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Te4+-doped Cs2ZrCl6 vacancy-ordered perovskites with excitation wavelength-dependent tunable color have been synthesised by a simple precipitation method at room temperature, with two luminescent centres originating from the Te4+ and the STE (self-trapping exciton) of the Cs2ZrCl6 itself, respectively. They exhibit two different emission characteristics at 254 nm and 365 nm excitation wavelengths. At an excitation wavelength of 254 nm, the emission characteristics allow Te4+-doped Cs2ZrCl6 to exhibit tunable emission from blue to white to yellow under the control of Te4+ doping. And the excitation wavelength of 365 nm shows yellow emission. Te4+ doped Cs2ZrCl6 phosphors were used for optical anti-counterfeiting, and the anti-counterfeiting patterns were well distinguished under 254 nm and 365 nm UV lamps, demonstrating the potential of this excitation wavelength-dependent tunable color material for optical anti-counterfeiting applications. [ABSTRACT FROM AUTHOR]

Highlights: High-quality large-area perovskite films are prepared using a solid–liquid two-step film formation method combined with CsBr modification for the buried interface and Urea additive for perovskite crystallization. The inverted perovskite solar modules' performance is enhanced to 20.56% in 61.56 cm2 with improved stability. A considerable efficiency gap exists between large-area perovskite solar modules and small-area perovskite solar cells. The control of forming uniform and large-area film and perovskite crystallization is still the main obstacle restricting the efficiency of PSMs. In this work, we adopted a solid–liquid two-step film formation technique, which involved the evaporation of a lead iodide film and blade coating of an organic ammonium halide solution to prepare perovskite films. This method possesses the advantages of integrating vapor deposition and solution methods, which could apply to substrates with different roughness and avoid using toxic solvents to achieve a more uniform, large-area perovskite film. Furthermore, modification of the NiOx/perovskite buried interface and introduction of Urea additives were utilized to reduce interface recombination and regulate perovskite crystallization. As a result, a large-area perovskite film possessing larger grains, fewer pinholes, and reduced defects could be achieved. The inverted PSM with an active area of 61.56 cm2 (10 × 10 cm2 substrate) achieved a champion power conversion efficiency of 20.56% and significantly improved stability. This method suggests an innovative approach to resolving the uniformity issue associated with large-area film fabrication. [ABSTRACT FROM AUTHOR]

At present, tuning the luminescence characteristics of phosphors by external physical stimuli such as temperature and pressure has attracted the interest of researchers. However, the emission-tunable luminescence processes by temperature or pressure in lead-free perovskite with ordered vacancy materials have not been systematically studied. In this study, Bi3+-doped Rb2SnCl6 crystals were successfully synthesized using a simple precipitation method, and these crystals demonstrated a remarkable enhancement of luminescence intensity compared with the unannealed ones at 140–200 °C, and with a red-shift in the emission peak from 450 to 500 nm. It was found that the annealing treatment increased the Bi–Cl bond length leading to emission red-shift and achieved the change in the emission intensity due to the band gap modulation of the material. Furthermore, a candidate material for the color-changing optical security strategies was obtained by combining the Bi3+-doped Rb2SnCl6 phosphor and printing ink. This work is a valuable reference for the rational design of luminescent perovskites with promising new functionalities and stimulates the great potential of luminescent perovskites in developing promising phosphors for advanced anticounterfeiting. [ABSTRACT FROM AUTHOR]

Development of suitable hole transport materials is vital for perovskite solar cells (PSCs) to diminish the energy barrier and minimize the potential loss. Here, a low-cost hole transport molecule named SFX-POCCF3 (23.72 $/g) is designed with a spiro[fluorene-9,9'-xanthene] (SFX) core and terminated by trifluoroethoxy units. Benefiting from the suitable energy level, high hole mobility, and better charge extraction and transport, the PSCs based on SFX-POCCF3 exhibit improved open-circuit voltage by 0.02 V, therefore, the PSC device based on SFX-POCCF3 exhibits a champion PCE of 21.48%, which is comparable with the control device of Spiro-OMeTAD (21.39%). More importantly, the SFX-POCCF3 based PSC possesses outstanding light stability, which retains 95% of the initial efficiency after about 1,000 h continuous light soaking, which is in accordance with the result continuous output at maximum power point. Whereas, Spiro-OMeTAD witnesses a rapid decrease to 80% of its original efficiency after 100 h light soaking. This work demonstrated that an efficient alignment of energy levels between HTL and perovskite will lead to significant highly efficient PSCs with remarkably enhanced light stability. [ABSTRACT FROM AUTHOR]

