Mahui

An efficient control of the film quality and thickness distribution of alternating cations in the interlayer space of 2D perovskite (GA)(MA) _n Pb _n I_{3 n +1} (〈n〉 = 3) quantum wells via incorporation of methylammonium chloride as an additive is demonstrated. The optimized device leads to more efficient charge transport and suppressed nonradiative charge recombination. Consequently, the optimized perovskite solar cell delivers an efficiency of 18.48%.

Abstract

2D perovskites stabilized by alternating cations in the interlayer space (ACI) represent a very new entry as highly efficient semiconductors for solar cells approaching 15% power conversion efficiency (PCE). However, further improvements will require understanding of the nature of the films, e.g., the thickness distribution and charge‐transfer characteristics of ACI quantum wells (QWs), which are currently unknown. Here, efficient control of the film quality of ACI 2D perovskite (GA)(MA) _n Pb _n I_{3 n +1} (〈n〉 = 3) QWs via incorporation of methylammonium chloride as an additive is demonstrated. The morphological and optoelectronic characterizations unambiguously demonstrate that the additive enables a larger grain size, a smoother surface, and a gradient distribution of QW thickness, which lead to enhanced photocurrent transport/extraction through efficient charge transfer between low‐n and high‐n QWs and suppressed nonradiative charge recombination. Therefore, the additive‐treated ACI perovskite film delivers a champion PCE of 18.48%, far higher than the pristine one (15.79%) due to significant improvements in open‐circuit voltage and fill factor. This PCE also stands as the highest value for all reported 2D perovskite solar cells based on the ACI, Ruddlesden–Popper, and Dion–Jacobson families. These findings establish the fundamental guidelines for the compositional control of 2D perovskites for efficient photovoltaics.

A new all‐inorganic perovskite material, CsPbI₃:Br:InI₃, is prepared through defect engineering of CsPbI₃. This new perovskite retains the same bandgap as CsPbI₃, but with intrinsic defect concentration largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere. By completely eliminating the labile and expensive components in traditional perovskite solar cells (PSCs), these all‐inorganic PSCs exhibit high photovoltaic performances.

Abstract

The emergence of cesium lead iodide (CsPbI₃) perovskite solar cells (PSCs) has generated enormous interest in the photovoltaic research community. However, in general they exhibit low power conversion efficiencies (PCEs) because of the existence of defects. A new all‐inorganic perovskite material, CsPbI₃:Br:InI₃, is prepared by defect engineering of CsPbI₃. This new perovskite retains the same bandgap as CsPbI₃, while the intrinsic defect concentration is largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere and thus a glovebox is not required. By completely eliminating the labile and expensive components in traditional PSCs, the all‐inorganic PSCs based on CsPbI₃:Br:InI₃ and carbon electrode exhibit PCE and open‐circuit voltage as high as 12.04% and 1.20 V, respectively. More importantly, they demonstrate excellent stability in air for more than two months, while those based on CsPbI₃ can survive only a few days in air. The progress reported represents a major leap for all‐inorganic PSCs and paves the way for their further exploration in order to achieve higher performance.

A novel and stable 2D Ruddlesden–Popper‐type layered chalcogenide perovskite semiconductor Ca₃Sn₂S₇, with graphene‐like linear electronic dispersion, small carrier effective mass (0.04 m₀), ultrahigh carrier mobility (6.7 × 10⁴ cm² V⁻¹ s⁻¹), Fermi velocity (3 × 10⁵ m s⁻¹), and optical absorption coefficient (10⁵ cm⁻¹), is found. Particularly, its direct quasi‐particle bandgap of 0.5 eV realizes the dream of opening the graphene bandgap in a new way.

Abstract

Graphene, a star 2D material, has attracted much attention because of its unique properties including linear electronic dispersion, massless carriers, and ultrahigh carrier mobility (10⁴–10⁵ cm² V⁻¹ s⁻¹). However, its zero bandgap greatly impedes its application in the semiconductor industry. Opening the zero bandgap has become an unresolved worldwide problem. Here, a novel and stable 2D Ruddlesden–Popper‐type layered chalcogenide perovskite semiconductor Ca₃Sn₂S₇ is found based on first‐principles GW calculations, which exhibits excellent electronic, optical, and transport properties, as well as soft and isotropic mechanical characteristics. Surprisingly, it has a graphene‐like linear electronic dispersion, small carrier effective mass (0.04 m₀), ultrahigh room‐temperature carrier mobility (6.7 × 10⁴ cm² V⁻¹ s⁻¹), Fermi velocity (3 × 10⁵ m s⁻¹), and optical absorption coefficient (10⁵ cm⁻¹). Particularly, it has a direct quasi‐particle bandgap of 0.5 eV, which realizes the dream of opening the graphene bandgap in a new way. These results guarantee its application in infrared optoelectronic and high‐speed electronic devices.

Ionic conduction in the perovskite oxide La_0.9Sr_0.1Ga_0.95Mg_0.05O_{3– δ} (LSGM) is found to be strongly correlated with crystal structure. A structural design with simultaneously large unit‐cell volume and octahedral rotations for fast ionic conduction is proposed and realized in LSGM superlattice thin films, where the ionic conductivity is tuned with structure alone by a factor of ≈2.5 at 600 °C.

