Figure 5. Photovoltaic device structure and performance. SEM images of A) top-view and B) cross-sectional Sb 2 Se 3 fi lm deposited on top of TiO 2 buffer. The thicknesses of v and Sb 2 Se 3 were about 100 nm and 580 nm, respectively. C) Schematic confi guration of TiO 2 /Sb 2 Se 3 heterojunction device. D) J -V curves of Sb 2 Se 3 solar cell performance in the dark and under 100 mW cm −2 simulated AM1.5G irradiation, respectively, and the performance of the device baked at 60 °C for 24 h. The inset shows an the image of our device.

Two-dimensional atomic crystals, such as two-dimensional oxides, have attracted much attention in energy storage because nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. However, current strategies are largely limited to intrinsically layered compounds. Here we report a general strategy that uses the surfaces of water-soluble salt crystals as growth templates and is applicable to not only layered compounds but also various transition metal oxides, such as hexagonal-MoO3, MoO2, MnO and hexagonal-WO3. The planar growth is hypothesized to occur via a match between the crystal lattices of the salt and the growing oxide. Restacked two-dimensional hexagonal-MoO3 exhibits high pseudocapacitive performances (for example, 300 F cm−3 in an Al2(SO4)3 electrolyte). The synthesis of various two-dimensional transition metal oxides and the demonstration of high capacitance are expected to enable fundamental studies of dimensionality effects on their properties and facilitate their use in energy storage and other applications.

Recently, CuSbS 2 has been proposed as an alternative earth-abundant absorber material for thin film solar cells. However, no systematic study on the chemical, optical, and electrical properties of CuSbS 2 has been reported. Using density functional theory (DFT) calculations, we showed that CuSbS 2 has superior defect physics with extremely low concentration of recombination-center defects within the forbidden gap, espeically under the S rich condition. It has intrinsically p-type conductivity, which is determined by the dominant Cu vacancy (V Cu ) defects with the a shallow ionization level and the lowest formation energy. Using a hydrazine based solution process, phase-pure, highly crystalline CuSbS 2 film with large grain size was successfully obtained. Optical absorption investigation revealed that our CuSbS 2 has a direct band gap of 1.4 eV. Ultraviolet photoelectron spectroscopy (UPS) study showed that the conduction band and valence band are located at 3.85 eV and −5.25 eV relative to the vacuum level, respectively. As the calculations predicted, a p-type conductivity is observed in the Hall effect measurements with a hole concentration of ∼10 18 cm −3 and hole mobility of 49 cm 2 /(V s). Finally, we have built a prototype FTO/CuSbS 2 /CdS/ZnO/ZnO:Al/Au solar cell and achieved 0.50% solar conversion efficiency. Our theoretical and experimental investigation confirmed that CuSbS 2 is indeed a very promising absorber material for solar cell application.

The new emerging organometal trihalide perovskite holds great potential for high-efficiency, low-cost solar cells because of its high solar to electricity conversation efficiency (>16%) achieved within 4 years of research and its low-temperature solution processing. In this Letter we introduce NiO as the hole-collecting and -conducting layer in perovskite solar cells. Through a modified sequential deposition strategy, we successfully fabricated high-quality CH 3 NH 3 PbI 3 onto a planar NiO layer and built a planar inverted ITO/NiO/CH 3 NH 3 PbI 3 / PCBM/Al photovoltaic device. A device efficiency of 7.6% was achieved with an impressively high open-circuit voltage (V oc ) of 1.05 V. Our study demonstrates the potential application of a deep work function NiO layer for perovskite solar cells.H igh-efficiency, low-cost solar cells are the everlasting pursuit of photovoltaic research. Very recently, organometal halide perovskite has attracted tremendous research attention because of its potential to realize this goal. First introduced in 2009 by Miyasaka's group as the sensitizer for dye-sensitized solar cells (DSSCs) using liquid electrolyte, 1 organometal halide perovskites gradually evolved to solid-state DSSCs by incorporating triarylamine derivative 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-MeOTAD) 2 or other materials 3,4 as the hole-transporting and -collecting layer and finally developed into the current form of a planar p−i−n heterojunction device configuration. 5,6 State-of-the-art perovskite solar cells include sequentially deposited CH 3 NH 3 PbI 3 to sensitize a mesoporous TiO 2 electrode and achieved 14.1% certified device efficiency 7 and also include a thermally evaporated CH 3 NH 3 PbI 3−x Cl x absorber to build 15.4% planar heterojunction solar cells. 5 This soaring conversion efficiency, coupled with their simple device fabrication process, enables the perovskite solar cell to be a very promising candidate for high-efficiency, low-cost photovoltaics. 8,9 Similar to other absorber materials in solar cells, organometal trihalide perovskite is capable of efficient and balanced electron and hole transport. Diffusion lengths of more than 100 nm for C H 3 N H 3 P b I 3 1 0 a n d m o r e t h a n 1 0 0 0 n m f o r CH 3 NH 3 PbI 3−x Cl x 11 were reported from a femtosecond transient optical spectroscopy study and transient absorption and photoluminescence-quenching measurements, respectively. As a result, planar heterojunction device configurations are gradually attracting more attention because removal of the mesoscopic layer simplifies device preparation and reduces materials cost. Many planar device architectures, such as TiO 2 / perovskite/spiro-MeOTAD, 5 PEDOT:PSS/perovskite/C 60 , 12,13 and ZnO/perovskite/spiro-MeOTAD, 6 were reported, with the best efficiency achieving 15.7%, 13 competing favorably with perovskite solar cells employing mesoscopic layers. One additional benefit, not yet fully demonstrated in perovskite solar cells but widely accepted in traditional t...

