It is very significant to understand the formation of perovskite crystals from the precursor solution and construct high-quality films to achieve highly efficient perovskite solar cells (PSCs). Here, we have revealed a colloidal strategy to prepare compact monolayer perovskite films by controlling the size of colloidal clusters in the perovskite precursor. Under the action of the coordination interaction, the introduction of CH3NH3Cl (MACl) into the standard perovskite precursor significantly increases the size of colloidal clusters. Meanwhile, N-dimethyl sulfoxide (DMSO) is further employed to stabilize the characteristics of the colloidal clusters and improve the reproducibility of the anti-solvent method. The large colloidal clusters can be orderly arranged on the substrate by spin-coating to form intermediate phase monolayer films, which grow to form large grains with an average size of 3 μm. Due to the much lower trap-state density and higher crystallinity of the monolayer perovskite films, a power conversion efficiency (PCE) of 19.14% has been achieved. This study sheds light on the conversion mechanism of perovskite crystals from the colloidal precursor to solid films, and paves the way for further improvement of high-quality perovskite films that can lead to high performance devices.

A hybrid organic/inorganic heterojunction structured photodetector has attracted much attention due to its high device stability and ease of fabrication. In this work, an ultraviolet photodetector with the configuration of spiro-OMeTAD/mesoporous TiO2/compact TiO2 was developed. The small molecule of spiro-OMeTAD was introduced as the active layer, owing to its fast response to the ultraviolet light and high glass transition temperature (Tg). The mesoporous TiO2 layer with a large specific area could accelerate the interface separation of electrons and holes, while the compact TiO2 layer was used to block the charge leakage between FTO and spiro-OMeTAD. With a 100 nm TiO2 mesoporous layer, the photodetector displayed a fast response time (<0.02 s), a low dark current density (8.79 nA cm−2) and a high detectivity (3.5 × 1013 Jones) at 340 nm light wavelength and a 0.60 V voltage output. Besides, the unencapsulated device in air also showed excellent long-term stability (∼2 months) and thermal stability (∼100 °C).

The synthesis and growth of perovskite films with controlled crystallinity and microstructure for highly efficient and stable solar cells is a critical issue. In this work, thiourea is introduced into the CH3NH3PbI3 precursor with two-step sequential ethyl acetate (EA) interfacial processing. This is shown for the first time to grow compact microsized and monolithically grained perovskite films. X-ray diffraction patterns and infrared spectroscopy are used to prove that thiourea significantly impacts the perovskite crystallinity and morphology by forming the intermediate phase MAI·PbI2·SC(NH2)2. Afterward, the residual thiourea which coursed charge recombination is completely extracted by the sequential EA processing. The product has improved light harvesting, suppressed defect state, and enhanced charge separation and transport. The sequentially EA processed perovskite solar cells offer an impressive 18.46% power conversion efficiency and excellent stability in ambient air. More importantly, the EA postprocessed perovskite solar cells also have excellent voltage response under ultraweak light (0.05% sun) with promising utility in photodetectors and photoelectric sensors.

The monolithic perovskite films with a single crystal cross profile are considered to be the ideal active layer for high efficiency perovskite solar cells (PSCs) owing to the minimization of defects and the maximization of charge carrier mobility. To date, how to prepare a high-quality monolithic perovskite film is still a challenge for PSCs. Here, we demonstrated a combined method via CH3NH3Cl (MACl) coordination and a heat assisted process (HAP) to grow a compact monolithic CH3NH3PbI3 (MAPbI3) film with an average grain size of 3.6 μm. The ordered intermediate phase framework of MAPbIxCly grew up from the bottom to the top on the heated substrate, avoiding the grain boundaries and pin-holes in the cross profile. According to the space charge limited current (SCLC), the trap density in the monolithic film was nearly an order of magnitude lower than that of the control samples, while the charge carrier mobility increased to 22.74 cm2 V−1 S−1, approaching that of the MAPbI3 single crystal. As a result, the power conversion efficiency (PCE) of the PSCs is increased from 13.26% to 18.34%. These results shed light on the preparation of high quality monolithic MAPbI3 films via retarding crystallization (MACl additive) and increasing the nucleation rate (HAP).

