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1.
Adv Mater ; 32(4): e1906374, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31799762

RESUMO

An efficient electron transport layer (ETL) plays a key role in promoting carrier separation and electron extraction in planar perovskite solar cells (PSCs). An effective composite ETL is fabricated using carboxylic-acid- and hydroxyl-rich red-carbon quantum dots (RCQs) to dope low-temperature solution-processed SnO2 , which dramatically increases its electron mobility by ≈20 times from 9.32 × 10-4 to 1.73 × 10-2 cm2 V-1 s-1 . The mobility achieved is one of the highest reported electron mobilities for modified SnO2 . Fabricated planar PSCs based on this novel SnO2 ETL demonstrate an outstanding improvement in efficiency from 19.15% for PSCs without RCQs up to 22.77% and have enhanced long-term stability against humidity, preserving over 95% of the initial efficiency after 1000 h under 40-60% humidity at 25 °C. These significant achievements are solely attributed to the excellent electron mobility of the novel ETL, which is also proven to help the passivation of traps/defects at the ETL/perovskite interface and to promote the formation of highly crystallized perovskite, with an enhanced phase purity and uniformity over a large area. These results demonstrate that inexpensive RCQs are simple but excellent additives for producing efficient ETLs in stable high-performance PSCs as well as other perovskite-based optoelectronics.

2.
ACS Appl Mater Interfaces ; 12(1): 836-843, 2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31840488

RESUMO

Perovskite solar cells have attracted worldwide attention as one of the key research areas in the field of thin-film photovoltaics. Although they exhibit easy solution processability, it is important to effectively control the crystallization of the light-absorbing layer, which affects the performance and stability of devices. Here, we present lead oxalate (PbC2O4) as a nonhalide lead constituent of the perovskite precursor solution, which contributes to anion replacement during thin film annealing. This strategy limits the perovskite nucleation rate and retards crystallization. As a result, we achieved excellent perovskite films with larger grains and fewer defects. The open-circuit voltage of the optimal device under 1 sun illumination rose to 1.12 V with a power conversion efficiency (PCE) of 20.20%. In addition, the indoor PCE at 1000 lux can reach 34.86%. This nonhalide lead compound dopant provides a guide for the crystallization of perovskite materials and paves a way for the fabrication of nonhalide perovskite solar cells.

3.
Science ; 365(6453): 591-595, 2019 08 09.
Artigo em Inglês | MEDLINE | ID: mdl-31395783

RESUMO

Although ß-CsPbI3 has a bandgap favorable for application in tandem solar cells, depositing and stabilizing ß-CsPbI3 experimentally has remained a challenge. We obtained highly crystalline ß-CsPbI3 films with an extended spectral response and enhanced phase stability. Synchrotron-based x-ray scattering revealed the presence of highly oriented ß-CsPbI3 grains, and sensitive elemental analyses-including inductively coupled plasma mass spectrometry and time-of-flight secondary ion mass spectrometry-confirmed their all-inorganic composition. We further mitigated the effects of cracks and pinholes in the perovskite layer by surface treating with choline iodide, which increased the charge-carrier lifetime and improved the energy-level alignment between the ß-CsPbI3 absorber layer and carrier-selective contacts. The perovskite solar cells made from the treated material have highly reproducible and stable efficiencies reaching 18.4% under 45 ± 5°C ambient conditions.

4.
J Am Chem Soc ; 141(35): 13948-13953, 2019 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-31403287

RESUMO

Surface effects usually become negligible on the micrometer or sub-micrometer scale due to lower surface-to-bulk ratio compared to nanomaterials. In lead halide perovskites, however, their "soft" nature renders them highly responsive to the external field, allowing for extended depth scale affected by the surface. Herein, by taking advantage of this unique feature of perovskites we demonstrate a methodology for property manipulation of perovskite thin films based on secondary grain growth, where tuning of the surface induces the internal property evolution of the entire perovskite film. While in conventional microelectronic techniques secondary grain growth generally involves harsh conditions such as high temperature and straining, it is easily triggered in a perovskite thin film by a simple surface post-treatment, producing enlarged grain sizes of up to 4 µm. The resulting photovoltaic devices exhibit significantly enhanced power conversion efficiency and operational stability over a course of 1000 h and an ambient shelf stability of over 4000 h while maintaining over 90% of its original efficiency.

