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In article number 1605290, Hao-Wu Lin and co-workers report efficient all-vacuum-deposited inorganic cesium lead halide perovskite solar cells of which the stoichiometric ratios of the precursors were carefully calibrated by ellipsometry. The incorporation of bromine was exploited to further enhance the device performance and stability. The results provide a paragon for the use of inorganic precursors en route to efficient vacuum-deposited perovskite devices.

2D photonic crystals (2D-PCs) are directly patterned into methylammonium lead iodide perovskite layers by thermal nanoimprint lithography (NIL) at moderate temperatures of only 100 °C, as described in article number 1605003 by Thomas Riedl and co-workers. The imprinted layers are significantly smoothened and surface defects are eliminated upon thermal imprint. 2D-PCs afford lasing with ultra-low lasing thresholds of 3.8 μJ/cm² at room temperature, which is indicative of excellent material quality of the perovskite after imprint.

Carrier transport in methylammonium lead iodide (MAPbI₃)-based hybrid organic–inorganic perovskites (HOIPs) is obscured by vacancy-mediated ion migration. Thus, the nature of migrating species (cation/anion) and their effect on electronic transport in MAPbI₃ has remained controversial. Temperature-dependent pulsed voltage–current measurements of MAPbI₃ thin films are performed under dark conditions, designed to decouple ion-migration/accumulation and electronic transport. Measurement conditions (electric-field history and scan rate) are shown to affect the electronic transport in MAPbI₃ thin films, through a mechanism involving ion migration and accumulation at the electrode interfaces. The presence of thermally activated processes with distinct activation energies (E_a) of 0.1 ± 0.001 and 0.41 ± 0.02 eV is established, and are assigned to electromigration of iodine vacancies and methylammonium vacancies, respectively. Analysis of activation energies obtained from electronic conduction versus capacitive discharge shows that the electromigration of these ionic species is responsible for the modification of interfacial electronic properties of MAPbI₃, and elaborates previously unaddressed issues of “fast” and “slow” ion migration. The results demonstrate that the intrinsic behavior of MAPbI₃ material is responsible for the hysteresis of the solar cells, but also have implications for other HOIP-based devices, such as memristors, detectors, and energy storage devices.

It is demonstrated that hybrid perovskite (MAPbI₃)-based M–S–M devices show I–V anomalies (hysteresis and field/scan rate dependent dynamic rectification) even under dark conditions. Using temperature-dependent pulsed current–voltage measurements, the origin of such I–V anomalies in migration and accumulation of two ionic species with different activation energies (0.1 and 0.41 eV) is established.

The first complete electrochemical fabrication of perovskite has been achieved for perovskite solar cells, as presented by Hong Liu, Wenzhong Shen, and co-workers in article number 1606156. The cover shows the three stages in the fabrication from top to bottom: before reaction, first step, and second step (where perovskite is formed). The rectangle in the middle stands for the substrate in different stages.

The highest efficiencies reported for perovskite solar cells so far have been obtained mainly with methylammonium and formamidinium mixed cations. Currently, high-quality mixed-cation perovskite thin films are normally made by use of antisolvent protocols. However, the widely used “antisolvent”-assisted fabrication route suffers from challenges such as poor device reproducibility, toxic and hazardous organic solvent, and incompatibility with scalable fabrication process. Here, a simple dual-source precursor approach is developed to fabricate high-quality and mirror-like mixed-cation perovskite thin films without involving additional antisolvent process. By integrating the perovskite films into the planar heterojunction solar cells, a power conversion efficiency of 20.15% is achieved with negligible current density–voltage hysteresis. A stabilized power output approaching 20% is obtained at the maximum power point. These results shed light on fabricating highly efficient perovskite solar cells via a simple process, and pave the way for solar cell fabrication via scalable methods in the near future.

A dual-source precursor approach is developed to fabricate a high-quality and mirror-like mixed-cation perovskite without involving additional antisolvent process. By integrating the perovskite films into the planar heterojunction solar cells, a power conversion efficiency of 20.15% is achieved with negligible hysteresis effect. A stabilized power output approaching 20% is obtained at the maximum power point.

