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1.
Creating defect tolerant lead‐free halide perovskites is the major challenge for development of high‐performance photovoltaics with nontoxic absorbers. Few compounds of Sn, Sb, or Bi possess ns2 electronic configuration similar to lead, but their poor photovoltaic performances inspire us to evaluate other factors influencing defect tolerance properties. The effect of heavy metal cation (Bi) transmutation and ionic migration on the defects and carrier properties in a 2D layered perovskite (NH4)3(Sb(1?x)Bix)2I9 system is investigated. It is shown, for the first time, the possibility of engineering the carriers in halide perovskites via metal cation transmutation to successfully form intrinsic p‐ and n‐type materials. It is also shown that this material possesses a direct–indirect bandgap enabling high absorption coefficient, extended carrier lifetimes >100 ns, and low trap densities similar to lead halide perovskites. This study also demonstrates the possibility of electrical poling to induce switchable photovoltaic effect without additional electron and hole transport layers.  相似文献   

2.
Perovskite solar cells increasingly feature mixed‐halide mixed‐cation compounds (FA1?x?yMAxCsyPbI3?zBrz) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti‐solvent processing window for the fabrication of high‐quality films and efficient solar cells. This window widens from seconds, in the case of single cation/halide systems (e.g., MAPbI3, FAPbI3, and FAPbBr3), to several minutes for mixed systems. In situ X‐ray diffraction studies reveal that the processing window is closely related to the crystallization of the disordered sol–gel and to the number of crystalline byproducts; the processing window therefore depends directly on the precise cation/halide composition. Moreover, anti‐solvent dripping is shown to promote the desired perovskite phase with careful formulation. The processing window of perovskite solar cells, as defined by the latest time the anti‐solvent drip yields efficient solar cells, broadened with the increasing complexity of cation/halide content. This behavior is ascribed to kinetic stabilization of sol–gel state through cation/halide engineering. This provides guidelines for designing new formulations, aimed at formation of the perovskite phase, ultimately resulting in high‐efficiency perovskite solar cells produced with ease and with high reproducibility.  相似文献   

3.
Both conductivity and mobility are essential to charge transfer by carrier transport layers (CTLs) in perovskite solar cells (PSCs). The defects derived from generally used ionic doping method lead to the degradation of carrier mobility and parasite recombinations. In this work, a novel molecular doping of NiOx hole transport layer (HTL) is realized successfully by 2,2′‐(perfluoronaphthalene‐2,6‐diylidene)dimalononitrile (F6TCNNQ). Determined by X‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, the Fermi level (EF) of NiOx HTLs is increased from ?4.63 to ?5.07 eV and valence band maximum (VBM)‐EF declines from 0.58 to 0.29 eV after F6TCNNQ doping. The energy level offset between the VBMs of NiOx and perovskites declines from 0.18 to 0.04 eV. Combining with first‐principle calculations, electrostatic force microscopy is applied for the first time to verify direct electron transfer from NiOx to F6TCNNQ. The average power conversion efficiency of CsFAMA mixed cation PSCs is boosted by ≈8% depending on F6TCNNQ‐doped NiOx HTLs. Strikingly, the champion cell conversion efficiency of CsFAMA mixed cations and MAPbI3‐based devices gets to 20.86% and 19.75%, respectively. Different from passivation effect, the results offer an extremely promising molecular doping method for inorganic CTLs in PSCs. This methodology definitely paves a novel way to modulate the doping in hybrid electronics more than perovskite and organic solar cells.  相似文献   

4.
Following the rejuvenation of 3D organic–inorganic hybrid perovskites, like CH3NH3PbI3, (quasi)‐2D Ruddlesden–Popper soft halide perovskites R2An?1PbnX3n+1 have recently become another focus in the optoelectronic and photovoltaic device community. Although quasi‐2D perovskites were first introduced to stabilize optoelectronic/photovoltaic devices against moisture, more interesting properties and device applications, such as solar cells, light‐emitting diodes, white‐light emitters, lasers, and polaritonic emission, have followed. While delicate engineering design has pushed the performance of various devices forward remarkably, understanding of the fundamental properties, especially the charge‐transfer process, electron–phonon interactions, and the growth mechanism in (quasi)‐2D halide perovskites, remains limited and even controversial. Here, after reviewing the current understanding and the nexus between optoelectronic/photovoltaic properties of 2D and 3D halide perovskites, the growth mechanisms, charge‐transfer processes, vibrational properties, and electron–phonon interactions of soft halide perovskites, mainly in quasi‐2D systems, are discussed. It is suggested that single‐crystal‐based studies are needed to deepen the understanding of the aforementioned fundamental properties, and will eventually contribute to device performance.  相似文献   