5.
ACS Omega ; 4(2): 4304-4311, 2019 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-31459635

RESUMO

Owing to the inhomogeneous distribution of FLiNaK salt impregnated into graphite which is observed by scanning electron microscopy and an element probe micro-analyzer, a map scan of in situ real-time tensile synchrotron-based two-dimensional X-ray diffraction (2D-XRD) at several fixed external forces was implemented to reveal the local microstructure evolution of graphite and FLiNaK salt. Notably, a stress concentration area (SCA), that is, the main interaction area between graphite and salt, was found and then transformed from one region to another region because of the unbalanced squeeze interaction between graphite and FLiNaK salt with the increase of external force. During the external stress load process, a smaller grain size, poorer crystallinity of graphite and a larger grain size, better crystallinity of FLiNaK salt appear in the SCA; meanwhile, the changes of crystallographic preferred orientation of FLiNaK salt domains in SCA imply that the external load force makes better the ordered stacking of the larger crystal grains of the FLiNaK salt impregnated into graphite. Most importantly, we have found for the first time that the fracture position of graphite impregnated with FLiNaK salt always occurs near the SCA rather than at a fixed region under the external stress load. Thus, the present study not only helps to reveal the interaction mechanism between graphite and FLiNaK salt under the external stress load but also contributes to accurately predict and analyze the stress state of components, which would have an effective impact on the design of a molten salt reactor and the reliability of the component safety assessment.

6.
J Phys Chem Lett ; 10(15): 4422-4428, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31318215

RESUMO

Fundamental understanding on the spin transport properties of semiconducting organic-inorganic hybrid perovskites (OIHP) is of great importance for advancing their applications for spin-optoelectronic devices. Herein, the study of spin-pumping induced inverse spin Hall effect in Ni80Fe20(Py)/CH3NH3PbCl3-xIx/Pt trilayers with different OIHP spacer thicknesses concludes the spin diffusion length in CH3NH3PbCl3-xIx as large as 61 ± 7 nm at room temperature. In addition, spin-valves with a structure of Ni80Fe20(Py)/CH3NH3PbCl3-xIx/AlOx/Co was fabricated as well. Using a ∼160 nm-thick CH3NH3PbCl3-xIx spacer, the present spin valve exhibits a positive magnetoresistance (MR) of 0.57% at 10 K. Thus, the present spin related results demonstrate that electrical spin-polarized carrier injection, transport, and detection, which are essential in spintronic devices, can be successfully established in OIHP films. The outstanding spin transport in the present CH3NH3PbCl3-xIx should be owing to its highly out-of-plane oriented crystalline texture and Rashba spin splitting at domain boundaries between crystallographic orientations. These results demonstrate OIHP as very attractive materials for spintronics.

7.
Adv Mater ; 31(25): e1901519, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31069886

RESUMO

Halide perovskite films processed from solution at low-temperature offer promising opportunities to make flexible solar cells. However, the brittleness of perovskite films is an issue for mechanical stability in flexible devices. Herein, photo-crosslinked [6,6]-phenylC61 -butyric oxetane dendron ester (C-PCBOD) is used to improve the mechanical stability of methylammonium lead iodide (MAPbI3 ) perovskite films. Also, it is demonstrated that C-PCBOD passivates the grain boundaries, which reduces the formation of trap states and enhances the environmental stability of MAPbI3 . Thus, MAPbI3 perovskite solar cells are prepared on solid and flexible substrates with record efficiencies of 20.4% and 18.1%, respectively, which are among the highest ever reported for MAPbI3 on both flexible and solid substrates. The result of this work provides a step improvement toward stable and efficient flexible perovskite solar cells.