Copper selenide (CuxSe) has great potential as counter electrode for quantum dots sensitized solar cell (QDSSC) due to its excellent electrocatalytic activity and lower charge transfer resistance. A novel ion exchange method has been utilized to fabricate Cu3Se2 nanosheets array counter electrode. CdS layer was first deposited by sputtering and used as a template to grow compact and uniform Cu3Se2 film in a typical chemical bath. The morphology and thickness of the Cu3Se2 nanosheets were controlled by the deposition time. The final products (2h-Cu3Se2) showed significantly improved electrochemical catalytic activity and carrier transport property, leading to a much increased power conversion efficiency (4.01%) when compared with the CuS counter electrode CdS/CdSe QDSSC (3.21%).硒化铜(CuxSe)凭借优良的电催化活性和较低的电荷转移电阻, 在量子点敏化太阳电池(QDSSC)对电极方面表现出了巨大的潜力. 本研究采用一种新的离子交换方法制备了Cu3Se2纳米片阵列. 通过溅射沉积CdS层作为模板, 在化学浴中生长出均匀和高覆盖度的Cu3Se2薄膜, Cu3Se2纳米片的形貌和厚度由沉积时间控制, 最终产物(2h-Cu3Se2)显著改善了电化学催化活性和载流子传输性能, 相比较于CuS为对电极的CdS / CdSe量子点敏化太阳能电池, 其光伏性能由3.21%提升至4.01%.

Two-step dipping is one of the popular low temperature solution methods to prepare organic–inorganic halide perovskite (CH3NH3PbI3) films for solar cells. However, pinholes in perovskite films fabricated by the static growth method (SGM) result in low power conversion efficiency (PCE) in the resulting solar cells. In this work, the static dipping process is changed into a dynamic dipping process by controlled stirring PbI2 substrates in CH3NH3I isopropanol solution. The dynamic growth method (DGM) produces more nuclei and decreases the pinholes during the nucleation and growth of perovskite crystals. The compact perovskite films with free pinholes are obtained by DGM, which present that the big perovskite particles with a size of 350 nm are surrounded by small perovskite particles with a size of 50 nm. The surface coverage of the perovskite film is up to nearly 100%. Such high quality perovskite film not only eliminated pinholes, resulting in reduced charge recombination of the solar cells, but also improves the light harvesting efficiency. As a result, the PCE of the perovskite solar cells is increased from 11% for SGM to 13% for DGM.Keywords: CH3NH3PbI3 film; dynamic growth; perovskite solar cells; surface coverage; two-step dipping process

Mn-doping into CdS quantum dots (QDs) has been demonstrated a useful way to enhance the power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs), the detailed systematic study is needed to get a better fundamental understanding. This work focuses on the study of the effects of Mn dopant on light harvesting, charge transfer, and charge collection of the solar cells. The results indicate that the Mn-doping into CdS QDs increases the light absorbance and extends the light absorption range, which results in the enhancement of the photo-generated current density. In addition, both the electron transport rate and the electron diffusion length are also increased with the introduction of Mn dopant. So the charge collection efficiency (ηcc) of the solar cell increases from 89.9% for CdS sample to 96.7% for Mn/CdS sample. As a result, the PCE of Mn/CdS QDSC reaches 3.29%, which is much higher than that of CdS QDSC (2.01%).