5.
Organic–inorganic metal halide perovskites (e.g., CH3NH3PbI3?x Clx ) emerge as a promising optoelectronic material. However, the Shockley–Queisser limit for the power conversion efficiency (PCE) of perovskite‐based photovoltaic devices is still not reached. Nonradiative recombination pathways may play a significant role and appear as photoluminescence (PL) inactive (or dark) areas on perovskite films. Although these observations are related to the presence of ions/defects, the underlying fundamental physics and detailed microscopic processes, concerning trap/defect status, ion migration, etc., still remain poorly understood. Here correlated wide‐field PL microscopy and impedance spectroscopy are utilized on perovskite films to in situ investigate both the spatial and the temporal evolution of these PL inactive areas under external electric fields. The formation of PL inactive domains is attributed to the migration and accumulation of iodide ions under external fields. Hence, we are able to characterize the kinetic processes and determine the drift velocities of these ions. In addition, it is shown that I2 vapor directly affects the PL quenching of a perovskite film, which provides evidence that the migration/segregation of iodide ions plays an important role in the PL quenching and consequently limits the PCE of organometal halide‐based perovskite photovoltaic devices.  相似文献   

6.
Cesium lead halide (CsPbX3) perovskite has emerged as a promising low‐threshold multicolor laser material; however, realizing wavelength‐tunable lasing output from a single CsPbX3 nanostructure is still constrained by integrating different composition. Here, the direct synthesis of composition‐graded CsPbBrxI3?x nanowires (NWs) is reported through vapor‐phase epitaxial growth on mica. The graded composition along the NW, with an increased Br/I from the center to the ends, comes from desynchronized deposition of cesium lead halides and temperature‐controlled anion‐exchange reaction. The graded composition results in varied bandgaps along the NW, which induce a blueshifted emission from the center to the ends. As an efficient gain media, the nanowire exerts position‐dependent lasing performance, with a different color at the ends and center respectively above the threshold. Meanwhile, dual‐color lasing with a wavelength separation of 35 nm is activated simultaneously at a site with an intermediate composition. This position‐dependent dual‐color lasing from a single nanowire makes these metal halide perovskites promising for applications in nanoscale optical devices.  相似文献   

7.
Mixed‐halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution‐processed triple‐cation mixed‐halide (Cs0.06MA0.15FA0.79)Pb(Br0.4I0.6)3 perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar‐equivalent illumination. It is found that the illumination leads to localized surface sites of iodide‐rich perovskite intermixed with passivating PbI2 material. Time‐ and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide‐rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed‐halide mixed‐cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures.  相似文献   

8.
The mixed cation lead mixed halide perovskite (MLMP) CsxFA1‐xPbIyBr3‐y is one of the most promising candidates for both single‐junction and tandem solar cells due to its high efficiency and remarkable stability. However, the composition effect on thermal stability and photovoltaic performances has not yet been comprehensively investigated. Therefore, the interplay between composition, crystal structure, morphology, and optoelectronic properties under heat stress, is systematically elucidated here through a series of in situ characterizations. It is revealed for the first time that the FA+ and Br? release synchronously at first even under mild annealing. This leads to a serious FA‐ and Br‐deficiency issue, with only 88.3% of Br and 90.2% of FA retained after annealing at 100 °C, which significantly magnifies the hysteresis, phase segregation, and instability issues. Finally, a trace amount of FA+ and Br? is introduced onto the post‐annealed MLMP surface to compensate for the deficiency through vacancy filling. The degradation lifetime to 80% of the initial efficiency (t80) is improved from 504 to 1056 h and the hysteresis issue is also well resolved. This work highlights the importance of the synergetic composition effect of the organic cation and halide anion on stability and efficiency optimization for long‐term applications.  相似文献   