2D materials, particularly those bearing in-plane anisotropic optical and electrical properties such as black phosphorus and ReS , have spurred great research interest very recently as promising building blocks for future electronics. However, current progress is limited to layered compounds that feature atomic arrangement asymmetry within the covalently bonded planes. Herein, a series of highly anisotropic nanosheets (Sb Se , Sb S , Bi S , and Sb (S, Se) ), which are composed of 1D covalently linked ribbons stacked together via van der Waals force, is introduced as a new member to the anisotropic 2D material family. These unique anisotropic nanosheets are successfully fabricated from their polymer-like bulk counterparts through a gentle water freezing-thawing approach. Angle-resolved polarized Raman spectroscopy characterization confirms the strong in-plane asymmetry of Sb Se nanosheets, and photodetection study reveals their high responsivity and anisotropic in-plane transport. This work can enlighten the synthesis and application of new anisotropic 2D nanosheets that can be potentially applied for future electronic and optoelectronic devices.

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and thus abundant PL emissions covering ultraviolet, visible light, as well as infrared region. [11,12] In addition, the FWHM could even reach 10 nm, enabling high color purity and serving as phosphors in display, biolabeling, etc. [13,14] Recently, some reports demonstrated that colloidal CsPbX 3 NCs with Mn 2+ doping exhibited dual-color emission, validating the facile doping in perovskites due to their nonrigid structures. [15][16][17] Manganese (Mn) ions were incorporated into CsPbX 3 NCs, exhibiting a dramatic effect on relative intensities of intrinsic band-edge emission and Mn ion emission, which was ascribed to the influence of energy transfer between the Mn ion and the semiconductor host. Subsequently, Sn 2+ , Cd 2+ , and Zn 2+ are found to partially replace Pb 2+ cations in colloidal CsPbBr 3 NCs by the method of cation exchange and lead to a blueshift of the optical spectra, while maintaining the high photoluminescence quantum yields (>50%) and narrow emission of the parent NCs. [18] However, as far as we are concerned, there is still no report about RE ion doping in lead halide perovskite NCs.In the present work, we successfully doped the RE ions Eu 3+ and Tb 3+ into CsPbBr 3 NCs through one-pot ultrasonication. The ultrasonic method has been proven a successful route for nanocrystal synthesis. [19][20][21] During the ultrasonication, acoustic cavitation could create bubbles, with the temperature of hot spots reaching above 5000 K and the pressure exceeding 1000 bar, and hence accumulate intensive energy inside. [22] Collapse of these bubbles supplies a transient ultrahigh energy to overcome the nucleation barrier and initiates the growth of NCs simultaneously. [23] Here, we believe that the ultrasonication could not only provide energy for the synthesis of our CsPbBr 3 NCs, but also facilitate the incorporation of RE dopants into the NC lattices. We thus developed a one-pot strategy to synthesize RE ion-doped halide perovskite NCs, and the synthetic process is schematically shown in Figure 1. Briefly, CsBr and PbBr 2 powder was loaded into N,N-Dimethylformamide (DMF) solution containing a proper amount of RE ions, and then the solution was subjected to ultrasonication with the assistance of water cooling. RE ion-doped CsPbBr 3 NCs were collected after centrifugation and other processes. The detailed procedure was documented in the Experimental Section. Such method has a relatively low yield (around 4.32%), and we can always find the undissolved precursors (CsBr, PbBr 2 ) in the bottom. These undissolved precursors can be reused for another sonication cycle to enable high utilization efficiency.The products were first characterized by transmission electron microscope (TEM) images, as shown in Figure 2a-c. The nondoped and doped NCs exhibited cubic shapes with different levels of aggregate and slight truncations caused by the ultrasonication synthesis procedure. The average sizes of CsPbBr 3 , CsPbBr 3 :Eu 3+ ,

Sb2(S1−xSex)3 (0 ≤ x ≤ 1) compounds have been proposed as promising light-absorbing materials for photovoltaic device applications. However, no systematic study on the synthesis and characterization of polycrystalline Sb2(S1−xSex)3 thin films has been reported. Here, using a hydrazine based solution process, single-phase Sb2(S1−xSex)3 films were successfully obtained. Through Raman spectroscopy, we have investigated the dissolution mechanism of Sb in hydrazine: 1) the reaction between Sb and S/Se yields [Sb4S7]2-/[Sb4Se7]2- ions within their respective solutions; 2) in the Sb-S-Se precursor solutions, Sb, S, and Se were mixed on a molecular level, facilitating the formation of highly uniform polycrystalline Sb2(S1−xSex)3 thin films at a relatively low temperature. UV-vis-NIR transmission spectroscopy revealed that the band gap of Sb2(S1−xSex)3 alloy films had a quadratical relationship with the Se concentration x and it followed the equation , where the bowing parameter was 0.118 eV. Our study provides a valuable guidance for the adjustment and optimization of the band gap in hydrazine solution processed Sb2(S1−xSex)3 alloy films for the future fabrication of improved photovoltaic devices.