Perovskite solar cells are known to have a power conversion efficiency dependent on subtle variation in chemical composition and crystal and microstructures of materials, processing conditions, and device fabrication procedures and conditions. The present work demonstrates such strong dependence of power conversion efficiency on a TiO2 film made of the same sol with various aging time. A dense and conformal TiO2 film was prepared by sol-gel method, and the influences of its surface morphology and thickness on performance of perovskite solar cells have been investigated. The surface morphology and thickness of the TiO2 film were tuned by adjusting the aging time of sol, resulting in enhanced short-circuit current density and fill factor of the perovskite solar cells due to increased coverage and roughness of perovskite films, light refraction, and effective charge recombination blocking effect, which were verified by means of the light absorption spectra, photoluminescence of perovskite films with and without hole transport layer, cyclic voltammogram, and electrochemical impedance spectra. The cells with a dense and conformal TiO2 compact layer derived fromthe sol aged for 4 h exhibit a power conversion efficiency of 15.7%, 50% higher than the efficiency based on TiO2 layer derived from 0 h aging sol and 3 times of the efficiency with TiO2 layer made from 8 h aged sol.钙钛矿太阳电池的光伏性能有赖于对材料的化学组分、晶体以及微观结构的精细调控和对工艺条件和制备过程的控制. 本工作针对不同陈化时间的溶胶制备的TiO2致密层与太阳电池性能之间的关联性进行了研究. 研究中, 通过溶胶-凝胶法制备了致密、均匀的TiO2薄膜, 并研究了其表面形貌及厚度对钙钛矿太阳电池性能的影响. 通过调节溶胶的陈化时间可以实现对TiO2表面形貌和厚度的控制, 由于陈化后的溶胶会提高TiO2致密层的覆盖度, 粗糙度及光的折射率, 并有效阻挡电子的复合, 从而导致钙钛矿太阳电池中短路电流密度和填充因子提升. 钙钛矿薄膜的吸收光谱, 光致发光谱, TiO2薄膜的循环伏安测试及整个电池的交流阻抗谱的测试结果, 也进一步论证了该结论. 结果显示使用陈化时间为4 h的溶胶制备的钙钛矿电池获得了15.7%的能量转化效率, 比使用0 h陈化的溶胶制备的太阳电池效率高出50%, 是使用陈化时间为8 h的溶胶制备的太阳能电池效率的3倍.

•A new antisolvent method was developed to fabricate smooth and compact perovskite.•The possible reactions in the perovskite formation process were first elaborated.•High stability and repeatability photovoltaic devices were readily fabricated.•The ion migration was first detected by an ordinary impedance measurement.Antisolvent precipitation method has been one of the favored strategies to fabricate compact, smooth and uniform perovskite films for high efficiency solar cells due to its dramatically accelerated crystallization process. However, the excessively fast crystallization restricted the further improvement of the photovoltaic performance. In this work, we introduced CH3NH3Cl into the pristine CH3NH3PbI3 precursor for antisolvent precipitation at low temperature and fabricated high quality perovskite films with desired morphology, crystallinity and optical properties. The X-ray diffractometry and ultraviolent-visible spectroscopy provided ample evidence that CH3NH3Cl exerted significant impacts on the perovskite crystallization process by controlling the delivery speed of PbI2 from the intermediate phase CH3NH3PbI2Cl. The possible reactions in the perovskite formation process were first elaborated. The resultant solar cells demonstrated an average power conversion efficiency around 16.63% and a best efficiency at 17.22% under the standard light illumination condition. In addition, the ion migration was first detected in the perovskite solar cells by an ordinary impedance measurement.

TiO2 nanocrystals are widely used in photoanodes for quantum dot solar cells (QDSCs) owing to their chemical stability and suitable energy band structure. However, surface defects and grain boundaries of TiO2 nanocrystals photoanodes allow high surface charge recombination, which limits the performance of QDSCs. In this work, an ultrathin TiO2 layer is introduced to the surface of TiO2 photoanodes by atomic layer deposition (ALD). The ultrathin layer not only reduces the surface defects of TiO2 nanoparticles and strengthens the connection between adjacent nanoparticles to suppress the charge recombination for improving the electron collection efficiency (ηcc), but also increases the surface energy of photoanodes to load more quantum dots (QDs) for enhancing the light harvesting efficiency (LHE). As a result, the solar cell based on CdS/CdSe QDs with ALD treatment exhibits an efficiency of 5.07% that is much higher than that of the cells without modification (4.03%).TiO2纳米晶体具有稳定的化学性质和合适的能带结构, 因而被广泛应用在量子点太阳能电池的光阳极材料中. 但是, 其较多的表面缺陷 和颗粒边界引起的严重复合限制了电池效率. 本文利用原子层沉积法(ALD)在TiO2光阳极膜上沉积一层超薄TiO2层. 实验结果表明, 这层超 薄TiO2层不仅减少了表面缺陷, 改善了颗粒间的连接性, 阻止了复合的发生, 提高了电子收集效率, 而且通过表面能的提升, 量子点的吸附量 增加, 光捕获效率(LHE)也得以提高. 因此, 基于ALD修饰的TiO2膜制备的太阳能电池的效率达5.07%, 明显优于没有ALD 修饰的电池(4.03%).