Abstract

Solid‐oxide fuel/electrolyzer cells are limited by a dearth of electrolyte materials with low ohmic loss and an incomplete understanding of the structure–property relationships that would enable the rational design of better materials. Here, using epitaxial thin‐film growth, synchrotron radiation, impedance spectroscopy, and density‐functional theory, the impact of structural parameters (i.e., unit‐cell volume and octahedral rotations) on ionic conductivity is delineated in La_0.9Sr_0.1Ga_0.95Mg_0.05O_{3– δ} . As compared to the zero‐strain state, compressive strain reduces the unit‐cell volume while maintaining large octahedral rotations, resulting in a strong reduction of ionic conductivity, while tensile strain increases the unit‐cell volume while quenching octahedral rotations, resulting in a negligible effect on the ionic conductivity. Calculations reveal that larger unit‐cell volumes and octahedral rotations decrease migration barriers and create low‐energy migration pathways, respectively. The desired combination of large unit‐cell volume and octahedral rotations is normally contraindicated, but through the creation of superlattice structures both expanded unit‐cell volume and large octahedral rotations are experimentally realized, which result in an enhancement of the ionic conductivity. All told, the potential to tune ionic conductivity with structure alone by a factor of ≈2.5 at around 600 °C is observed, which sheds new light on the rational design of ion‐conducting perovskite electrolytes.

Combining the advantages of aggregation‐induced emission (AIE) and organic room‐temperature phosphorescence (RTP), as‐designed RTP‐AIEgens show a maximum photoluminescence quantum yield of 64%. Devices are then fabricated, and nondoped organic light‐emitting diodes (OLEDs) based on the RTP AIEgens exhibit relatively small efficiency roll‐off and efficient electroluminescence quantum efficiency, breaking the theoretical limit of conventional fluorescent OLEDs.

Abstract

Aggregation‐induced emission (AIE) is a beneficial strategy for generating highly effective solid‐state molecular luminescence without suffering losses in quantum yield. However, the majority of reported AIE‐active molecules exhibit only strong fluorescence, which is not ideal for electrical excitation in organic light‐emitting diodes (OLEDs). By introducing various substituent groups onto the biscarbazole compound, a series of molecular materials with aggregation‐induced phosphorescence (AIP) is designed, which exhibits two distinctly different phosphorescence bands and an absolute solid‐state room‐temperature phosphorescence quantum yield up to 64%. Taking advantage of the AIE feature, the AIP molecules are fabricated into OLEDs as a homogeneous light‐emitting layer, which allows for relatively small efficiency roll‐off and shows an external electroluminescence quantum yield of up to 5.8%, more than the theoretical limit for purely fluorescent OLED devices. The design showcases a promising strategy for the production of cost‐effective and highly efficient OLED technology.

The rapid development in large‐area organic solar cells (OSCs) is reviewed. Materials requirements, modular designs, and printing methods for large‐area OSCs are discussed. By combining thick‐film material systems with efficient modular designs, and then by employing the right printing methods, the fabrication of large‐area OSCs will be successfully realized in the near future.

Abstract

The printing of large‐area organic solar cells (OSCs) has become a frontier for organic electronics and is also regarded as a critical step in their industrial applications. With the rapid progress in the field of OSCs, the highest power conversion efficiency (PCE) for small‐area devices is approaching 15%, whereas the PCE for large‐area devices has also surpassed 10% in a single cell with an area of ≈1 cm². Here, the progress of this fast developing area is reviewed, mainly focusing on: 1) material requirements (materials that are able to form efficient thick active layer films for large‐area printing); 2) modular designs (effective designs that can suppress electrical, geometric, optical, and additional losses, leading to a reduction in the PCE of the devices, as a consequence of substrate area expansion); and 3) printing methods (various scalable fabrication techniques that are employed for large‐area fabrication, including knife coating, slot‐die coating, screen printing, inkjet printing, gravure printing, flexographic printing, pad printing, and brush coating). By combining thick‐film material systems with efficient modular designs exhibiting low‐efficiency losses and employing the right printing methods, the fabrication of large‐area OSCs will be successfully realized in the near future.

Thanks to the strong electron‐donating capability of carbon–oxygen‐bridged (CO‐bridged) ladder‐type building blocks, CO‐bridged nonfullerene acceptors (NFAs) present low bandgaps and strong light‐harvesting capability, delivering high short‐circuit current density (>28 mA cm⁻²) and high power conversion efficiency (>14% for single‐junction and >17% for tandem) in organic solar cells.

Abstract

Recently, acceptor–donor–acceptor (A–D–A) small molecules have emerged as promising nonfullerene acceptors (NFAs) for organic solar cells and have attracted great attention. The carbon‐bridged (C‐bridged) ladder‐type D unit plays a crucial role in developing high‐performance A–D–A NFAs. However, the medium electron‐donating capability of C‐bridged units is unfavorable for making NFAs with strong light‐harvesting capability. In this regard, carbon–oxygen‐bridged (CO‐bridged) ladder‐type units present advantages in developing strong light‐absorbing NFAs. Here, recent progress in the newly emerging CO‐bridged NFAs is highlighted. The synthetic methods for the polycyclic CO‐bridged building blocks are introduced. The photovoltaic performance for CO‐bridged NFAs is summarized and discussed. Perspectives on developing high‐performance CO‐bridged‐NFA‐based solar cells are made.

Aromatic‐diimide‐based polymers have emerged as the most promising n‐type semiconductors and their photovoltaic performance has been significantly improved in the past decade. The recent exciting progress is highlighted and the structure–property relationship of aromatic‐diimde‐based photovoltaic polymers is revealed, which could provide important guidelines for the further design of n‐type photovoltaic polymers.

