JIALINGBO

Nature Energy, Published online: 08 April 2021; doi:10.1038/s41560-021-00802-z

A universal solution-processed bottom-up quasi-epitaxial growth of highly oriented α-FAPbI₃ perovskite film is achieved through the synergetic effect of methylammonium chloride and a large-organic cation. In situ GIWAXS visualizes the BA-related intermediate phase formation at the bottom, which serves as a guiding template for the bottom-up quasi-epitaxial growth in the subsequent annealing process.

Abstract

Epitaxial growth gives the highest-quality crystalline semiconductor thin films for optoelectronic devices. Here, a universal solution-processed bottom-up quasi-epitaxial growth of highly oriented α-formamidinium lead triiodide (α-FAPbI₃) perovskite film via a two-step method is reported, in which the crystal orientation of α-FAPbI₃ film is precisely controlled through the synergetic effect of methylammonium chloride and the large-organic cation butylammonium bromide. In situ GIWAXS visualizes the BA-related intermediate phase formation at the bottom of film, which serves as a guiding template for the bottom-up quasi-epitaxial growth in the subsequent annealing process. The template-guided epitaxially grown BAFAMA perovskite film exhibits increased crystallinity, preferred crystallographic orientation, and reduced defects. Moreover, the BAFAMA perovskite solar cells demonstrate decent stability, maintaining 95% of their initial power conversion efficiency after 2600 h ambient storage, and 4-time operation condition lifetime enhancement.

2D homochiral lead‐iodide perovskites were constructed by the introduction of a chiral center. The perovskites exhibit coexisting ferroelectricity, ferroelasticity, and reversible thermochromism, offering great application prospects for next‐generation smart devices.

Abstract

Chiral perovskites have emerged as a significant class of materials showing promising optoelectronic and spintronic applications. Reports of chiral perovskite ferroelectrics, however, have been scarce. In this work, we have successfully synthesized homochiral lead–iodide perovskite ferroelectrics [(R)‐N‐(1‐phenylethyl)ethane‐1,2‐diaminium]PbI₄ and [(S)‐N‐(1‐phenylethyl)ethane‐1,2‐diaminium]PbI₄ by introducing a methyl group into the organic cation of the parent (N‐benzylethane‐1,2‐diaminium)PbI₄. Vibrational circular dichroism spectra identify the chiral mirroring relationship. They both undergo 222F2‐type paraelectric–ferroelectric behavior at around 378 K coupled with clear ferroelastic domain “ON/OFF” switching. Besides, they exhibit an evident thermochromism with color change from orange–yellow to orange–red. To our knowledge, the discovery of integrated ferroelectricity, ferroelasticity, and reversible thermochromism in chiral perovskites is unprecedented.

Perovskite solar cells (PSCs) are considered as promising candidates for next-generation space photovoltaic technology. Key space environments and specific requirements for space photovoltaics are outlined. Some recent advances in terms of performance evolution and mechanism exploration of perovskite films and devices under space extreme environments are summarized. Progress and challenges associated with space applications of PSCs are highlighted.

Abstract

Metal halide perovskites have aroused burgeoning interest in the field of photovoltaics owing to their versatile optoelectronic properties. The outstanding power conversion efficiency, high specific power (i.e., power to weight ratio), compatibility with flexible substrates, and excellent radiation resistance of perovskite solar cells (PSCs) enable them to be a promising candidate for next-generation space photovoltaic technology. Nevertheless, compared with other practical space photovoltaics, such as silicon and III-V multi-junction compound solar cells, the research on PSCs for space applications is just in the infancy stage. Therefore, there are considerable interests in further strengthening relevant research from the perspective of both mechanism and technology. Consequently, the approaches used for and the consequences of PSCs for space applications are reviewed. This review provides an overview of recent progress in PSCs for space applications in terms of performance evolution and mechanism exploration of perovskite films and devices under space extreme environments.

In article number 2008091, Mingzhu Li, Wei E. I. Sha, Yanlin Song, and co‐workers design and fabricate colorful efficient perovskite solar cells (PSCs) incorporating moiré interference structures by imprinting with a commercial DVD disc. The light‐harvesting is boosted by elongation of the optical path and “folding” sunlight into the perovskite layer through changing the rotation angle. The moiré‐PSC with an optimized 30° rotation angle achieves an efficiency over 21.76%.

We developed a size effect that controls the crystallization of perovskite and enhances the passivation effect with g-C₃N₄ additive. The similarity in value of lattice constant and distance between double hydrogen binding sites affects crystallization. The combination allows g-C₃N₄ to cover tin-based perovskite, thus improves hydrophobicity and oxidation resistance of films and leads to splendid PCE of wearable device with excellent stability.