Quantum dot sensitized solar cells (QDSCs) have attracted considerable attention recently and become promising candidates for realizing a cost-effective solar cell. The design and synthesis of quantum dots (QDs) for achieving high photoelectric performance is an urgent need imposed on scientists. Here, we have succeeded in designing a QDSC with a high efficiency η of 6.33% based on Cd0.8Mn0.2Se quantum dots by facile chemical bath deposition (CBD). The effects of Mn2+ ions on the physical, chemical, and photovoltaic properties of the QDSCs are investigated. The Mn2+ ions doped into QDs can increase the light harvesting to produce more excitons. In addition, the Mn2+ dopant also raises the conduction band of CdSe, accelerates the electron injection kinetics and reduces the charge recombination, improving the charge transfer and collection. The increase of the efficiencies of light-harvesting, charge-transfer and charge-collection results in the improvement of the quantum efficiency of the solar cells. The power conversion efficiency of the solar cell is increased to 6.33% (Voc = 0.58 V, Jsc = 19.15 mA cm−2, and FF = 0.57).

ZnO nanorods (NRs) and nanosheets (NSs) were fabricated by adjusting the growth orientation of ZnO crystals in the reaction solution, respectively. The thin ZnO NSs were slowly assembled on the surface of NRs to form a hierarchically structured NR–NS photoelectrode for constructing CdS/CdSe quantum-dot-sensitized solar cells (QDSCs). This hierarchical structure had two advantages in improving the power conversion efficiency (PCE) of the solar cells: (a) it increased the surface area and modified the surface profile of the ZnO NRs to aid in harvesting more quantum dots, which leads to a high short-current density (Jsc); (b) it facilitated transportation of the electrons in this compact structure to reduce the charge recombination, which led to enhancement of the open-circuit voltage (Voc) and fill factor (FF). As a result, the QDSC assembled with the hierarchical NR–NS photoelectrode exhibited a high PCE of 3.28%, which is twice as much as that of the NR photoelectrode (1.37%).Keywords: CdS/CdSe; nanorod; nanosheet; quantum-dot-sensitized solar cell; ZnO;

This work reported on a bilayer photoelectrode constructed by ZnO nanoparticle (NP) film and ZnO microsphere (MS) scattering layer for CdS/CdSe quantum dot cosensitized solar cells (QDSCs) with a power conversion efficiency (PCE) of greater than 5%. We controlled the growth orientations of ZnO crystals to form nanosheets, which attached together and assembled into MS due to the high surface energy of the nanosheets. MSs were used as a top layer to effectively increase the light diffuse reflection and harvesting to enhance photogenerated current. In comparison with ZnO NPs photoelectrode, the short circuit current density (Jsc) of ZnO NPs/MSs photoelectrode increased from 10.3 mA/cm2 to 16.0 mA/cm2, which was an enhancement of 55%. To further increase the fill factor and PCE of QDSCs, ZnO NPs/MSs was treated in the solution of H3BO3 and (NH4)2TiF6 to form a barrier surface layer, which suppressed the charge recombination and prolonged electron lifetime. As a result, the solar cell displayed Jsc of 17.13 mA/cm2, Voc of 0.56 V, FF of 0.53, and PCE of 5.08%, one of the highest values for ZnO-based QDSCs at this time.