9.
The combination of high‐capacity and long‐term cycling stability is an important factor for practical application of anode materials for lithium‐ion batteries. Herein, NixMnyCozO nanowire (x + y + z = 1)/carbon nanotube (CNT) composite microspheres with a 3D interconnected conductive network structure (3DICN‐NCS) are prepared via a spray‐drying method. The 3D interconnected conductive network structure can facilitate the penetration of electrolyte into the microspheres and provide excellent connectivity for rapid Li+ ion/electron transfer in the microspheres, thus greatly reducing the concentration polarization in the electrode. Additionally, the empty spaces among the nanowires in the network accommodate microsphere volume expansion associated with Li+ intercalation during the cycling process, which improves the cycling stability of the electrode. The CNTs distribute uniformly in the microspheres, which act as conductive frameworks to greatly improve the electrical conductivity of the microspheres. As expected, the prepared 3DICN‐NCS demonstrates excellent electrochemical performance, showing a high capacity of 1277 mAh g?1 at 1 A g?1 after 2000 cycles and 790 mAh g?1 at 5 A g?1 after 1000 cycles. This work demonstrates a universal method to construct a 3D interconnected conductive network structure for anode materials  相似文献   

10.
Low‐dimensional Ruddlesden–Popper (LDRP) perovskites are a current theme in solar energy research as researchers attempt to fabricate stable photovoltaic devices from them. However, poor exciton dissociation and insufficiently fast charge transfer slows the charge extraction in these devices, resulting in inferior performance. 1,4‐Butanediamine (BEA)‐based low‐dimensional perovskites are designed to improve the carrier extraction efficiency in such devices. Structural characterization using single‐crystal X‐ray diffraction reveals that these layered perovskites are formed by the alternating ordering of diammonium (BEA2+) and monoammonium (MA+) cations in the interlayer space (B‐ACI) with the formula (BEA)0.5MAn PbnI3n+1. Compared to the typical LDRP counterparts, these B‐ACI perovskites deliver a wider light absorption window and lower exciton binding energies with a more stable layered perovskite structure. Additionally, ultrafast transient absorption indicates that B‐ACI perovskites exhibit a narrow distribution of quantum well widths, leading to a barrier‐free and balanced carrier transport pathway with enhanced carrier diffusion (electron and hole) length over 350 nm. A perovskite solar cell incorporating BEA ligands achieves record efficiencies of 14.86% for (BEA)0.5MA3Pb3I10 and 17.39% for (BEA)0.5Cs0.15(FA0.83MA0.17)2.85Pb3(I0.83Br0.17)10 without hysteresis. Furthermore, the triple cations B‐ACI devices can retain over 90% of their initial power conversion efficiency when stored under ambient atmospheric conditions for 2400 h and show no significant degradation under constant illumination for over 500 h.  相似文献   

11.
The morphology of hybrid organic–inorganic perovskite films is known to strongly affect the performance of perovskite‐based solar cells. CH3NH3PbI3‐xClx (MAPbI3‐xClx) films have been previously fabricated with 100% surface coverage in glove boxes. In ambient air, fabrication generally relies on solvent engineering to obtain compact films. In contrast, this work explores the potential of altering the perovskites microstructure for solar cell engineering. This work starts with CH3NH3PbI3‐xClx, films with grain morphology carefully controlled by varying the deposition speed during the spin‐coating process to fabricate efficient and partially transparent solar cells. Devices produced with a CH3NH3PbI3‐xClx film and a compact thick top gold electrode reach a maximum efficiency of 10.2% but display a large photocurrent hysteresis. As it is demonstrated, the introduction of different concentrations of bromide in the precursor solution addresses the hysteresis issues and turns the film morphology into a partially transparent interconnected network of 1D microstructures. This approach leads to semitransparent solar cells with negligible hysteresis and efficiencies up to 7.2%, while allowing average transmission of 17% across the visible spectrum. This work demonstrates that the optimization of the perovskites composition can mitigate the hysteresis effects commonly attributed to the charge trapping within the perovskite film.  相似文献   