Abstract

All‐polymer solar cells (all‐PSCs) have attracted immense attention in recent years due to their advantages of tunable absorption spectra and electronic energy levels for both donor and acceptor polymers, as well as their superior thermal and mechanical stability. The exploration of the novel n‐type conjugated polymers (CPs), especially based on aromatic diimide (ADI), plays a vital role in the further improvement of power conversion efficiency (PCE) of all‐PSCs. Here, recent progress in structure modification of ADIs including naphthalene diimide (NDI), perylene diimide (PDI), and corresponding derivatives is reviewed, and the structure–property relationships of ADI‐based CPs are revealed.

Interfaces between the photoactive layer and electrodes play a critical role in ultimate device behaviors in organic bulk heterojunction solar cells (OSCs) and hybrid halide perovskite solar cells (PSCs). Recent progress in interface modification for OSCs and PSCs aimed at improving interfacial charge extraction and mitigating surface recombination, and at enhancing trap passivation and device stability is presented.

Abstract

Organic bulk heterojunction solar cells (OSCs) and hybrid halide perovskite solar cells (PSCs) are two promising photovoltaic techniques for next‐generation energy conversion devices. The rapid increase in the power conversion efficiency (PCE) in OSCs and PSCs has profited from synergetic progresses in rational material synthesis for photoactive layers, device processing, and interface engineering. Interface properties in these two types of devices play a critical role in dictating the processes of charge extraction, surface trap passivation, and interfacial recombination. Therefore, there have been great efforts directed to improving the solar cell performance and device stability in terms of interface modification. Here, recent progress in interfacial doping with biopolymers and ionic salts to modulate the cathode interface properties in OSCs is reviewed. For the anode interface modification, recent strategies of improving the surface properties in widely used PEDOT:PSS for narrowband OSCs or replacing it by novel organic conjugated materials will be touched upon. Several recent approaches are also in focus to deal with interfacial traps and surface passivation in emerging PSCs. Finally, the current challenges and possible directions for the efforts toward further boosts of PCEs and stability via interface engineering are discussed.

Organic–inorganic metal halide perovskites have been emerging as one of the most powerful optoelectronic materials. In article number https://doi.org/10.1002/adma.2019040731904073, Ji Tae Kim and co‐workers develop a nanoscale 3D‐printing method for organic–inorganic metal halide perovskites. The method, which exploits a femtoliter ink meniscus to guide crystallization, offers a high degree of control over the printed shapes and positions in three‐dimensions. The new manufacturing route developed here provides insight into the next‐generation of 3D‐printed optoelectronic devices.

An electron‐deficient unit containing B←N bonds, namely BNIDT, is developed to construct polymer acceptors for photovoltaic applications. Desirable optoelectronic properties such as broad absorption profiles, low‐lying energy levels, ambipolar charge transport properties, and strong electron‐affinity are found for these polymers. All‐polymer solar cells using these B←N embedded polymers as acceptor materials exhibit an enhanced efficiency of 8.78%.

Abstract

In the field of all‐polymer solar cells (all‐PSCs), all efficient polymer acceptors that exhibit efficiencies beyond 8% are based on either imide or dicyanoethylene. To boost the development of this promising solar cell type, creating novel electron‐deficient units to build high‐performance polymer acceptors is critical. A novel electron‐deficient unit containing B←N bonds, namely, BNIDT, is synthesized. Systematic investigation of BNIDT reveals desirable properties including good coplanarity, favorable single‐crystal structure, narrowed bandgap and downshifted energy levels, and extended absorption profiles. By copolymerizing BNIDT with thiophene and 3,4‐difluorothiophene, two novel conjugated polymers named BN‐T and BN‐2fT are developed, respectively. It is shown that these polymers possess wide absorption spectra covering 350–800 nm, low‐lying energy levels, and ambipolar film‐transistor characteristics. Using PBDB‐T as the donor and BN‐2fT as the acceptor, all‐PSCs afford an encouraging efficiency of 8.78%, which is the highest for all‐PSCs excluding the devices based on imide and dicyanoethylene‐type acceptors. Considering that the structure of BNIDT is totally different from these classical units, this work opens up a new class of electron‐deficient unit for constructing efficient polymer acceptors that can realize efficiencies beyond 8% for the first time.

The hot‐pressing fabrication method for quasi‐monocrystalline CsPbBr₃ thick film and the performance of their X‐ray detection are introduced. The high crystalline quality of CsPbBr₃ films and the formation of self‐formed shallow bromide vacancy defects during the high‐temperature process result in a large µτ product and therefore high photoconductivity gain factor and record‐high detection sensitivity.

Abstract

An X‐ray detector with high sensitivity would be able to increase the generated signal and reduce the dose rate; thus, this type of detector is beneficial for applications such as medical imaging and product inspection. The inorganic lead halide perovskite CsPbBr₃ possesses relatively larger density and a higher atomic number in contrast to its hybrid counterpart. Therefore, it is expected to provide high detection sensitivity for X‐rays; however, it has rarely been studied as a direct X‐ray detector. Here, a hot‐pressing method is employed to fabricate thick quasi‐monocrystalline CsPbBr₃ films, and a record sensitivity of 55 684 µC Gy_air ⁻¹ cm⁻² is achieved, surpassing all other X‐ray detectors (direct and indirect). The hot‐pressing method is simple and produces thick quasi‐monocrystalline CsPbBr₃ films with uniform orientations. The high crystalline quality of the CsPbBr₃ films and the formation of self‐formed shallow bromide vacancy defects during the high‐temperature process result in a large µτ product and, therefore, a high photoconductivity gain factor and high detection sensitivity. The detectors also exhibit relatively fast response speed, negligible baseline drift, and good stability, making a CsPbBr₃ X‐ray detector extremely competitive for high‐contrast X‐ray detections.