8.
J Phys Chem Lett ; 10(10): 2349-2356, 2019 May 16.
Artigo em Inglês | MEDLINE | ID: mdl-31007024

RESUMO

Reduced-dimensional (RD) perovskite solar cells (PSCs) are emerging as highly attractive alternatives to three-dimensional (3D) PSCs due to their dramatically improved environmental stability and photostability. Diamine-based RD perovskites with a single organic amine interlayer possess orderly inorganic sheets and a smaller insulation area, indicating great potential in combining high efficiency and long-term stability. Here, we report an efficient and stable RD PSC based on 1,4-butanediamine (BDA). We found that the BDA-based RD perovskite exhibits improved crystallinity, reduced trap-state densities, and enhanced charge mobility compared to those of butylamine (BA)-based RD (BA-RD) perovskite. A high power conversion efficiency of 17.91% was achieved with negligible hysteresis. Moreover, the device showed improved stability compared to those of BA-RD and 3D films and devices. The findings may inspire new developments in introducing organic diamine for efficient and stable RD PSCs.

9.
Nat Commun ; 10(1): 962, 2019 02 22.
Artigo em Inglês | MEDLINE | ID: mdl-30796250

RESUMO

The original version of this Article contained an error in the spelling of the author Dan Credgington, which was incorrectly given as Dan Credington. This has now been corrected in both the PDF and HTML versions of the Article.

10.
Nat Commun ; 10(1): 756, 2019 02 14.
Artigo em Inglês | MEDLINE | ID: mdl-30765699

RESUMO

Owing to strong light-matter interaction, two-dimensional (2D) organic crystal is regarded as promising materials for ultrasensitive photodetectors, however it still received limited success due to degraded photoelectrical response and problems in controllable growth. Here, we find the growth of 2D organic crystal obeys Gibbs-Curie-Wulff law, and develop a seed-epitaxial drop-casting method to grow millimeter-sized 1,4-bis(4-methylstyryl)benzene 2D crystals on SiO2/Si in a thermodynamically controlled process. On SiO2/Si, a distinct 2D limit effect is observed, which remarkably enhances internal photoresponsivity compared with bulk crystals. Experiment and calculation show the molecules stack more compactly at the 2D limit, thus better molecular orbital overlap and corresponding changes in the band structure lead to efficient separation and transfer of photo-generated carriers as well as enhanced photo-gating modulation. This work provides a general insight into the growth and the dimension effect of the 2D organic crystal, which is valuable for the application in high-performance photoelectrical devices.

11.
ACS Nano ; 13(2): 1645-1654, 2019 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-30604954

RESUMO

Two-dimensional (2D) lead halide perovskites with long-chain ammonium halides display high photoluminescence quantum yields (PLQYs), because of their size and dielectric confinement, which hold promise for a high-efficiency and low-cost light-emitting diode (LED). However, the presence of an insulating organic long-chain spacer cation (L) dramatically deteriorates the charge transport properties along the out-of-plane nanoplatelet direction or adjacent nanocrystals, which would limit the device performance of the LED. To overcome this issue, we successfully incorporate small alkaline ions such as sodium (Na+) to replace the long organic molecule. Grazing incidence X-ray diffraction measurements verify 2D layer formation with a preferred crystallite orientation. In addition, the incorporated sodium salt also generates amorphous sodium lead bromide (NaPbBr3) in perovskite as spacers to form a nanocrystal-like halide perovskite film. The PLQY is dramatically improved in the sodium-incorporated film because of its enhanced photoluminescence lifetime. Upon incorporation of a low concentration of an organic additive, this two-dimensional-three-dimensional (2D-3D) perovskite can achieve a compact and uniform film. Therefore, a 2D-3D perovskite achieves a high external quantum efficiency of 15.9% with good operational stability. We develop a type of 2D-3D halide perovskite with various inorganic ions as spacers for promising high-performance optoelectronic devices.