12.
Bismuth‐based compounds have recently gained increasing attention as potentially nontoxic and defect‐tolerant solar absorbers. However, many of the new materials recently investigated show limited photovoltaic performance. Herein, one such compound is explored in detail through theory and experiment: bismuth oxyiodide (BiOI). BiOI thin films are grown by chemical vapor transport and found to maintain the same tetragonal phase in ambient air for at least 197 d. The computations suggest BiOI to be tolerant to antisite and vacancy defects. All‐inorganic solar cells (ITO|NiOx|BiOI|ZnO|Al) with negligible hysteresis and up to 80% external quantum efficiency under select monochromatic excitation are demonstrated. The short‐circuit current densities and power conversion efficiencies under AM 1.5G illumination are nearly double those of previously reported BiOI solar cells, as well as other bismuth halide and chalcohalide photovoltaics recently explored by many groups. Through a detailed loss analysis using optical characterization, photoemission spectroscopy, and device modeling, direction for future improvements in efficiency is provided. This work demonstrates that BiOI, previously considered to be a poor photocatalyst, is promising for photovoltaics.  相似文献   

13.
Organometallic halide perovskites (OMHPs) have attracted broad attention as prospective materials for optoelectronic applications. Among the many anomalous properties of these materials, of special interest are the ferroelectric properties including both classical and relaxor‐like components, as a potential origin of slow dynamics, field enhancement, and anomalous mobilities. Here, ferroelectric properties of the three representative OMHPs are explored, including FAPbxSn1–xI3 (x = 0, x = 0.85) and FA0.85MA0.15PbI3 using band excitation piezoresponse force microscopy and contact mode Kelvin probe force microscopy, providing insight into long‐ and short‐range dipole and charge dynamics in these materials and probing ferroelectric density of states. Furthermore, second‐harmonic generation in thin films of OMHPs is observed, providing a direct information on the noncentrosymmetric polarization in such materials. Overall, the data provide strong evidence for the presence of ferroelectric domains in these systems; however, the domain dynamics is suppressed by fast ion dynamics. These materials hence present the limit of ferroelectric materials with spontaneous polarization dynamically screened by ionic and electronic carriers.  相似文献   

14.
Metal halide perovskites represent a family of the most promising materials for fascinating photovoltaic and photodetector applications due to their unique optoelectronic properties and much needed simple and low‐cost fabrication process. The high atomic number (Z) of their constituents and significantly higher carrier mobility also make perovskite semiconductors suitable for the detection of ionizing radiation. By taking advantage of that, the direct detection of soft‐X‐ray‐induced photocurrent is demonstrated in both rigid and flexible detectors based on all‐inorganic halide perovskite quantum dots (QDs) synthesized via a solution process. Utilizing a synchrotron soft‐X‐ray beamline, high sensitivities of up to 1450 µC Gyair?1 cm?2 are achieved under an X‐ray dose rate of 0.0172 mGyair s?1 with only 0.1 V bias voltage, which is about 70‐fold more sensitive than conventional α‐Se devices. Furthermore, the perovskite film is printed homogeneously on various substrates by the inexpensive inkjet printing method to demonstrate large‐scale fabrication of arrays of multichannel detectors. These results suggest that the perovskite QDs are ideal candidates for the detection of soft X‐rays and for large‐area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.  相似文献   

15.
Rechargeable batteries based on an abundant metal such as aluminum with a three‐electron transfer per atom are promising for large‐scale electrochemical energy storage. Aluminum can be handled in air, thus offering superior safety, easy fabrication, and low cost. However, the development of Al‐ion batteries has been challenging due to the difficulties in identifying suitable cathode materials. This study presents the use of a highly open framework Mo2.5 + y VO9 + z as a cathode for Al‐ion batteries. The open‐tunnel oxide allows a facile diffusion of the guest species and provides sufficient redox centers to help redistribute the charge within the local host lattice during the multivalent‐ion insertion, thus leading to good rate capability with a specific capacity among the highest reported in the literature for Al‐based batteries. This study also presents the use of Mo2.5 + y VO9 + z as a model host to develop a novel ultrafast technique for chemical insertion of Al ions into host structures. The microwave‐assisted method employing diethylene glycol and aluminum diacetate (Al(OH)(C2H3O2)2) can be performed in air in as little as 30 min, which is far superior to the traditional chemical insertion techniques involving moisture‐sensitive organometallic reagents. The Al‐inserted Al x Mo2.5 + y VO9 + z obtained by the microwave‐assisted chemical insertion can be used in Al‐based rechargeable batteries.  相似文献   