Wide‐bandgap (WBG) perovskite solar cells (PSCs) have garnered significant attention for their potential applications in tandem solar cells. However, their large open‐circuit voltage (VOC) deficit and serious photo‐induced halide segregation remain the main challenges that impede their applications. Herein, a post‐treatment strategy without thermal annealing is presented to form a 2D top layer of 2‐thiopheneethylammonium lead halide (n = 1) on WBG perovskites. This thermal annealing‐free post‐treatment method can more effectively passivate the defects of WBG methylamine (MA)‐free formamidinium/cesium lead iodide/bromide perovskite films and suppress photo‐induced perovskite phase segregation, as compared with the thermal annealing method that yields multi‐2D phases. The resulting opaque and semi‐transparent 1.66 eV‐bandgap perovskite solar cells deliver maximum power conversion efficiencies of 21.47% (a small VOC deficit of 0.43 V) and 19.11%, respectively, both of which are among the highest reports for inverted MA‐free WBG PSCs. Consequently, four‐terminal all‐perovskite tandem cells realize a remarkable efficiency of 26.64%, showing great promise for their applications in efficient multi‐junction tandem solar cells. [ABSTRACT FROM AUTHOR]

The delicate engineering of monovalent cations in perovskite material has led to continuous performance breakthroughs and stability improvement for the perovskite light‐emitting diodes (PeLEDs). However, the exact role of A‐site cations on the electroluminescence (EL) performance and degradation mechanism of PeLEDs has not been systematically answered yet. Herein, it is demonstrated that the most commonly used methylammonium cation (MA+) has an adverse effect on the electrochemical reaction at the interface between perovskite and metal‐oxide layer, leading to deteriorated EL performance as compared to that of the formamidinium cation (FA+)‐based perovskite. It reveals that the accelerated deprotonation process of MA+ under an electric field will aggravate the reaction between iodide and metal ion in oxide layer. The further substitution of a small portion of FA+ with inorganic cesium cation (Cs+) results in much enhanced crystallinity and enlarged crystal size, leading to an optimized peak external quantum efficiency of 21.3%. The ion migration process in the PeLEDs can be significantly suppressed with Cs+ incorporation, leading to a smaller roll‐off under large current density and an elongated half‐lifetime of 190.1 h under a current density of 20 mA cm‐2, representing one of the most stable PeLEDs based on 3D perovskite layer. [ABSTRACT FROM AUTHOR]

Tin halide perovskite solar cells (TPSCs) have attracted extensive attention because of their low toxicity and high theoretical efficiency. However, rapid crystallization, rich defects, and easy oxidation of tin‐based perovskite films seriously restrict solar cell performance. Herein, a composition and additive engineering solution by removing commonly used tin fluoride additive from formamidinium tin triiodide perovskite precursors and replacing it with excess tin (II) iodide and ethylenediamine dihydroiodide (EDAI2) is adopted. The presence of EDAI2 and excess SnI2 and the absence of SnF2 enable tin‐based perovskite films with greatly improved morphology, enhanced crystalline quality, boosted optical properties, and prolonged carrier lifetime. Therefore, the SnF2‐free non‐stoichiometric TPSCs employing the EDAI2 additive and excess SnI2 have increased built‐in potential, lowered dark currents, and reduced carrier recombination. The resulting SnF2‐free and SnI2‐rich TPSCs with EDAI2 addition realize a steady‐state efficiency of 10.0%, which is one of the highest power conversion efficiencies among the SnF2‐free TPSCs, along with considerably improved light stability. This work highlights the crucial roles of additives in TPSCs and provides an effective strategy to fabricate efficient and stable low‐toxic lead‐free perovskite solar cells. [ABSTRACT FROM AUTHOR]