A high lithium conductive MoS₂/Celgard composite separator is reported as efficient polysulfides barrier in Li–S batteries. Significantly, thanks to the high density of lithium ions on MoS₂ surface, this composite separator shows high lithium conductivity, fast lithium diffusion, and facile lithium transference. When used in Li–S batteries, the separator is proven to be highly efficient for depressing polysulfides shuttle, leading to high and long cycle stability. With 65% of sulfur loading, the device with MoS₂/Celgard separator delivers an initial capacity of 808 mAh g⁻¹ and a substantial capacity of 401 mAh g⁻¹ after 600 cycles, corresponding to only 0.083% of capacity decay per cycle that is comparable to the best reported result so far. In addition, the Coulombic efficiency remains more than 99.5% during all 600 cycles, disclosing an efficient ionic sieve preventing polysulfides migration to the anode while having negligible influence on Li⁺ ions transfer across the separator. The strategy demonstrated in this work will open the door toward developing efficient separators with flexible 2D materials beyond graphene for energy-storage devices.

A MoS₂/Celgard separator is demonstrated to greatly improve cycle stability and Coulombic efficiency when used as separator in Li–S batteries, due to the high lithium conductivity and the stacked structure, which not only acts as ion sieves to block polysulfides, but also provides free spaces to accommodate various polysulfide intermediates via physiochemical interaction.

Perovskite solar cells (PSCs) based on organic monovalent cation (methylammonium or formamidinium) have shown excellent optoelectronic properties with high efficiencies above 22%, threatening the status of silicon solar cells. However, critical issues of long-term stability have to be solved for commercialization. The severe weakness of the state-of-the-art PSCs against moisture originates mainly from the hygroscopic organic cations. Here, rubidium (Rb) is suggested as a promising candidate for an inorganic–organic mixed cation system to enhance moisture-tolerance and photovoltaic performances of formamidinium lead iodide (FAPbI₃). Partial incorporation of Rb in FAPbI₃ tunes the tolerance factor and stabilizes the photoactive perovskite structure. Phase conversion from hexagonal yellow FAPbI₃ to trigonal black FAPbI₃ becomes favored when Rb is introduced. The authors find that the absorbance and fluorescence lifetime of 5% Rb-incorporated FAPbI₃ (Rb_0.05FA_0.95PbI₃) are enhanced than bare FAPbI₃. Rb_0.05FA_0.95PbI₃-based PSCs exhibit a best power conversion efficiency of 17.16%, which is much higher than that of the FAPbI₃ device (13.56%). Moreover, it is demonstrated that the Rb_0.05FA_0.95PbI₃ film shows superior stability against high humidity (85%) and the full device made with the mixed perovskite exhibits remarkable long-term stability under ambient condition without encapsulation, retaining the high performance for 1000 h.

Partial substitution of inorganic rubidium cation (Rb⁺) for formamidinium lead iodide (FAPbI₃) perovskite suppresses nonperovskite phase formation and increases fluorescence lifetime. Introduction of the smaller monovalent cation in FAPbI₃ renders the perovskite more tolerant to high humidity. These lead to enhanced photovoltaic performances and long-term stability of perovskite solar cells based on Rb-mixed FAPbI₃.

The performance of organic semiconductors in optoelectronic devices depends on the functional properties of the individual molecules and their mutual orientations when they are in the solid state. The effect of H- and J-aggregation on the photophysical properties and photovoltaic behavior of four electronically identical but structurally different thiophene–pyridine–diketopyrrolopyrrole molecules is studied. By introducing and changing the position of two hexyl side chains on the two peripheral thiophene units of these molecules, their aggregation in thin films between H-type and J-type is effectively tuned, as evidenced from the characteristics of optical absorption, fluorescence, and excited state lifetime. The two derivatives that assemble into J-type aggregates exhibit a significantly enhanced photovoltaic performance, up to an order of magnitude, compared to the two molecules that form H-type aggregates. The reasons for this remarkably different behavior are discussed.

The aggregation behavior of electronically identical thiophene–pyridine–diketopyrrolopyrrole molecules is modulated by introducing and modifying the position of two hexyl side chains on the peripheral thiophene rings. Improved photovoltaic performance is achieved for those molecules assembling into J-type aggregates in contrast to those forming H-aggregates as a result of a faster charge generation and a reduced bimolecular recombination.