16.
The development of cost‐effective and flexible electrodes is demanding in the field of energy storage. Herein, flexible FexOy/nitrogen‐doped carbon films (FexOy/NC‐MOG) are prepared by facile electrospinning of Fe‐based metal–organic gels (MOGs) followed by high‐temperature carbonization. This approach allows the even mixing of fragile coordination polymers with polyacrylonitrile into flexible films while reserving the structural characteristics of coordination polymers. After thermal treatment, FexOy/NC‐MOG films possess uniformly distributed FexOy nanoparticles and larger accessible surface areas than traditional FexOy‐NC films without MOG. Taking advantage of the unique structure, FexOy/NC‐MOG exhibits a superior rate performance (449.8 mA h g?1 at 5000 mA g–1) and long cycle life (629.3 mA h g–1 after 500 cycles at 1000 mA g–1) when used as additive‐free anodes in lithium‐ion batteries.  相似文献   

17.
Double halide perovskites are a class of promising semiconductors applied in photocatalysis, photovoltaic devices, and emitters to replace lead halide perovskites, owing to their nontoxicity and chemical stability. However, most double perovskites always exhibit low photoluminescence quantum efficiency (PLQE) due to the indirect bandgap structure or parity‐forbidden transition problem, limiting their further applications. Herein, the self‐trapped excitons emission of Cs2NaInCl6 by Sb‐doping, showing a blue emission with high PLQE of 84%, is improved. Further, Sb/Mn codoped Cs2NaInCl6 nanocrystals are successfully synthesized by the hot‐injection method, showing a tunable dual‐emission covering the white‐light spectrum. The studies of PL properties and dynamics reveal that an energy transfer process can occur between the self‐trapped excitons and dopants (Mn2+). The work provides a new perspective to design novel lead‐free double perovskites for realizing a unique white‐light emission.  相似文献   

18.
Mixed‐halide wide‐bandgap perovskites are key components for the development of high‐efficiency tandem structured devices. However, mixed‐halide perovskites usually suffer from phase‐impurity and high defect density issues, where the causes are still unclear. By using in situ photoluminescence (PL) spectroscopy, it is found that in methylammonium (MA+)‐based mixed‐halide perovskites, MAPb(I0.6Br0.4)3, the halide composition of the spin‐coated perovskite films is preferentially dominated by the bromide ions (Br?). Additional thermal energy is required to initiate the insertion of iodide ions (I?) to achieve the stoichiometric balance. Notably, by incorporating a small amount of formamidinium ions (FA+) in the precursor solution, it can effectively facilitate the I? coordination in the perovskite framework during the spin‐coating and improve the composition homogeneity of the initial small particles. The aggregation of these homogenous small particles is found to be essential to achieve uniform and high‐crystallinity perovskite film with high Br? content. As a result, high‐quality MA0.9FA0.1Pb(I0.6Br0.4)3 perovskite film with a bandgap (Eg) of 1.81 eV is achieved, along with an encouraging power‐conversion‐efficiency of 17.1% and open‐circuit voltage (Voc) of 1.21 V. This work also demonstrates the in situ PL can provide a direct observation of the dynamic of ion coordination during the perovskite crystallization.  相似文献   

19.
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 )Csx PbBr3 (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 )Csx PbBr3, 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 FA0.8Cs0.2PbBr3, 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.  相似文献   

20.
Fabrication of hierarchical nanosheet arrays of 1T phase of transition‐metal dichalcogenides is indeed a critical task, but it holds immense potential for energy storage. A single‐step strategy is employed for the fabrication of stable 1T‐MnxMo1–xS2–ySey and MoFe2S4–zSez hierarchical nanosheet arrays on carbon cloth as positive and negative electrodes, respectively. The flexible asymmetric supercapacitor constructed with these two electrodes exhibits an excellent electrochemical performance (energy density of ≈69 Wh kg?1 at a power density of 0.985 kW kg?1) with ultralong cyclic stability of ≈83.5% capacity retention, after 10 000 consecutive cycles. Co‐doping of the metal and nonmetal boosts the charge storage ability of the transition‐metal chalcogenides following enrichment in the metallic 1T phase, improvement in the surface area, and expansion in the interlayer spacing in tandem, which is the key focus of the present study. This study explicitly demonstrates the exponential enhancement of specific capacity of MoS2 following intercalation and doping of Mn and Se, and Fe2S3 following doping of Mo and Se could be an ideal direction for the fabrication of novel energy‐storage materials with high‐energy storage ability.  相似文献   

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