Abstract

Tin-based perovskite solar cells (PSCs) demonstrate a potential application in wearable electronics due to its hypotoxicity. However, poor crystal quality is still the bottleneck for achieving high-performance flexible devices. In this work, graphite phase-C₃N₄ (g-C₃N₄) is applied into tin-based perovskite as a crystalline template, which delays crystallization via a size-effect and passivates defects simultaneously. The double hydrogen bond between g-C₃N₄ and formamidine cation can optimize lattice matching and passivation. Moreover, the two-dimensional network structure of g-C₃N₄ can fit on the crystals, resulting an enhanced hydrophobicity and oxidation resistance. Therefore, the flexible tin-based PSCs with g-C₃N₄ realize a stabilized power conversion efficiency (PCE) of 8.56 % with negligible hysteresis. In addition, the PSCs can maintain 91 % of the initial PCE after 1000 h under N₂ environment and keep 92 % of their original PCE after 600 cycles at a curvature radius of 3 mm.

Perovskite Solar Cells

In article number 2000707, Enrique Hernández‐Balaguera and co‐workers explored the inherent characteristic phenomenology of perovskite solar cells, in terms of anomalous ionic and electronic dynamics, long‐memory effects, and anomalous hysteresis, using electrical analysis strategies and fractional calculus tools. Thus, this work can help to advance in the understanding of the key attributes and unique physical mechanisms of photovoltaic perovskites at long time scales.

Publication date: July 2021

Source: Nano Energy, Volume 85

Author(s): Jianxing Xia, Ruiling Zhang, Junsheng Luo, Hua Yang, Hongyu Shu, Haseeb Ashraf Malik, Zhongquan Wan, Yu Shi, Keli Han, Ruilin Wang, Xiaojun Yao, Chunyang Jia

In for the CIL: Highly stable inverted perovskite solar cells (PSCs) are assembled by using chemically modified titanium suboxide (TiO _x ) as the cathode interfacial layer (CIL). Codoping enhances the electrical properties of the TiO _x CIL, providing better inner encapsulation with thick film configuration. The PSCs exhibit significantly improved operational stability, maintaining >77 % of their initial efficiencies for up to 300 h without encapsulation.

Abstract

Achieving long-term device stability is one of the most challenging issues that impede the commercialization of perovskite solar cells (PSCs). Recent studies have emphasized the significant role of the cathode interfacial layer (CIL) in determining the stability of inverted p-i-n PSCs. However, experimental investigations focusing on the influence of the CIL on PSC degradation have not been systematically carried out to date. In this study, a comparative analysis was performed on the PSC device stability by using four different CILs including practical oxides like ZnO and TiO _x . A new implemented co-doping approach was found to results in high device performance and enhanced device stability. The PSC with a thick film configuration of chemically modified TiO _x CIL preserves over 77 % of its initial efficiencies of 17.24 % for 300 h under operational conditions without any encapsulation. The PSCs developed are among the most stable reported for methylammonium lead iodide (MAPbI₃) perovskite compositions.

The titanium diisopropoxide bis(acetylacetonate) molecules are incorporated into tin oxide (SnO₂) nanoparticle solution, in which the TiO₄ ^4– core, functional CO, and long alkene groups are used to tune the energy level, morphology, conductivity, and surface intimacy of the SnO₂ layer. As a result, the efficiency of perovskite solar cells is boosted from 18% to above 20% with significantly reduced hysteresis.

Abstract

Solution-processed tin oxide (SnO₂) is ubiquitously used as the electron transport layer (ETL) in perovskite solar cells, while the main concerns related to the application of SnO₂ nanoparticles are the self-aggregation potential and infeasible energy level adjustment, leading to inhomogeneous thin films and mismatched energy alignment with perovskite. Herein, a novel route is developed by adding a functional titanium diisopropoxide bis(acetylacetonate) (TiAcAc) molecule, comprising TiO₄ ^4– core, functional CO, and long alkene groups, into the SnO₂ nanoparticle solution, to optimize the electronic transfer property of SnO₂ for efficient perovskite solar cells. It is found that the TiO₄ ^4– can be used to tune the electronic property of the SnO₂ layer, and the long alkenes can act as a stabilizer to avoid the nanoparticle aggregation and electronic glue among the SnO₂ nanoparticles in the eventual nanoparticulate thin film, enhancing its homogeneity and conductivity. Furthermore, the residual CO groups on the ETL surface can strongly associate with the Pb²⁺ and improve the interface intimacy between the ETL and perovskite. As a result, the efficiency of perovskite solar cells can be boosted from 18% to above 20% with significantly reduced hysteresis by employing SnO₂-TiAcAc as electron transport layer, indicating a great potential for efficient perovskite solar cells.

Nature, Published online: 05 April 2021; doi:10.1038/s41586-021-03406-5

UV light and surface defects accelerate the degradation process of perovskite solar cells (PSCs). In their Communication on page 8673, Mingzhu Li, Yanlin Song, and co‐workers utilize the tautomerism of “sunscreen” molecules under UV light illumination to protect the PSC from degradation and enable molecular defect passivation, achieving high efficiency and long‐term UV stability of PSCs.

Reducing and mitigating non‐radiative recombination defects in perovskite materials are still crucial prerequisites for achieving high performance in light‐emitting applications. Ethoxylated trimethylolpropane triacrylate is introduced in antisolvent to passivate surface and bulk defects during the spinning process, and external quantum efficiency of quasi‐2D perovskite light‐emitting diodes as high as 22.49% is demonstrated.