A quasi‐two‐dimensional perovskite film with stable domain distribution is prepared based on a new spacer. The film containing pure bromide perovskite exhibits enhanced deep‐blue fluorescence with quantum yield of 77% by low‐dimensional component engineering. As a result, the corresponding light‐emitting diodes deliver stable deep‐blue emission with a peak external quantum efficiency of 2.6%.

Abstract

Compared to efficient green and near‐infrared light‐emitting diodes (LEDs), less progress has been made on deep‐blue perovskite LEDs. They suffer from inefficient domain [various number of PbX₆ ⁻ layers (n)] control, resulting in a series of unfavorable issues such as unstable color, multipeak profile, and poor fluorescence yield. Here, a strategy involving a delicate spacer modulation for quasi‐2D perovskite films via an introduction of aromatic polyamine molecules into the perovskite precursor is reported. With low‐dimensional component engineering, the n₁ domain, which shows nonradiative recombination and retarded exciton transfer, is significantly suppressed. Also, the n₃ domain, which represents the population of emission species, is remarkably increased. The optimized quasi‐2D perovskite film presents blue emission from the n₃ domain (peak at 465 nm) with a photoluminescence quantum yield (PLQY) as high as 77%. It enables the corresponding perovskite LEDs to deliver stable deep‐blue emission (CIE (0.145, 0.05)) with an external quantum efficiency (EQE) of 2.6%. The findings in this work provide further understanding on the structural and emission properties of quasi‐2D perovskites, which pave a new route to design deep‐blue‐emissive perovskite materials.

An efficient control of the film quality and thickness distribution of alternating cations in the interlayer space of 2D perovskite (GA)(MA) _n Pb _n I_{3 n +1} (〈n〉 = 3) quantum wells via incorporation of methylammonium chloride as an additive is demonstrated. The optimized device leads to more efficient charge transport and suppressed nonradiative charge recombination. Consequently, the optimized perovskite solar cell delivers an efficiency of 18.48%.

Abstract

2D perovskites stabilized by alternating cations in the interlayer space (ACI) represent a very new entry as highly efficient semiconductors for solar cells approaching 15% power conversion efficiency (PCE). However, further improvements will require understanding of the nature of the films, e.g., the thickness distribution and charge‐transfer characteristics of ACI quantum wells (QWs), which are currently unknown. Here, efficient control of the film quality of ACI 2D perovskite (GA)(MA) _n Pb _n I_{3 n +1} (〈n〉 = 3) QWs via incorporation of methylammonium chloride as an additive is demonstrated. The morphological and optoelectronic characterizations unambiguously demonstrate that the additive enables a larger grain size, a smoother surface, and a gradient distribution of QW thickness, which lead to enhanced photocurrent transport/extraction through efficient charge transfer between low‐n and high‐n QWs and suppressed nonradiative charge recombination. Therefore, the additive‐treated ACI perovskite film delivers a champion PCE of 18.48%, far higher than the pristine one (15.79%) due to significant improvements in open‐circuit voltage and fill factor. This PCE also stands as the highest value for all reported 2D perovskite solar cells based on the ACI, Ruddlesden–Popper, and Dion–Jacobson families. These findings establish the fundamental guidelines for the compositional control of 2D perovskites for efficient photovoltaics.

A new all‐inorganic perovskite material, CsPbI₃:Br:InI₃, is prepared through defect engineering of CsPbI₃. This new perovskite retains the same bandgap as CsPbI₃, but with intrinsic defect concentration largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere. By completely eliminating the labile and expensive components in traditional perovskite solar cells (PSCs), these all‐inorganic PSCs exhibit high photovoltaic performances.

Abstract

The emergence of cesium lead iodide (CsPbI₃) perovskite solar cells (PSCs) has generated enormous interest in the photovoltaic research community. However, in general they exhibit low power conversion efficiencies (PCEs) because of the existence of defects. A new all‐inorganic perovskite material, CsPbI₃:Br:InI₃, is prepared by defect engineering of CsPbI₃. This new perovskite retains the same bandgap as CsPbI₃, while the intrinsic defect concentration is largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere and thus a glovebox is not required. By completely eliminating the labile and expensive components in traditional PSCs, the all‐inorganic PSCs based on CsPbI₃:Br:InI₃ and carbon electrode exhibit PCE and open‐circuit voltage as high as 12.04% and 1.20 V, respectively. More importantly, they demonstrate excellent stability in air for more than two months, while those based on CsPbI₃ can survive only a few days in air. The progress reported represents a major leap for all‐inorganic PSCs and paves the way for their further exploration in order to achieve higher performance.

A novel and stable 2D Ruddlesden–Popper‐type layered chalcogenide perovskite semiconductor Ca₃Sn₂S₇, with graphene‐like linear electronic dispersion, small carrier effective mass (0.04 m₀), ultrahigh carrier mobility (6.7 × 10⁴ cm² V⁻¹ s⁻¹), Fermi velocity (3 × 10⁵ m s⁻¹), and optical absorption coefficient (10⁵ cm⁻¹), is found. Particularly, its direct quasi‐particle bandgap of 0.5 eV realizes the dream of opening the graphene bandgap in a new way.