Red LEDs excited by blue light have a wide range of applications in plant growth due to their simple structure. The preparation of efficient red phosphors has attracted much attention from researchers. In this paper, Cs 2 NaGdCl 6 :Ho3+ Sb3+ phosphors were synthesized by the solvothermal method, which produced the characteristic emission of Ho3+ 5 F5→ 5 I8 at 655 nm under 460 nm excitation. The red light at 655 nm is further enhanced after the introduction of Sb3+, and the quantum efficiency can reach 39.85 %. The luminescence mechanism and energy transfer of Sb3+ and Ho3+ were further investigated. The produced phosphor was encapsulated with a 460 nm blue chip into an LED to realize red and blue dual emission, which meets the demand for blue and red light for plant growth. • A double perovskites phosphor Cs 2 NaGdCl 6 :Ho3+ Sb3+ was synthesized. • The emission spectrum excited by the blue light chip matches well with the plant absorption spectrum. • Synthesis of a halide double perovskites with good thermal stability. • The materials show promising application in the field of plant cultivation. [ABSTRACT FROM AUTHOR]

Wide-bandgap pure bromide-based hybrid perovskite solar cells (PSCs), with the advantages of high open-circuit voltage, and superior environmental stability, have potential applications in tandem solar cells and building-integrated photovoltaics. However, the open-circuit voltage (Voc) and the power conversion efficiency (PCE) of bromide-based PSCs are relatively low. In this work, a bathocuproine (BCP) interlayer, instead of conventional PCBM, was employed between the FAPbBr3 absorber and electron transport layer (ETL). The resulting energy level difference of FAPbBr3/BCP was much lower compared with that of FAPbBr3/PCBM, which was expected to facilitate the charge transport. More importantly, it was demonstrated that the BCP interlayer had strong passivation on the FAPbBr3 surface through coordination of N and Pb as well as N-H hydrogen bonding. Accordingly, the inverted planar FAPbBr3 PSC possessed a high PCE of 8.02% and Voc of 1.430 V. In addition, the PSCs with a BCP buffer layer exhibited better air stability compared with that with PCBM films. This work provides new insight into the BCP interlayer, which has dual functions as surface passivation and energy level alignment with FAPbBr3 films, paving the way toward realizing high-performance FAPbBr3 perovskite solar cells. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) represent a promising next‐generation photovoltaic technology considering their high efficiency and low cost. At the current stage, resolving the stability bottleneck is extremely urgent to realize PSCs' commercialization since the efficiencies of these cells are improved to a level comparable to that of crystalline silicon solar cells. Similar to other functional layers, a proper choice of the rear electrode atop the perovskite layer is equally important for achieving the device's long‐term stability. This topic has not been comprehensively reviewed before. Here, recent progress in the development of rear electrodes based on metals, carbon‐based materials, transparent conductive oxides, and conductive polymers is summarized, especially focusing on their different impacts on the device's long‐term stability and associated degradation mechanisms. In the context of practical applications, the impacts of rear electrode materials on the device's overall efficiency and cost‐effectiveness are also discussed. [ABSTRACT FROM AUTHOR]

Single matrix white luminescent materials are relatively rare. Here, we report an excitation wavelength-dependent Cs2HfCl6:xSb (CHC:xSb) vacancy-ordered double perovskite where, by adjusting the excitation wavelength, different types of white light emission can be obtained. [ABSTRACT FROM AUTHOR]