Abstract

Perovskite light‐emitting diodes (PeLEDs) are considered as particularly attractive candidates for high‐quality lighting and displays, due to possessing the features of wide gamut and real color expression. However, most PeLEDs are made from polycrystalline perovskite films that contain a high concentration of defects, including point and extended imperfections. Reducing and mitigating non‐radiative recombination defects in perovskite materials are still crucial prerequisites for achieving high performance in light‐emitting applications. Here, ethoxylated trimethylolpropane triacrylate (ETPTA) is introduced as a functional additive dissolved in antisolvent to passivate surface and bulk defects during the spinning process. The ETPTA can effectively decrease the charge trapping states by passivation and/or suppression of defects. Eventually, the perovskite films that are sufficiently passivated by ETPTA make the devices achieve a maximum external quantum efficiency (EQE) of 22.49%. To our knowledge, these are the most efficient green PeLEDs up to now. In addition, a threefold increase in the T ₅₀ operational time of the devices was observed, compared to control samples. These findings provide a simple and effective strategy to make highly efficient perovskite polycrystalline films and their optoelectronics devices.

The work presents a detailed understanding of solution-processing-dependent quantum well growth and its impact on charge transport and photovoltaic performance for Dion–Jacobson perovskite. Faster solvent removal during film formation leads to a gradient distribution of the quantum wells and a preferential perpendicular orientation. The highest efficiency of 15.81% for aromatic spacer-based Dion–Jacobson perovskite solar cells is achieved.

Abstract

Dion–Jacobson (DJ) 2D hybrid perovskite semiconductors offer improved environmental stability and higher structural diversity in comparison with their 3D analogous. However, lacking of controlled perovskite crystallization makes it a challenge to achieve high charge transport for photovoltaic devices. Here, a detailed understanding of effects on film formation during different solution-casting processes for the DJ perovskite (PDMA)(MA) _{n −1}Pb _n I_{3 n +1} (<n> = 4, PDMA refers to 1,4-phenylenedimethanammonium) in the final film structure and photovoltaic outcomes is presented. Faster removal of solvent from solution via hot-casting or antisolvent dripping results in a more uniform thickness distribution of quantum wells. This eventually enhances carrier transport greatly along perpendicular direction and increases power conversion efficiencies. A high efficiency of 15.81% is achieved for the hot-casting devices, which is also the highest for aromatic spacer-based DJ perovskite solar cells. This work helps to better understand the control of film formation during solution-casting for high performance solar cells.

This work presents a comprehensive review on the current understanding, and apparent contradictions, of experimental observation, interpretation, and theoretical hypotheses presented in the state-of-the-art mixed dimensional 2D-3D perovskite literature and identifies promising future research directions for enhancing the stability and performance of such devices.

Abstract

Perovskite solar cells are a potential game changer for the photovoltaics industry, courtesy of their facile fabrication and high efficiency. Despite this, commercialization is being held back by poor stability. To become economically feasible for commercial production, perovskite solar cells must meet or exceed industry standards for operational lifetime and reliability. In this regard, mixed dimensional 2D-3D perovskite solar cells, incorporating long carbon-chain organic spacer cations, have shown promising results, with enhancement in both device efficiency and stability. Dimensional engineering of perovskite films requires a delicate balance of 2D and 3D perovskite composition to take advantage of the specific properties of each material phase. This review summarizes and assesses the current understanding, and apparent contradictions in the state-of-the-art mixed dimensional perovskite solar cell literature regarding the origin of stability and performance enhancement. By combining and comparing results from experimental and theoretical studies it is focused on how the perovskite composition, film formation methods, additive and solvent engineering influence efficiency and stability, and identify future research directions to further improve both key performance metrics.

A self-sufficient micrometer-level vacuum growth chamber is proposed for MAPbBr₃ microcrystals to effectively prevent water and oxygen, and to greatly improve the thermal and optical stability by the reduction of deep level trap states.

Abstract

Perovskite materials and their optoelectronic devices have attracted intensive attentions in recent years. However, it is difficult to further improve the performance of perovskite devices due to the poor stability and the intrinsic deep level trap states (DLTS), which are caused by surface dangling bonds and grain boundaries. Herein, the CH₃NH₃PbBr₃ perovskite microcrystal is encapsulated by a dense Al₂O₃ layer to form a microenvironment. Through optical measurement, it is found that the structure of perovskite can be healed by itself even under high temperature and long-time laser illumination. The DLTS density decreases nearly an order of magnitude, which results in 4–14 times enhancement of light emission. The observation is ascribed to the micron-level environment, which serves as a self-sufficient high-vacuum growth chamber, where the components of the perovskite are completely retained when sublimated and the decomposed atoms can re-arrange after thermal treatment. The modified structure showing high thermal stability is able to maintain excellent optical and lasing stability up to 2 years. This discovery provides a new idea and perspective for improving the stability of perovskite and can be of practical interest for perovskite device application.