Abstract

Graphene, a star 2D material, has attracted much attention because of its unique properties including linear electronic dispersion, massless carriers, and ultrahigh carrier mobility (10⁴–10⁵ cm² V⁻¹ s⁻¹). However, its zero bandgap greatly impedes its application in the semiconductor industry. Opening the zero bandgap has become an unresolved worldwide problem. Here, a novel and stable 2D Ruddlesden–Popper‐type layered chalcogenide perovskite semiconductor Ca₃Sn₂S₇ is found based on first‐principles GW calculations, which exhibits excellent electronic, optical, and transport properties, as well as soft and isotropic mechanical characteristics. Surprisingly, it has a graphene‐like linear electronic dispersion, small carrier effective mass (0.04 m₀), ultrahigh room‐temperature carrier mobility (6.7 × 10⁴ cm² V⁻¹ s⁻¹), Fermi velocity (3 × 10⁵ m s⁻¹), and optical absorption coefficient (10⁵ cm⁻¹). Particularly, it has a direct quasi‐particle bandgap of 0.5 eV, which realizes the dream of opening the graphene bandgap in a new way. These results guarantee its application in infrared optoelectronic and high‐speed electronic devices.

An ideal materials combination based on the electron donor BSFTR and acceptor Y6 is selected to construct small‐molecule solar cells (SMSCs). By morphology optimization, an extraordinary power conversion efficiency of 13.69% with a remarkably low energy loss of 0.48 eV is achieved, which is beneficial from the matched photoelectric properties, the favorable blend morphology, and is the best binary SMSC performance reported so far.

Abstract

Compared with the quick development of polymer solar cells, achieving high‐efficiency small‐molecule solar cells (SMSCs) remains highly challenging, as they are limited by the lack of matched materials and morphology control to a great extent. Herein, two small molecules, BSFTR and Y6, which possess broad as well as matched absorption and energy levels, are applied in SMSCs. Morphology optimization with sequential solvent vapor and thermal annealing makes their blend films show proper crystallinity, balanced and high mobilities, and favorable phase separation, which is conducive for exciton dissociation, charge transport, and extraction. These contribute to a remarkable power conversion efficiency up to 13.69% with an open‐circuit voltage of 0.85 V, a high short‐circuit current of 23.16 mA cm⁻² and a fill factor of 69.66%, which is the highest value among binary SMSCs ever reported. This result indicates that a combination of materials with matched photoelectric properties and subtle morphology control is the inevitable route to high‐performance SMSCs.

Herein, the dipolar polarization in a quasi‐2D organic–inorganic hybrid‐perovskite nanorod network–based solar cell using impedance spectroscopy is studied. Electric field and photoinduced dipole–dipole interaction plays an important role for the solar cell working at steady states.

Layered quasi‐2D organic–inorganic hybrid perovskites (OIHPs) prevent oxygen and moisture permeation, for long‐lifetime photovoltaic performance. Unfortunately, the electrical and photoinduced surface and dipolar polarizations caused due to the presence of the organic cation spacer in the structure remain unclear. Herein, a high‐performance planar quasi‐2D OIHP solar cell comprising (PEA)₂(MA)₃Pb₄I₁₃ (n = 4) is designed. It displays a large area coverage and an interconnected nanorod network, which contributes to efficient light absorption and charge carrier transport. The surface and dipolar polarizations exhibit remarkable light intensity and electric field–dependent characteristics at short‐circuit‐current (J _sc) and steady‐state (i.e., V _oc) conditions. More importantly, Voc exhibits a nonlinear behavior at steady states. Such a unique feature is in accordance with the dipolar polarization measured at the same condition. The phenomenon can be explained by the significant dipole–dipole interaction at lower electric field strengths. At higher field strengths, the screen of the dipoles due to charge accumulation at the surface of the organic cation spacer leads to slower increment of Voc. Thus, carefully designing the quasi‐2D perovskite nanostructure, together with the dielectric property of the organic cation spacer, may play an exceptionally important role for future high‐performance quasi‐2D perovskite solar cells.

Solution‐processed α‐In₂Se₃ is first used as the hole transport layer in polymer solar cells (PSCs) due to its significant photoelectric properties. A high power conversion efficiency of 9.58% is achieved in α‐In₂Se₃‐based devices, which is comparable with that of poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐based devices. Furthermore, the α‐In₂Se₃ film possesses excellent thermal stability and enhances the long‐term stability of PSCs.

Herein, a 2D α‐In₂Se₃ nanosheet, a binary III–VI group compound semiconductor, is fabricated by liquid‐phase exfoliation method, and the photoelectric properties of α‐In₂Se₃ material are investigated in depth. It is found that α‐In₂Se₃ film exhibits significant conductivity, outstanding optical transmission, and a suitable work function. Combined with its smooth surface and preferable hydrophobicity, α‐In₂Se₃ film can efficiently facilitate hole transporting in the polymer solar cells (PSCs). Due to the aforesaid advantages, a 2D α‐In₂Se₃ nanosheet is used as a hole transport layer (HTL) in conventional PSCs for the first time, and a relatively high power conversion efficiency (PCE) of 9.58% is achieved with the structure of ITO/α‐In₂Se₃/PBDB‐T:ITIC/Ca/Al, which is comparable with poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐based devices (9.50%). Interestingly, it is demonstrated that the α‐In₂Se₃ film possesses excellent thermal stability in the range from room temperature to 280 °C, and a PCE of 9.35% is achieved without annealing treatment of α‐In₂Se₃ film, which exhibits a great potential of α‐In₂Se₃ for an annealing‐free approach. Furthermore, the incorporation of α‐In₂Se₃ HTL also remarkably enhances the long‐term stability of PSCs compared with PEDOT:PSS‐based devices. So, the results show that 2D α‐In₂Se₃ is a promising candidate to be an efficient and stable hole‐extraction layer.

