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Sn-based perovskite FASnI3 suffers more severe degradation under light/O2 than only O2 exposure, which is caused by the large amount of superoxide formation at numerous iodine vacancies through the reaction between O2 and photoexcited electrons.

The past decade has witnessed rapid development of perovskite solar cells (PSCs), the record power conversion efficiency (PCE) of which has been rapidly boosted from the initial 3.8% to a certified 25.5%, approaching the Shockley–Queisser (SQ) limit for single-junction solar cells. Tandem solar cells (TSCs) have gradually attracted more attention due to their great potential to break the SQ limit by reducing the thermalization losses. Among various kinds of perovskite-based tandems, all-perovskite TSCs offer great promise with the advantages of solution processability, low cost, and flexibility. As top cells for TSCs, the wide-bandgap (wide-Eg, >1.7 eV) PSCs play an essential role in harvesting the high-energy photons and providing high open-circuit voltage (Voc) for the multi-junction TSCs, which is helpful for maintaining the stability of the bottom cell by filtering harmful ultraviolet radiation. However, both organic–inorganic hybrid perovskites and all-inorganic perovskites encounter several problems, such as the phase instability and the large Voc deficits (Eg/q − Voc), which result in inferior performance of wide-Eg PSCs. Many efforts have been made to overcome the issues and researchers have already made encouraging progress. In this review, we summarize the recent progress on wide-Eg PSCs based on organic–inorganic hybrid perovskites and all-inorganic perovskites, as well as their application in all-perovskite TSCs. Finally, the main challenges and perspectives are discussed.

Wide-bandgap (wide-E g , ∼1.7 eV or higher) perovskite solar cells (PSCs) have attracted extensive attention due to the great potential of fabricating high-performance perovskite-based tandem solar cells via combining with low-bandgap absorbers, which is considered promising to exceed the Shockley–Queisser efficiency limit. However, inverted wide-E g PSCs with a minimized open-circuit voltage (V oc) loss, which are more suitable to prepare all-perovskite tandem devices, are still lacking study. Here, we report a strategy of adding 1,3,5-tris (bromomethyl) benzene (TBB) into wide-E g perovskite absorber to passivate the perovskite film, leading to an enhanced average V oc. Incorporation of TBB prolongs carrier lifetimes in wide-E g perovskite due to reduction of defects in perovskites and makes a better energy level matching between perovskite absorber and electron transport layer. As a result, we achieve the power conversion efficiency of 17.12% for our inverted TBB-doped PSC with an enhanced V oc of 1.19 V, compared with that (16.14%) for the control one (1.14 V).

Urolithiasis has become more prevalent throughout China.Knowing stone composition helps identify their possible underlying etiology of urolithiasis, provide appropriate individualized treatment and prevent stone recurrence.To explore characteristics of urinary stone composition in China, and determine the effects of gender, age, body mass index (BMI), stone localization and geographical region on stone composition.We used Fourier transform infrared spectroscopy to analyse urinary stones from consecutive patients at 46 hospitals in seven geographic areas of China between June 1, 2010 and May 31, 2015.Chi-squared tests and logistic regression analyses were performed to determine associations between stone composition and sex, age, body mass index (BMI), stone location, and geographic region.The most common stone components were calcium oxalate (CaOx; 65.9%), carbapatite (15.6%), urate (12.4%), struvite (2.7%), brushite (1.7%), and cystine (0.9%). CaOx and urate occurred more frequently in males, whereas carbapatite and struvite were more common in females (p

Flexible perovskite solar cells (PVSCs) show promising applications in terrestrial power plant systems irrespective of curved surfaces, but still suffer from low efficiencies and poor stabilities. Here, we report a synergetic strategy of combining bromine (Br) and cetyltrimethylammonium chloride (CTAC) additives to passivate both bulk and surface defects, leading to improved performance and stability of flexible PVSCs. Incorporation of Br suppresses the formation of halide vacancies in the perovskite bulk, while CTAC further modifies the film surface with reduced defects and enhanced hydrophobicity features. As a result, flexible PVSCs with efficiencies over 18% are achieved with high reproducibility, compared to the control devices with efficiencies about 17%. Our flexible PVSCs present excellent ambient stability against moisture, keeping over 90% of the initial efficiency after exposure to 90% humidity for about 170 hours. Our work offers a facile and universal strategy for the fabrication of high performance and stable flexible PVSCs.