Organic light emitting diodes (OLEDs) employing organic thin‐film based emitters have attracted tremendous attention due to their widespread applications in lighting and as displays in mobile devices and televisions. The novel thin‐film photovoltaic techniques using organic or organic–inorganic hybrid materials such as organic photovoltaics (OPVs) and perovskite solar cells (PSCs) have become emerging competitive candidates with regard to the traditional photovoltaic techniques on account of high‐efficiency, low‐cost, and simple manufacturing processing properties. However, OLEDs, OPVs, and PSCs are vulnerable to the undesired degradation induced by moisture and oxygen. To afford long‐term stability, a robust encapsulation technique by employing materials and structures that possess high barrier performance against oxygen and moisture must be explored and employed to protect these devices. Herein, the recent progress on specific encapsulation materials and techniques for three types of devices on the basis of fundamental understanding of device stability is reviewed. First, their degradation mechanisms, as well as, influencing factors are discussed. Then, the encapsulation technologies and materials are classified and discussed. Moreover, the advantages and disadvantages of various encapsulation technologies and materials coupled with their encapsulation applications in different devices are compared. Finally, the ongoing challenges and future perspectives of encapsulation frontier are provided. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have attracted much attention in the past decade and their power conversion efficiency has been rapidly increasing to 25.2%, which is comparable with commercialized solar cells. Currently, the long‐term stability of PSCs remains as a major bottleneck impeding their future commercial applications. Beyond strengthening the perovskite layer itself and developing robust external device encapsulation/packaging technology, integration of effective barriers into PSCs has been recognized to be of equal importance to improve the whole device's long‐term stability. These barriers can not only shield the critical perovskite layer and other functional layers from external detrimental factors such as heat, light, and H2O/O2, but also prevent the undesired ion/molecular diffusion/volatilization from perovskite. In addition, some delicate barrier designs can simultaneously improve the efficiency and stability. In this review article, the research progress on barrier designs in PSCs for improving their long‐term stability is reviewed in terms of the barrier functions, locations in PSCs, and material characteristics. Regarding specific barriers, their preparation methods, chemical/photoelectronic/mechanical properties, and their role in device stability, are further discussed. On the basis of these accumulative efforts, predictions for the further development of effective barriers in PSCs are provided at the end of this review. [ABSTRACT FROM AUTHOR]

Fullerene derivatives, which possess extraordinary geometric shapes and high electron affinity, have attracted significant attention for thin film technologies. This study demonstrates an important photovoltaic application using carboxyl-functionalized carbon buckyballs, C60 pyrrolidine tris-acid (CPTA), to fabricate electron transport layers (ETLs) that replace traditional metal oxide-based ETLs in efficient and stable n-i-p-structured planar perovskite solar cells (PSCs). The uniform CPTA film is covalently anchored onto the surface of indium tin oxide (ITO), significantly suppressing hysteresis and enhancing the flexural strength in the CPTA-modified PSCs. Moreover, solution-processable CPTA-based ETLs also enable the fabrication of lightweight flexible PSCs. The maximum-performing device structures composed of ITO/CPTA/CH3NH3PbI3/2,2′,7,7′-tetrakis-( N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD)/Au yield power conversion efficiencies of more than 18% on glass substrates and up to 17% on flexible substrates. These results indicate that the CPTA layers provide new opportunities for solution-processed organic ETLs by substantially simplifying the procedure for fabricating PSCs for portable applications. [ABSTRACT FROM AUTHOR]

The crystal phase and energy band adjustment of halide perovskites have become the focus of research. Sb3+ doped lead-free indium-based perovskites A 2 InX 5 ·H 2 O:Sb3+ (A=Cs+, Rb+; X = Cl-, Br-) are synthesized at room temperature. Through changing the crystal phase structure, an intelligent anti-counterfeiting material is used to monitor water vapor and high temperature. Moreover, the Rb 2 InBr 5 ·H 2 O:Sb3+ achieves broadband near-infrared (NIR) emission with a high photoluminescence quantum efficiency (PLQY) of 54.3%. The NIR light-emitting diode shows that the device can effectively achieve NIR imaging. Theoretical calculations further clarified that the regular changes in luminescence originate from energy band modulation. This work provides a broader sight for the synthesis, luminescence mechanism and application of indium-based perovskite. • Indium-based perovskite with controllable luminescence properties was synthesized at room temperature. • The reversible change of crystal phase is used for smart anti-counterfeiting. • High-efficiency quantum yield of Rb 2 InBr 5 ·H 2 O:Sb3+ is used in near-infrared light-emitting diodes. • Theoretical calculation combined with experiments prove that broadband emission originate from band gap adjustment. [ABSTRACT FROM AUTHOR]