The different electron acceptors sensitizers ZL003 and ZL005 are rationally designed and applied in dye‐sensitized solar cells (DSSCs). The photoelectrochemical performance of ZL003 indicates that the rigid electron acceptor has a higher electron‐injection efficiency and considerable effect on the overall device efficiency through the time‐resolved photoluminescence (TR‐PL) spectroscopy.

High electron‐injection efficiency is important for further development of dye‐sensitized solar cells (DSSCs). Different electron acceptors have different electron‐injection capabilities, which affect device performance. Herein, the effects of two organic triazatruxene (TAT)‐based donor‐π‐bridge‐acceptor sensitizers applied in DSSCs are reported. The sensitizers have either rigid 4‐ethynyl benzoic acid (EBA) or Z‐type cyanoacrylic acid (CA) as their electron acceptor, denoted as ZL003 and ZL005, respectively. Time‐resolved photoluminescence (TR‐PL) spectroscopy is applied to reveal the electron transfer dynamics between the sensitizers and TiO₂ films. Notably, ZL003 has higher electron‐injection efficiency compared with that of ZL005, which is consistent with the higher efficiency and photocurrent of devices based on the former. The dye loading of ZL003 is nearly twice as great as that of ZL005, which accounts for the lower photocurrent of the device. The charge recombination lifetimes for the two dyes are consistent with their open‐circuit voltage. Consequently, the ZL003‐based devices achieve a higher power conversion efficiency of 13.4% compared with only 7.2% for ZL005.

A mixed antisolvent treatment by spraying acetonitrile (ACN)‐added chlorobenzene (CBZ) for the fabrication of high‐quality perovskite films is reported. It is found that while the lower‐boiling‐point ACN preserves the morphology of the perovskite film, it has a significant impact on perovskite crystallization dynamics. Moreover, the method developed herein is scalable for future large‐area devices.

Herein, a mixed anti‐solvent treatment by spraying acetonitrile (ACN)‐added chlorobenzene (CBZ) for the fabrication of high‐quality perovskite films is proposed. While the lower‐boiling‐point ACN preserves the morphology of the perovskite film, it has a significant impact on perovskite crystallization dynamics. While CBZ is responsible for facilitating nucleation, ACN performs two functions. ACN as a weak polarity solvent allows the organic salt in the perovskite complex to be redissolved for perovskite formation and loosens the dimethyl sulfoxide (DMSO)–PbI₂ bond for more rapid perovskite crystallization. For the mixed anti‐solvent treatment to be successful, an appropriate amount of ACN is the key and the use of spraying to dispense the mixed anti‐solvent is crucial. This is due to the more instant and rapid reaction caused by the ACN which is faster than spreading the ACN across the substrate by the spinning motion. The resultant film using an appropriate mixed anti‐solvent treatment is a pinhole‐free high‐quality perovskite film with larger grain and enhanced crystallinity compared with CBZ‐only treatment film. The best solar cell using this mixed anti‐solvent treatment with 20% of ACN and 80% of CBZ achieves a PCE of 20.1% due to the reduced recombination.

Solution‐processed MoO₃ (SM), synthesized by a simple low‐temperature process, is utilized as an efficient and stable anode interfacial layer for organic solar cells (OSCs). The ultrasmooth SM film, without pinholes, exhibits excellent photovoltaic performance and device stability in OSCs, maintaining ≈92% of its initial solar cell efficiency over 2500 h storage in inert conditions.

The interfacial layer (IL) in organic solar cells (OSCs) can be an important boosting factor for improving device efficiency and stability. Herein, a facile and cost‐effective approach to form a uniform molybdenum oxide (MoO₃) film with desirable stability is provided, based on solution processing at low temperatures by simplified precursor solution synthesis. The solution‐processed MoO₃ (SM) film, with oxygen vacancies induced by the hydroxyl group, functions as an efficient anode IL in conventional OSCs. The hole‐transporting performance of SM is well demonstrated in nonfullerene‐based OSCs exhibiting over 10% of power conversion efficiency. The enhanced device performance of SM‐based OSCs over that of poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is investigated by analyzing the morphology, electronic state, and electrical conductivity of such a hole‐transporting layer, as well as the charge dynamics in the completed devices. Furthermore, the high stability of the SM films in OSCs is examined under various environmental conditions, including long‐term and thermal stability. In particular, fullerene‐based OSCs with SM maintain over 90% of their initial cell performance over 2500 h under inert conditions. It is shown that solution‐processed metal oxides can be viable ILs with high functionality and versatility, overcoming the drawbacks of conventionally adopted conducting polymer interlayers.

Based on mixed halide perovskites, a pure blue film with a photoluminescence quantum yield of 88% is obtained. Corresponding blue perovskite light‐emitting diode (LED) exhibits electroluminescence (EL) at 468 nm with an external quantum efficiency of 0.71%. By introducing the square‐wave alternate voltage for driving LED device, the EL spectrum of the device shows negligible shifts for 12 h.