12.
Nanoscale ; 10(41): 19322-19329, 2018 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-30324959

RESUMO

Light-emitting diodes (LEDs) based on two-dimensional (2D) perovskite nanoplatelets exhibit high electroluminescence (EL) efficiency because of the quantum confinement effect, which increases electron-hole recombination to promote radiative emission. It is well-known that a 2D nanoplatelet structure (〈n〉 = 1) is detrimental for luminescence efficiency due to possible thermal quenching of excitons at room temperature. Here, a simple strategy is developed to suppress growth of NMA2PbBr4 (〈n〉 = 1) nanoplatelets by carefully tuning the precursor ratio of cesium bromide (CsBr), formamidinium bromide (FABr) and 1-naphthylmethylammonium bromide (NMABr). The sub-domain size of the perovskite crystal decreases as the long-chain ligand NMABr ratio increases, leading to enhanced photoluminescence quantum yields (PLQY) due to size confinement effect when the NMABr ratio is below 60%. Unfortunately, the NMA2PbBr4 component in 2D/3D perovskites also grows with increasing NMABr ratio, which results in poor EL efficiency. FABr incorporation can provide additional control over suppression of NMA2PbBr4 growth in 2D/3D perovskites. A compact and uniform perovskite film with reduced NMA2PbBr4 content achieves PLQY of ∼61%. Benefiting from these features, a green perovskite LED yields current efficiency of 46.8 cd A-1 with an external quantum efficiency of 14.9%. This study paves a new way to modulate the crystal structure in perovskites via a simple and effective method for high-performance LEDs.

13.
Nat Commun ; 9(1): 3892, 2018 09 24.
Artigo em Inglês | MEDLINE | ID: mdl-30250032

RESUMO

Organometal halide perovskites (OHP) are promising materials for low-cost, high-efficiency light-emitting diodes. In films with a distribution of two-dimensional OHP nanosheets and small three-dimensional nanocrystals, an energy funnel can be realized that concentrates the excitations in highly efficient radiative recombination centers. However, this energy funnel is likely to contain inefficient pathways as the size distribution of nanocrystals, the phase separation between the OHP and the organic phase. Here, we demonstrate that the OHP crystallite distribution and phase separation can be precisely controlled by adding a molecule that suppresses crystallization of the organic phase. We use these improved material properties to achieve OHP light-emitting diodes with an external quantum efficiency of 15.5%. Our results demonstrate that through the addition of judiciously selected molecular additives, sufficient carrier confinement with first-order recombination characteristics, and efficient suppression of non-radiative recombination can be achieved while retaining efficient charge transport characteristics.

14.
ACS Appl Mater Interfaces ; 10(28): 24320-24326, 2018 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-29926721

RESUMO

Solution-processed perovskite light-emitting diodes (LEDs) have attracted wide attention in the past several years. However, the overall efficiency and stability of perovskite-based LEDs remain inferior to those of organic or quantum dot LEDs. Nonradiative charge recombination and the unbalanced charge injection are two critical factors that limit the device efficiency and operational stability of perovskite LEDs. Here, we develop a strategy to modify the interface between the hole transport layer and the perovskite emissive layer with an amphiphilic conjugated polymer of poly[(9,9-bis(3'-( N, N-dimethylamino)propyl)-2,7-fluorene)- alt-2,7-(9,9-dioctylfluorene)] (PFN). We show evidences that PFN improves the quality of the perovskite film, which effectively suppresses nonradiative recombination. By further improving the charge injection balance rate, a green perovskite LED with a champion current efficiency of 45.2 cd/A, corresponding to an external quantum efficiency of 14.4%, is achieved. In addition, the device based on the PFN layer exhibits improved operational lifetime. Our work paves a facile way for the development of efficient and stable perovskite LEDs.