•Anisotropic NdFeB/SmFeN hybrid magnets were successfully prepared.•The density, magnetic alignment orientation and magnetic properties of the magnets were simultaneously increased.•The maximum energy product of the magnets is above 20 MGOe.The anisotropic hybrid magnets of NdFeB/SmFeN have been prepared through the warm compact process in magnetic field. The thin particles of SmFeN (3–5 µm) enter into the gaps among big particles of NdFeB (80–100 µm), which has remarkable influence on the magnetic properties of hybrid magnets: (a) increasing the density of the magnets; (b) decreasing the content of organic binder in unit volume magnets so as to enhance the effective magnetic properties of the magnets; and (c) improving the magnetic orientation for the high maximum energy product of the magnets. As a result, the anisotropic hybrid magnets with high properties (Br=9.614 KGs, Hcj=13.71 KOe, (BH)max=20.19 MGOe and density=6.23 g/cm3) has been obtained.

Ferromagnetic SmCo nanoparticles with narrow size distribution (5–8 nm) were successfully prepared by polyol co-reduction using non-toxic inorganic precursors (nitrates) instead of deadly poisonous organometallic precursors (acetylacetonate or carbonyl compounds). In the synthesis, Sm3+ and Co2+ can get electrons from acetaldehyde (CH3CHO) and then are reduced to Sm and Co. However, the standard electrode potential of Sm3+ is far lower than that of Co2+ so that Co2+ is reduced early and then grow up quickly. The additive of CH3COOH increases the concentration of H+ and decreases the stability of Sm3+, which results in the co-reduction of the Co2+ and Sm3+. So the SmCo nanoparticles are synthesized in-situ. The coercivity and magnetization of the nanoparticles were 1041 Oe and 55 emu/g, respectively.Highlights► The monodispersed SmCo nanoparticles were successfully prepared by co-reduction. ► The precursors were nitrates instead of organometallics. ► The CH3COOH can control the reaction velocity so as to realize the co-reduction. ► The size of nanoparticles is about 5–8 nm. ► The coercivity of nanoparticle is 1041 Oe.

Radially oriented ring 2:17 type SmCo magnets have different microstructure in the radial direction (easy magnetization) and axial direction (hard magnetization). The structure of the cross-section in radial direction is close-packed atomic plane, which shows cellular microstructure. The microstructure of the cross-section in axial direction consists of a mixture of rhombic microstructure and parallel lamella phases. So the magnets have obvious anisotropy of thermal expansion in different directions. The difference of the thermal expansion coefficients reaches the maximum value at 830–860 °C, which leads to radial cracks during quenching. The magnets have high brittlement because there are fewer slip systems in crystal structure. The fracture is brittle cleavage fracture.

Alloys of Ti–45Al–8.5Nb–0.2B–0.2W–0.1Y and Ti–47.5Al–2.0V–1.0Cr have been prepared by spark plasma sintering (SPS). Their high-temperature oxidation behavior at 1000 °C in air has been investigated. The results indicate that the Ti–45Al–8.5Nb–0.2B–0.2W–0.1Y alloy possesses superior oxidation resistance, which is greatly better than that of Ti–47.5Al–2.0V–1.0Cr alloy under the same condition. The enhanced property is mainly attributable to 8.5 at.% Nb addition. For the Ti–47.5Al–2.5V–1.0Cr alloy, the outer oxide scale is dominated by TiO2 with a small amount of Al2O3, and the inner scale consists of many separate alternating Al2O3/TiO2 layers. By comparison, the inner oxide scale of Ti–45Al–8.5Nb–0.2B–0.2W–0.1Y underneath the outer TiO2-rich layer is composed of TiO2 and a minor amount of TiN. Additionally, Nb is found to be enriched at the interface of the oxide scale and the substrate. The addition of Nb promotes the formation of TiN in the oxide scale and Nb-enriched diffusion layer between the scale and the substrate, which is effective to impede the diffusion of Ti and O ions.