Abstract

Perovskite light‐emitting diodes (PeLEDs) have attracted great research interests considering their excellent luminescent properties and solution processability. Despite rapid advances of green‐, red‐, and near‐infrared‐emitting PeLEDs, blue‐PeLEDs, as an essential part for full‐color display and solid‐state lighting, still remain challenging due to their low efficiency and spectral instability. Here, reported are spectrally stable blue‐PeLEDs biased by an alternating voltage. First, 2‐phenoxyethylamine‐passivated CsPbBr _x Cl_{3− x} is obtained as a blue emitter with a record photoluminescence quantum yield of 88%. Subsequently, constructed and optimized are pure blue‐emitting PeLEDs exhibiting electroluminescence (EL) at 468 nm with a high external quantum efficiency of 0.71%. Furthermore, driven are the devices by square‐wave alternating voltage and stabilized are the EL spectra for 12 h by suppressing the detrimental halide migration during operation. It is believed that this work provides an alternative way for the spectrally stable mixed halide blue PeLEDs.

Over 2500 h operation lifetime at a high brightness of 1000 cd m⁻² light‐emitting diodes with high peak external quantum efficiency of 23.9%, current efficiency of 100.5 cd A⁻¹, and low efficiency roll‐off at high currents based on compositional graded ZnCdSe/ZnSe/ZnSeS/ZnS quantum dots are synthesized by a shell tailored strategy.

Abstract

Quantum dot light‐emitting diodes (QLEDs) are considered to be the candidate light sources with the most potential for applications in displays. Recent advances in luminance, external quantum efficiency (EQE), and even the operation lifetime of QLEDs have already satisfied the requirements for low‐light‐level displays. However, the short operation lifetime under high brightness limits the application of QLEDs for outdoor displays and lightings. Here, demonstrated are green QLEDs with a T ₉₅ operation lifetime reaching up to 2500 h at high brightness (1000 cd m⁻²) with a high peak EQE of 23.9%, current efficiency of 100.5 cd A⁻¹, and low efficiency roll‐off at high current. Both the EQE and lifetime of the QLEDs are superior to those reported to date for all solution‐processed green QLEDs. These major advances are qualitatively attributed to the use of a shell‐tailoring strategy for producing compositional graded CdZnSe/ZnSe/ZnSeS/ZnS quantum dots with a high photoluminescence quantum yield, suppressed nonradiative Förster resonant energy transfer and Auger recombination, and favorable valence band alignment for enhanced hole injection. Collectively, this work represents a huge step forward in eventually realizing QLEDs for high‐brightness display and lighting applications.

A very high‐efficiency host material for blue single‐layer phosphorescent organic light‐emitting diode (OLED) (external quantum efficiency reaching 17.6%) is reported. This host is synthesized via an efficient approach, displays a high E _T, adequate highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels, and suitable balance between hole and electron mobilities displaying all the required properties for reaching high‐performance single‐layer phosphorescent OLED.

Abstract

Herein, a high‐efficiency host material for single‐layer phosphorescent organic light‐emitting diodes (SL‐PhOLEDs) is reported. This host material is synthesized via an efficient approach and is constructed on the association of an electron‐rich phenylacridine unit connected by a spiro carbon atom to an electron‐deficient 2,7‐bis(diphenylphosphineoxide)‐fluorene. In addition to a high E _T value and adequate highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels, the key point in this molecular design is the suitable balance between hole and electron mobilities, which leads to a high‐performance blue SL‐PhOLED with an external quantum efficiency of 17.6% (current efficiency = 37.8 cd A⁻¹ and power efficiency = 37.1 lm W⁻¹) and a low V _on of 2.5 V. This performance shows that the molecular design of the present host fulfills the criteria required for high‐efficiency SL‐PhOLEDs. The present performance is one of the highest reported to date for blue SL‐PhOLEDs and more importantly shows the potential of such a molecular design to reach very high‐performance single‐layer devices.

Optically pumped lasing is demonstrated in distributed feedback hybrid perovskite light emitting diodes fabricated on both glass and Si substrates. Thresholds as low as ≈6 µJ cm⁻² at room temperature are achieved and retained under ≈2 A cm⁻² of pulsed electrical excitation.

Abstract

Electrically pumped lasing from hybrid organic–inorganic metal‐halide perovskite semiconductors could lead to nonepitaxial diode lasers that are tunable throughout the visible and near‐infrared spectrum; however, a viable laser diode architecture has not been demonstrated to date. Here, an important step toward this goal is achieved by demonstrating two distinct distributed feedback light‐emitting diode architectures that achieve low threshold, optically pumped lasing. Bottom‐ and top‐emitting perovskite light‐emitting diodes are fabricated on glass and Si substrates, respectively, using a polydimethylsiloxane stamp in the latter case to nanoimprint a second‐order distributed feedback grating directly into the methylammonium lead iodide active layer. The devices exhibit room temperature thresholds as low as ≈6 µJ cm⁻², a peak external quantum efficiency of ≈0.1%, and a maximum current density of ≈2 A cm⁻² that is presently limited by degradation associated with excessive leakage current. In this low current regime, electrical injection does not adversely affect the optical pump threshold, leading to a projected threshold current density of ≈2 kA cm⁻². Operation at low temperature can significantly decrease this threshold, but must overcome extrinsic carrier freeze‐out in the doped organic transport layers to maintain a reasonable drive voltage.