Colloidal-quantum-dot (CQD) photovoltaic devices are promising candidates for low-cost power sources owing to their low-temperature solution processability and bandgap tunability. A power conversion efficiency (PCE) of >10% is achieved for these devices; however, there are several remaining obstacles to their commercialization, including their high energy loss due to surface trap states and the complexity of the multiple-step CQD-layer-deposition process. Herein, high-efficiency photovoltaic devices prepared with CQD-ink using a phase-transfer-exchange (PTE) method are reported. Using CQD-ink, the fabrication of active layers by single-step coating and the suppression of surface trap states are achieved simultaneously. The CQD-ink photovoltaic devices achieve much higher PCEs (10.15% with a certified PCE of 9.61%) than the control devices (7.85%) owing to improved charge drift and diffusion. Notably, the CQD-ink devices show much lower energy loss than other reported high-efficiency CQD devices. This result reveals that the PTE method is an effective strategy for controlling trap states in CQDs.

A colloidal quantum dot (CQD)-ink is developed by phase-transfer exchange, enabling the fabrication of active layers by single-step coating to achieve a thick film. The CQD-ink exhibits low surface traps due to improvement of surface passivation. Thus, incorporating the CQD-ink into devices shows high efficiency and low voltage loss.

Organic–inorganic hybrid perovskite materials with mixed cations have demonstrated tremendous advances in photovoltaics recently, by showing a significant enhancement of power conversion efficiency and improved perovskite stability. Inspired by this development, this study presents the facile synthesis of mixed-cation perovskite nanocrystals based on FA_(1−x)Cs_xPbBr₃ (FA = CH(NH₂)₂). By detailed characterization of their morphological, optical, and physicochemical properties, it is found that the emission property of the perovskite, FA_(1−x)Cs_xPbBr₃, is significantly dependent on the substitution content of the Cs cations in the perovskite composition. These mixed-cation perovskites are employed as light emitters in light-emitting diodes (LEDs). With an optimized composition of FA_0.8Cs_0.2PbBr₃, the LEDs exhibit encouraging performance with a highest reported luminance of 55 005 cd m⁻² and a current efficiency of 10.09 cd A⁻¹. This work provides important instructions on the future compositional optimization of mixed-cation perovskite for obtaining high-performance LEDs. The authors believe this work is a new milestone in the development of bright and efficient perovskite LEDs.

Organic–inorganic hybrid perovskite nanocrystals with mixed cations demonstrate tremendous advances in light-emitting diodes. The physicochemical properties of synthesized perovskite nanocrystals are significantly dependent on the substitution content of the caesium cations in the perovskite composition. This work provides important instructions on the future compositional optimization of mixed-cation perovskite for obtaining high-performance light-emitting diodes.

A new fluorinated nonfullerene acceptor, ITIC-Th1, has been designed and synthesized by introducing fluorine (F) atoms onto the end-capping group 1,1-dicyanomethylene-3-indanone (IC). On the one hand, incorporation of F would improve intramolecular interaction, enhance the push–pull effect between the donor unit indacenodithieno[3,2-b]thiophene and the acceptor unit IC due to electron-withdrawing effect of F, and finally adjust energy levels and reduce bandgap, which is beneficial to light harvesting and enhancing short-circuit current density (J_SC). On the other hand, incorporation of F would improve intermolecular interactions through CF···S, CF···H, and CF···π noncovalent interactions and enhance electron mobility, which is beneficial to enhancing J_SC and fill factor. Indeed, the results show that fluorinated ITIC-Th1 exhibits redshifted absorption, smaller optical bandgap, and higher electron mobility than the nonfluorinated ITIC-Th. Furthermore, nonfullerene organic solar cells (OSCs) based on fluorinated ITIC-Th1 electron acceptor and a wide-bandgap polymer donor FTAZ based on benzodithiophene and benzotriazole exhibit power conversion efficiency (PCE) as high as 12.1%, significantly higher than that of nonfluorinated ITIC-Th (8.88%). The PCE of 12.1% is the highest in fullerene and nonfullerene-based single-junction binary-blend OSCs. Moreover, the OSCs based on FTAZ:ITIC-Th1 show much better efficiency and better stability than the control devices based on FTAZ:PC₇₁BM (PCE = 5.22%).

Single-junction binary-blend nonfullerene polymer solar cells based on fluorinated acceptor ITIC-Th1 afford power conversion efficiency of 12.1%, which is much higher than those of nonfluorinated ITIC-Th (8.88%) and PC₇₁BM (5.22%) counterparts under the same condition. Moreover, the nonfullerene devices exhibit better thermal stability than the fullerene devices.