This work reports on incorporation of spectrally tuned gold/silica (Au/SiO2) core/shell nanospheres and nanorods into the inverted perovskite solar cells (PVSC). The band gap of hybrid lead halide iodide (CH3NH3PbI3) can be gradually increased by replacing iodide with increasing amounts of bromide, which can not only offer an appreciate solar radiation window for the surface plasmon resonance effect utilization, but also potentially result in a large open circuit voltage. The introduction of localized surface plasmons in CH3NH3PbI2.85Br0.15‐based photovoltaic system, which occur in response to electromagnetic radiation, has shown dramatic enhancement of exciton dissociation. The synchronized improvement in photovoltage and photocurrent leads to an inverted CH3NH3PbI2.85Br0.15 planar PVSC device with power conversion efficiency of 13.7%. The spectral response characterization, time resolved photoluminescence, and transient photovoltage decay measurements highlight the efficient and simple method for perovskite devices. [ABSTRACT FROM AUTHOR]

Replacement of the ZrO2 insulator layer in the state-of-the-art TiO2/ZrO2/carbon structure by mesoscopic p-type NiO particles led to 39% increase of energy conversion efficiency of hole-conductor-free organometallic perovskite heterojunction solar cells with carbon counter electrodes. In these cells, the light absorber, CH3NH3PbI3, formed instantly inside the pores of the entire TiO2/NiO/carbon layer upon sequential deposition of PbI2 and CH3NH3I. Photoluminescence, impedance spectroscopy and transient photovoltage decay measurements have revealed that introduction of NiO extended the electron lifetime and augmented the hole extraction of the counter electrode. As a result, the photocurrent and open-circuit voltage both increased, resulting in a cell with impressive energy conversion efficiency of 11.4% under AM1.5G conditions. [ABSTRACT FROM AUTHOR]

Planar heterojunction perovskite solar cells were fabricated through a low temperature approach. We find that the device performance significantly depends on the external bias before and during measurements. By appropriate optimization of the bias conditions, we could achieve an 8-fold increase in the power conversion efficiency. The significant improvement in device performance might be caused by the ion motion in the perovskite under the external electric field. [ABSTRACT FROM AUTHOR]

• The phase transition temperature of Sr 3 Sn 2 O 7 is reduced by Ba doping. • The phase transition is related to SnO 6 octahedron vibration mode. • The doping of Ba aggravates the anharmonic effect of some vibration modes. The ceramics of Sr 3- x Ba x Sn 2 O 7 (0 ≤ x ≤ 0.6) were synthesized by solid-state reaction method. The lattice constants of Sr 3- x Ba x Sn 2 O 7 increase with increasing of Ba doping. With increasing of the Ba2+ concentration from x = 0 to x = 0.2, the phase transition temperature reduces by 73 K. The vibration modes related to the phase transitions are strongly related to the tilting and rotation of SnO 6 octahedra. The doping of Ba significantly aggravates the anharmonic effect and increases the Raman activity of the vibration mode A 2 (5) , and reduces the phonon lifetime and the Raman activity of the vibration mode A 1 17 . [ABSTRACT FROM AUTHOR]

Abstract The power conversion efficiency (PCE) of perovskite solar cells (PSCs) keeps decreasing after a period of time. This has remained a concern in commercializing PSCs. Researchers have attempted to slow down the degeneration of the cell. In this paper, a facile freeze treatment was applied to increase the PCE of degenerated PSCs. Through freeze treatment, the carrier recombination in the cell was significantly reduced, thus improving the open-circuit voltage by 3% and increasing the PCE from 8.34% to 9.23%. Compared with the nontreated one, the time spent was more than 200% for the PCE to decrease from 8% to 6% after three cycles of freeze treatment. [ABSTRACT FROM AUTHOR]