Here, a 3.19%‐external quantum efficiency all‐solution‐processed green perovskite light‐emitting diode is reported by employing 1,3,5‐tris(1‐phenyl‐1H‐benzimidazol‐2‐yl)benzene (TPBi) doped conjugated amino‐alkyl substituted polyfluorene poly[(9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] (PFN) as electron injection layer. The doping of TPBi into PFN not only enhances the capability of electron injection, but also significantly suppresses the emission quenching of perovskite caused by the charge transfer between perovskite and PFN.

Abstract

Metal halide perovskites have attracted considerable attention in the field of light‐emitting diodes due to their high color purity and solution processability. However, most perovskite light‐emitting diodes (PeLEDs) employ thermally deposited charge transport layers (CTLs) on top of perovskite layers. In order to realize low‐cost and scalable fabrication of PeLEDs, all‐solution process is highly desired, but still remaining great challenges. Here, an efficient all‐solution‐processed green PeLEDs is reported by incorporating 1,3,5‐tris(1‐phenyl‐1H‐benzimidazol‐2‐yl)benzene (TPBi) doped conjugated amino‐alkyl substituted polyfluorene poly[(9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] (PFN) electron injection layer, achieving a maximum luminance of 9875 cd m⁻², a high current efficiency of 10.41 cd A⁻¹, and an external quantum efficiency of 3.19%. Since the solvents used for perovskite precursors and PFN are orthogonal, the protected and complete interface of perovskite film and CTL is effectively obtained by solution processes. The doping of TPBi into PFN not only enhances the capability of electron injection, but also significantly suppresses the emission quenching of perovskite films caused by the charge transfer between perovskite and PFN due to the reduced difference in their work functions. This work provides an efficient approach for the development of all‐solution‐processed PeLEDs.

Thanks to the strong electron‐donating capability of carbon–oxygen‐bridged (CO‐bridged) ladder‐type building blocks, CO‐bridged nonfullerene acceptors (NFAs) present low bandgaps and strong light‐harvesting capability, delivering high short‐circuit current density (>28 mA cm⁻²) and high power conversion efficiency (>14% for single‐junction and >17% for tandem) in organic solar cells.

Abstract

Recently, acceptor–donor–acceptor (A–D–A) small molecules have emerged as promising nonfullerene acceptors (NFAs) for organic solar cells and have attracted great attention. The carbon‐bridged (C‐bridged) ladder‐type D unit plays a crucial role in developing high‐performance A–D–A NFAs. However, the medium electron‐donating capability of C‐bridged units is unfavorable for making NFAs with strong light‐harvesting capability. In this regard, carbon–oxygen‐bridged (CO‐bridged) ladder‐type units present advantages in developing strong light‐absorbing NFAs. Here, recent progress in the newly emerging CO‐bridged NFAs is highlighted. The synthetic methods for the polycyclic CO‐bridged building blocks are introduced. The photovoltaic performance for CO‐bridged NFAs is summarized and discussed. Perspectives on developing high‐performance CO‐bridged‐NFA‐based solar cells are made.

The latest progress in exciton–photon coupling of perovskite materials is reviewed. Polaritons in planar and nanowire Fabry–Pérot microcavities are discussed predominantly in terms of materials and photophysics. Large Rabi‐splitting energy (≈656 meV) is achieved in CsPbBr₃. These large values enable polariton condensation and polariton lasers to be realized at high temperature or in low‐Q cavities.

Abstract

The semiconductor exciton–polariton, arising from the strong coupling between excitons and confined cavity photon modes, is not only of fundamental importance in macroscopic quantum effects but also has wide application prospects in ultralow‐threshold polariton lasers, slowing‐light devices, and quantum light sources. Very recently, metallic halide perovskites have been considered as a great candidate for exciton–polariton devices owing to their low‐cost fabrication, large exciton oscillator strength, and binding energy. Herein, the latest progress in exciton–polaritons and polariton lasers of perovskites are reviewed. Polaritons in planar and nanowires Fabry–Pérot microcavities are discussed with particular reference to material and photophysics. Finally, a perspective on the remaining challenges in perovskite polaritons research is given.

Interfaces between the photoactive layer and electrodes play a critical role in ultimate device behaviors in organic bulk heterojunction solar cells (OSCs) and hybrid halide perovskite solar cells (PSCs). Recent progress in interface modification for OSCs and PSCs aimed at improving interfacial charge extraction and mitigating surface recombination, and at enhancing trap passivation and device stability is presented.

Abstract

Organic bulk heterojunction solar cells (OSCs) and hybrid halide perovskite solar cells (PSCs) are two promising photovoltaic techniques for next‐generation energy conversion devices. The rapid increase in the power conversion efficiency (PCE) in OSCs and PSCs has profited from synergetic progresses in rational material synthesis for photoactive layers, device processing, and interface engineering. Interface properties in these two types of devices play a critical role in dictating the processes of charge extraction, surface trap passivation, and interfacial recombination. Therefore, there have been great efforts directed to improving the solar cell performance and device stability in terms of interface modification. Here, recent progress in interfacial doping with biopolymers and ionic salts to modulate the cathode interface properties in OSCs is reviewed. For the anode interface modification, recent strategies of improving the surface properties in widely used PEDOT:PSS for narrowband OSCs or replacing it by novel organic conjugated materials will be touched upon. Several recent approaches are also in focus to deal with interfacial traps and surface passivation in emerging PSCs. Finally, the current challenges and possible directions for the efforts toward further boosts of PCEs and stability via interface engineering are discussed.