind as well as the various fabrication methods. The review will also consider the production challenges while presenting upscaling alternatives to overcome them.
Ambient stability remains a critical hurdle for commercialization of perovskite solar cells. Two-dimensional Ruddlesden–Popper (RP) perovskite solar cells exhibit excellent stability but suffer from ...low photovoltaic performance so far. Herein, a RP/3D heterostructure passivated by semiconducting molecules is reported, which systematically addresses both charge dynamics and degradation mechanisms in concert for cesium-free FAPbI3 solar cells, delivering a power-conversion efficiency as high as 20.62% and remarkable long-term ambient stability with a t80 lifetime exceeding 2880 hours without encapsulation. In situ characterizations were carried out to gain insight into structural evolution and crystal growth mechanisms during spin coating. Comprehensive film and device characterizations were performed to understand the influences of the RP perovskite and molecule passivation on the film quality, photovoltaic performance and degradation mechanisms. This enables fabrication of a superior quality film with significantly improved optoelectronic properties, which lead to higher charge collection efficiency. The underlying mitigated degradation mechanisms of the passivated RP/3D devices were further elucidated. The understanding of the necessity of addressing both the charge dynamics and degradation mechanisms of solar cells will guide the future design and fabrication of chemically stable, high-efficiency photovoltaic devices.
Ambient stability remains a critical hurdle for commercialization of perovskite solar cells. Two-dimensional Ruddlesden–Popper (RP) perovskite solar cells exhibit excellent stability but suffer from ...low photovoltaic performance so far. Herein, a RP/3D heterostructure passivated by semiconducting molecules is reported, which systematically addresses both charge dynamics and degradation mechanisms in concert for cesium-free FAPbI 3 solar cells, delivering a power-conversion efficiency as high as 20.62% and remarkable long-term ambient stability with a t 80 lifetime exceeding 2880 hours without encapsulation. In situ characterizations were carried out to gain insight into structural evolution and crystal growth mechanisms during spin coating. Comprehensive film and device characterizations were performed to understand the influences of the RP perovskite and molecule passivation on the film quality, photovoltaic performance and degradation mechanisms. This enables fabrication of a superior quality film with significantly improved optoelectronic properties, which lead to higher charge collection efficiency. The underlying mitigated degradation mechanisms of the passivated RP/3D devices were further elucidated. The understanding of the necessity of addressing both the charge dynamics and degradation mechanisms of solar cells will guide the future design and fabrication of chemically stable, high-efficiency photovoltaic devices.
The two-dimensional (2D) perovskites stabilized by alternating cations in the interlayer space (ACI) define a new type of structure with different physical properties than the more common ...Ruddlesden–Popper counterparts. However, there is a lack of understanding of material crystallization in films and its influence on the morphological/optoelectronic properties and the final photovoltaic devices. Herein, we undertake in situ studies of the solidification process for ACI 2D perovskite (GA)(MA) n Pb n I3n+1 (⟨n⟩ = 3) from ink to solid-state semiconductor, using solvent mixture of DMSO:DMF (1:10 v/v) as the solvent and link this behavior to solar cell devices. The in situ grazing-incidence X-ray scattering (GIWAXS) analysis reveals a complex journey through disordered sol–gel precursors, intermediate phases, and ultimately to ACI perovskites. The intermediate phases, including a crystalline solvate compound and the 2D GA2PbI4 perovskite, provide a scaffold for the growth of the ACI perovskites during thermal annealing. We identify 2D GA2PbI4 to be the key intermediate phase, which is strongly influenced by the deposition technique and determines the formation of the 1D GAPbI3 byproducts and the distribution of various n phases of ACI perovskites in the final films. We also confirm the presence of internal charge transfer between different n phases through transient absorption spectroscopy. The high quality ACI perovskite films deposited from solvent mixture of DMSO:DMF (1:10 v/v) deliver a record power conversion efficiency of 14.7% in planar solar cells and significantly enhanced long-term stability of devices in contrast to the 3D MAPbI3 counterpart.
Perovskite solar cells increasingly feature mixed‐halide mixed‐cation compounds (FA1−x−yMAxCsyPbI3−zBrz) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the ...underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti‐solvent processing window for the fabrication of high‐quality films and efficient solar cells. This window widens from seconds, in the case of single cation/halide systems (e.g., MAPbI3, FAPbI3, and FAPbBr3), to several minutes for mixed systems. In situ X‐ray diffraction studies reveal that the processing window is closely related to the crystallization of the disordered sol–gel and to the number of crystalline byproducts; the processing window therefore depends directly on the precise cation/halide composition. Moreover, anti‐solvent dripping is shown to promote the desired perovskite phase with careful formulation. The processing window of perovskite solar cells, as defined by the latest time the anti‐solvent drip yields efficient solar cells, broadened with the increasing complexity of cation/halide content. This behavior is ascribed to kinetic stabilization of sol–gel state through cation/halide engineering. This provides guidelines for designing new formulations, aimed at formation of the perovskite phase, ultimately resulting in high‐efficiency perovskite solar cells produced with ease and with high reproducibility.
The role of cation and halide mixing is revealed using in situ X‐ray scattering measurements during spin‐coating. Modulating the cation/halide composition directly impacts the lifetime of the sol–gel precursor film and its easy and reproducible conversion to the perovskite phase to yield solar cells with 20% power conversion efficiency.
Mixed lead halide perovskite solar cells have been demonstrated to benefit tremendously from the addition of Cs+ and Rb+, but its root cause is yet to be understood. This hinders further improvement, ...and processing approaches remain largely empirical. We address the challenge by tracking the solidification of precursors in situ and linking the evolutions of different crystalline phases to the presence of Cs+ and Rb+. In their absence, the perovskite film is inherently unstable, segregating into MA-I- and FA-Br-rich phases. Adding either Cs+ or Rb+ is shown to alter the solidification process of the perovskite films. The optimal addition of both Cs+ and Rb+ drastically suppress phase segregation and promotes the spontaneous formation of the desired α phase. We propose that the synergistic effect is due to the collective benefits of Cs+ and Rb+ on the formation kinetics of the α phase and on the halide distribution throughout the film.
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•Reveal phase segregation in mixed-halide perovskite films via in situ observation•Cs+ and Rb+ additions dictate the crystallization pathways and solar cell performance•Direct formation of perovskite phase is beneficial in minimizing halide segregation
Having recognized the potential of hybrid organic-inorganic perovskites solar cells, in recent years the photovoltaic community has shifted its focus away from efficiency improvements to simplifying the processing and improving the stability of devices. In this work, we utilize in situ and time-resolved X-ray scattering to track various phase evolutions during the perovskite film solidification to link the microstructure to the composition. In particular, we unravel the crucial roles of Cs+ and Rb+ in promoting the in situ formation of the perovskite phase prior to thermal annealing, thus preventing segregation of halides and cations. Our study points to a significant new guideline for designing mixed-halide mixed-cation perovskites: the sol-gel formulation must possess the ability to convert directly into the targeted perovskite phase without transitioning through compositionally distinct intermediate phases in order to minimize halide segregation and yield-homogenized films.
Inherent phase segregation occurs during the pristine film crystallization, resulting in non-uniform halide and cation compositions, including MA-I-rich ordered solvates and FA-Br-rich 6H phase. Addition of Cs+ and Rb+ jointly conducts the perovskite orchestra: they synergistically promote the crystallization of a single 3C perovskite phase with excellent optoelectronic properties when used collectively but promote multiple competing phases when used alone or absent, resulting in halide segregation and deficient solar cell performance.
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