Anisotropic bonded magnets were prepared by warm compaction using anisotropic Nd-Fe-B powder. The forming process, magnetic properties, and temperature stability were studied. The results indicate that the optimal temperature of the process, which was decided by the viscosity of the binders, was 110°C. With increasing pressure, the density of the magnets increased. When the pressure was above 700 MPa, the powder particles were destroyed and the magnetic properties decreased. The magnetic properties of the anisotropic bonded magnets were as follows: remanence Br = 0.98 T, intrinsic coercivity iHc=1361 kA/m, and maximum energy product BHmax = 166 kJ/m3. The magnets had excellent thermal stability because of the high coercivity and good squareness of demagnetization curves. The flux density of the magnets was 35% higher than that of isotropic bonded Nd-Fe-B magnets at 120°C for 1000 h. The flux density of the bonded magnets showed little change with regard to temperature.

Organic–inorganic halide CH3NH3PbI3 (MAPbI3) perovskite solar cells (PSCs) have attracted intensive attention due to their high power conversion efficiency and low fabrication cost. However, MAPbI3 is known to be very sensitive to humidity, and the intrinsic long-term stability of the MAPbI3 film remains a critical challenge. 2-Aminoethanethiol (2-AET) was used as a ligand to bridge the organic compound (MAI) and inorganic compound (PbI2), which restricted the fast growth of PbI2 to realize the synchronous growth environment of MAI and PbI2 crystals, resulting in the formation of a compact MAPbI3 film with polygonal grains. Due to the compact (PbI2)–2-AET–(MAI) molecule barrier layers in the MAPbI3 structure, the resulting perovskite films showed excellent intrinsic water-resistance, with the MAPbI3 perovskite crystal structure retained for a long time (>10 minutes) after immersion in water. This work makes a step towards obtaining long-term stable MAPbI3 perovskite devices.

Quantum dot sensitized solar cells (QDSCs) have attracted considerable attention recently and become promising candidates for realizing a cost-effective solar cell. The design and synthesis of quantum dots (QDs) for achieving high photoelectric performance is an urgent need imposed on scientists. Here, we have succeeded in designing a QDSC with a high efficiency η of 6.33% based on Cd0.8Mn0.2Se quantum dots by facile chemical bath deposition (CBD). The effects of Mn2+ ions on the physical, chemical, and photovoltaic properties of the QDSCs are investigated. The Mn2+ ions doped into QDs can increase the light harvesting to produce more excitons. In addition, the Mn2+ dopant also raises the conduction band of CdSe, accelerates the electron injection kinetics and reduces the charge recombination, improving the charge transfer and collection. The increase of the efficiencies of light-harvesting, charge-transfer and charge-collection results in the improvement of the quantum efficiency of the solar cells. The power conversion efficiency of the solar cell is increased to 6.33% (Voc = 0.58 V, Jsc = 19.15 mA cm−2, and FF = 0.57).

Transition metal chalcogenide nanocrystals have increasingly been used in quantum dot-sensitized solar cells (QDSCs) as a counter electrode (CE) to improve their power conversion efficiency (PCE) due to their high catalytic activity. Herein, we report a Cu3Se2 nanostructured CE composed of nanorods and nanosheets for high efficiency QDSCs. Cu3Se2 nanocrystals were directly grown on the surface of fluorine-doped tin oxide (FTO) glass to form a double-layer morphology via the chemical bath deposition (CBD) process. Nanorod arrays with the height of 100 nm were covered by nanosheets with the size of approximately 500 nm. When the CBD time is 3 h, the QDSC shows the highest efficiency due to the excellent catalytic ability and conductivity of the Cu3Se2 CE. As a result, the PCE of the QDSCs using Cu3Se2 CE has the highest value of 5.05% and average value 4.96%, which are much higher than that of the solar cell using the conventional CE of compact CuxS (4.10% for the highest value and 4.06% for the average value). This is attributed to the large surface area, high conductivity and good electrocatalytic ability of the nanostructured Cu3Se2 CE.