Abstract Novel small-molecules, B2T and B2F, based on benzobis(thiadiazole) have been designed and synthesized as electron transporting materials for perovskite solar cells (PSCs). Benefiting from the high electron affinity of benzobis(thiadiazole) unit, both B2T and B2F exhibited an efficient electron transporting ability in CH 3 NH 3 PbI 3-x Cl x planar-heterojunction (PHJ) PSCs. The device based on B2T exhibited an optimal power-conversion efficiency (PCE) of 13.0%, while that of B2F was 15.0% with a relatively low hysteresis. Compared to B2T device, the higher efficiency of B2F device was mainly due to the impressive increase in short-circuit current density (J SC), from 19.36 mA cm−2 to 22.13 mA cm−2. By comprehensive analysis of the energy level and photoluminescence spectra of the devices, we inferred that the higher J SC was resulted from the lower highest occupied molecular orbital (HOMO) energy level of B2F than B2T, which induced a more efficient hole-blocking and less recombination of charge carriers. Through the molecular design (from thiophene to fluorene), we developed a highly efficient electron transporting material, this strategy may provide a new building block to develop novel efficient interface materials for PSCs. Graphical abstract Two benzobis(thiadiazole)-based small molecules (B2T and B2F) were designed and synthesized. Simply by tuning the donor groups from thiophenes to fluorenes, perovskite solar cells with B2F as electron transporting layer exhibited a high power conversion efficiency of 15%. fx1 Highlights • Simply by tuning the donor groups from thiophenes to fluorenes, two effective electron transport materials were designed and synthesized, the they were used to the inverted perovskite solar cells. this may provide a new building block to develop novel efficient interface materials. • The device based on B2T exhibited an optimal power-conversion efficiency (PCE) of 13.0%, while that of B2F was 15.0% with a relatively low hysteresis. the higher efficiency of B2F device was mainly due to the impressive increase in short-circuit current density (JSC), from 19.36 mA cm−2 to 22.13 mA cm−2. • The higher JSC of B2F device resulted from the lower highest occupied molecular orbital (HOMO) energy level of B2F than B2T, which induced a more efficient hole-blocking and less recombination of charge carriers. [ABSTRACT FROM AUTHOR]

Hole-transporting materials play an important role in perovskite solar cells. In this study, we introduced a novel hole-transporting material without p-type dopant, a tetrathiafulvalene derivative anchored with eight carboxyl groups (TTA) into inverted structure perovskite solar cells. The devices with TTA as hole-transporting layer showed high power conversion efficiency of 16.7%, which was 44.5% improvement compared with the reference devices without hole-transporting layer. The performance improvement was ascribed to three factors: 1) the better match of energy level between ITO and perovskite layer; 2) enhanced hole extraction at anode interface; 3) improved perovskite morphology. [ABSTRACT FROM AUTHOR]

A conjugated polymer poly (9,9-dioctyfluorene-co-benzothiazole) (F8BT) was used as the electron transporting layer (ETL) to modify the cathode interface of inverted planar perovskite solar cell. Incorporation of the thin F8BT layer delivered greatly enhanced power conversion efficiency (PCE) of 13.9% compared to the PCE 7.9% of the device without F8BT, due to the improvements in various performance parameters like V oc , J sc and FF . Moreover, great elimination of the hysteresis was demonstrated in F8BT based devices. These results suggest promising potential of polymeric materials in perovskite solar cells and possible approach to eliminate the hysteresis of perovskite solar cells with this class of interfacial materials. [ABSTRACT FROM AUTHOR]

The solution-processable electron transport layer (ETL) is essential for the electron transport and extraction of inverted perovskite solar cells (PSCs). A new naphthalene diimide based copolymer with phosphite ester pendants (PFNDI) is developed as an ETL in inverted PSCs. The naphthalene diimide backbone and the phosphite ester pendants endow PFNDI a good electron transport property and a strong binding force on perovskite. By introducing PFNDI on the perovskite interface, we succeed in improving surface morphologies of perovskite film, reducing the trap density and facilitating electron transport properties. The PFNDI-based devices exhibit an optimal power conversion efficiency of 18.25% (with the V OC = 1.068 V, J SC = 22.53 mA cm−2 and FF = 75.85%) and fine long-term stabilities. The un-encapsulated PFNDI-based devices maintain 80% of their initial performance after storage for more than 500 h at 20 °C in air with a relative humidity of 25% and 75% of their initial efficiency after continuously heating for about 300 h. Our work demonstrated that NDI-based polymers with proper pendant groups can be the ideal n-type organic materials for high-performance PSCs. Image 1 • A new naphthalene diimide based copolymer was synthesized and introduced into PSCs. • The copolymer improves the charge transport properties to deliver a PCE of 18.25%. • Our findings may pave a new way to design promising non-fullerene-based ETL. [ABSTRACT FROM AUTHOR]