15.
Adv Mater ; 30(20): e1800258, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29603445

RESUMO

Exploiting organic/inorganic hybrid perovskite solar cells (PSCs) with reduced Pb content is very important for developing environment-friendly photovoltaics. Utilizing of Pb-Sn alloying perovskite is considered as an efficient route to reduce the risk of ecosystem pollution. However, the trade-off between device performance and Sn substitution ratio due to the instability of Sn2+ is a current dilemma. Here, for the first time, the highly efficient Pb-Sn-Cu ternary PSCs are reported by partial replacing of PbI2 with SnI2 and CuBr2 . Sn2+ substitution results in a redshift of the absorption onset, whereas worsens the film quality. Interestingly, Cu2+ introduction can passivate the trap sites at the crystal boundaries of Pb-Sn perovskites effectively. Consequently, a power conversion efficiency as high as 21.08% in inverted planar Pb-Sn-Cu ternary PSCs is approached. The finding opens a new route toward the fabrication of high efficiency Pb-Sn alloying perovskite solar cells by Cu2+ passivation.

16.
Sci Rep ; 7(1): 10673, 2017 09 06.
Artigo em Inglês | MEDLINE | ID: mdl-28878406

RESUMO

An in-situ real-time synchrotron-based grazing incidence X-ray diffraction was systematically used to investigate the crystal structural evolution of carbon fiber reinforced carbon matrix (C/C) composite impregnated with FLiNaK molten salt during the heat-treatment process. It was found that the crystallographic thermal expansion and contraction rate of interlayer spacing d 002 in C/C composite with FLiNaK salt impregnation is smaller than that in the virgin sample, indicating the suppression on interlayer spacing from FLiNaK salt impregnated. Meanwhile the crystallite size L C002 of C/C composite with FLiNaK salt impregnation is larger than the virgin one after whole heat treatment process, indicating that FLiNaK salt impregnation could facilitate the crystallization of C/C composite after heat treatment process. This improved crystallization in C/C composite with FLiNaK salt impregnation suggests the synthetic action of the salt squeeze effect on crooked carbon layer and the release of internal residual stress after heating-cooling process. Thus, the present study not only contribute to reveal the interaction mechanism between C/C composite and FLiNaK salt in high temperature environment, but also promote the design of safer and more reliable C/C composite materials for the next generation molten salt reactor.

17.
ACS Appl Mater Interfaces ; 9(27): 23141-23151, 2017 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-28603955

RESUMO

Despite rapid successful developments toward promising perovskite solar cells (PSCs) efficiency, they often suffer significant hysteresis effects. Using synchrotron-based grazing incidence X-ray diffraction (GIXRD) with different probing depths by varying the incident angle, we found that the perovskite films consist of dual phases with a parent phase dominant in the interior and a child phase with a smaller (110) interplanar space (d(110)) after rapid thermal annealing (RTA), which is a widely used post treatment to improve the crystallization of solution-processed perovskite films for high-performance planar PSCs. In particular, the child phase composition gradually increases with decreasing depth till it becomes the majority on the surface, which might be one of the key factors related to hysteresis in fabricated PSCs. We further improve the crystalline phase purity of the solution-processed CH3NH3PbI3-xClx perovskite film (referred as g-perovskite) by using a facile gradient thermal annealing (GTA), which shows a uniformly distributed phase structure in pinhole-free morphology with less undercoordinated Pb and I ions determined by synchrotron-based GIXRD, grazing incidence small-angle X-ray scattering, scanning electron microscopy, and X-ray photoelectron spectroscopy. Regardless of device structures (conventional and inverted types), the planar heterojunction PSCs employing CH3NH3PbI3-xClx g-perovskite films exhibit negligible hysteresis with a champion power conversion efficiency of 17.04% for TiO2-based conventional planar PSCs and 14.83% for poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate) (PEDOT:PSS)-based inverted planar PSCs. Our results indicate that the crystalline phase purity in CH3NH3PbI3-xClx perovskite film, especially in the surface region, plays a crucial role in determining the hysteresis effect and device performance.

18.
Sci Rep ; 7: 46724, 2017 04 21.
Artigo em Inglês | MEDLINE | ID: mdl-28429762

RESUMO

Using poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as hole conductor, a series of inverted planar CH3NH3PbI3-xClx perovskite solar cells (PSCs) were fabricated based on perovskite annealed by an improved time-temperature dependent (TTD) procedure in a flowing nitrogen atmosphere for different time. Only after an optimum annealing time, an optimized power conversion efficiency of 14.36% could be achieved. To understand their performance dependence on annealing time, an in situ real-time synchrotron-based grazing incidence X-ray diffraction (GIXRD) was used to monitor a step-by-step gradual structure transformation from distinct mainly organic-inorganic hybrid materials into highly ordered CH3NH3PbI3 crystal during annealing. However, a re-crystallization process of perovskite crystal was observed for the first time during such an annealing procedure, which helps to enhance the perovskite crystallization and preferential orientations. The present GIXRD findings could well explain the drops of the open circuit voltage (Voc) and the fill factor (FF) during the ramping of temperature as well as the optimized power conversion efficiency achieved after an optimum annealing time. Thus, the present study not only illustrates clearly the decisive roles of post-annealing in the formation of solution-processed perovskite to better understand its formation mechanism, but also demonstrates the crucial dependences of device performance on the perovskite microstructure in PSCs.

19.
ACS Appl Mater Interfaces ; 9(15): 13240-13246, 2017 Apr 19.
Artigo em Inglês | MEDLINE | ID: mdl-28332402

RESUMO

Effective and stable hole-transporting materials (HTMs) are necessary for obtaining excellent planar perovskite solar cells (PSCs). Herein, we reported a solution-processed composite HTM consisting of a polymer poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and a small-molecule copper phthalocyanine-3,4',4″,4‴-tetrasulfonated acid tetrasodium salt (TS-CuPc) with optimized doping ratios. The composite HTM is crucial for not only enhancing the hole transport and extraction but also improving the perovskite crystallization. In addition, the composite HTM can weaken the indium tin oxide erosion by reducing the acidity and increasing the dispersibility of the PEDOT:PSS aqueous dispersion via incorporating suitable TS-CuPc. Consequently, a highly efficient device was fabricated with a power conversion efficiency (PCE) of 17.29%. Its short-circuit current (JSC) is 22.23 mA/cm2, and its open-circuit voltage (VOC) is 1.01 V. Meanwhile, it exhibited a higher fill factor (FF) of 77% and improved cell stability. The developed composite HTM provides a good potential anode interfacial layer for fabricating outstanding PSCs.

20.
Phys Chem Chem Phys ; 19(9): 6546-6553, 2017 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-28197568

RESUMO

The electronic structures of rubrene films deposited on CH3NH3PbI3 perovskite have been investigated using in situ ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It was found that rubrene molecules interacted weakly with the perovskite substrate. Due to charge redistribution at their interface, a downward 'band bending'-like energy shift of ∼0.3 eV and an upward band bending of ∼0.1 eV were identified at the upper rubrene side and the CH3NH3PbI3 substrate side, respectively. After the energy level alignment was established at the rubrene/CH3NH3PbI3 interface, its highest occupied molecular orbital (HOMO)-valence band maximum (VBM) offset was found to be as low as ∼0.1 eV favoring the hole extraction with its lowest unoccupied molecular orbital (LUMO)-conduction band minimum (CBM) offset as large as ∼1.4 eV effectively blocking the undesired electron transfer from perovskite to rubrene. As a demonstration, simple inverted planar solar cell devices incorporating rubrene and rubrene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layers (HTLs) were fabricated in this work and yielded a champion power conversion efficiency of 8.76% and 13.52%, respectively. Thus, the present work suggests that a rubrene thin film could serve as a promising hole transport layer for efficient perovskite-based solar cells.

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