In this paper, MgxZn1-xO (MZO) films with x from 0 to 0.25 were prepared by radio frequency (RF) magnetron co-sputtering, and the structure, surface morphology, optical and electronic properties of MZO films were investigated. With the increase of Mg content, the crystallinity of MZO films became worse with the appearance of grain agglomeration, and the optical energy band gap (Eg) linearly changed from 3.228 eV to 3.824 eV. The MZO films with different Mg content were used as the window layer for CdTe solar cells with or without CdS layer. The efficiency of MZO/CdTe devices is much lower than MZO/CdS/CdTe devices. Incorporating a buffer layer CdS into CdTe solar cells can significantly improve the devices efficiency, and the devices still maintain a high spectral response in the short wavelength region.

Achieving high open-circuit voltage ( V o c ) for CdTe thin film solar cells is challenging. We report that a ZnMgO (ZMO) buffer can improve V o c and the performance of CdTe solar cells when deposited on the tin oxide (SnO2 or TO) coated fluorine-doped tin oxide (FTO) substrates. The TO/ZMO bilayer buffer brings a better energy band matching at the front contact of CdTe thin film solar cells, which can reduce interface carrier recombination and facilitate electron extraction. Our best-performing CdTe solar cell using the TO/ZMO bilayer buffer has achieved a power conversion efficiency of 16.76%, with an open-circuit voltage of 838.75 mV, a short-circuit current density of 27.32 mA cm−2, and a fill factor of 73.14%, much higher than those of devices based on TO buffer. Our results suggest that a careful interface modification of front contact layers provides a simple and effective route to further improving the performance of CdTe solar cells with a higher V o c .

Observational studies on the association between tofu intake and breast cancer incidence have reported inconsistent results. We reviewed the current evidence and quantitatively assessed this association by conducting a dose-response meta-analysis. The electronic databases PubMed and EMBASE were searched for relevant studies published up to August, 2018. We included epidemiological studies that reported relative risks (RRs) or odds ratios (ORs) with 95% confidence intervals (CIs) for the association between tofu intake and breast cancer risk. A total of 14 studies (2 cohort studies, 12 case-control studies) were included in the meta-analysis. The overall OR of breast cancer for highest vs lowest intake of tofu was 0.78 (95% CI 0.69-0.88), with moderate heterogeneity (P = 0.011, I2 = 49.7%). Dose-response analysis based on 5 case-control studies revealed that each 10 g/d increase in tofu intake was associated with 10% reduction in the risk of breast cancer (95% CI 7%-13%, P = 0.037, I2 = 40.8%). In summary, our findings suggest an inverse dose-response association between tofu intake and risk of breast cancer. However, owing to the limitations of case-control studies, more properly designed prospective studies are warranted to confirm this association.

It is critical to understand the dominant recombination mechanisms of thin film solar cells for further improving their performance. The dominant recombination paths of CdTe solar cells with MgxZn1-xO (MZO), MZO/CdS and MZO/CdS/CdSe buffer layers were investigated by temperature-dependent current-voltage (JVT) characterization both in light and dark, with traditional CdS/CdTe devices as a reference. The devices with MZO or MZO/CdS buffer layers are confirmed to be dominated by interface recombination, which leads to poor performance of devices. Compared to devices with traditional CdS buffer layers which are dominated by bulk recombination, the devices with MZO/CdS/CdSe buffer layer exhibit the same dominant recombination path but superior performance. It demonstrates that MZO/CdS/CdSe can be a promising composite buffer layer.

Poor qualities of ZnMgO thin films are likely to be obtained at higher Mg content, which can decrease the performance of ZnMgO-based devices. This study focuses on improving the qualities of ZnMgO thin films to increase the performance of CdTe solar cell. It is found that the rapid thermal annealing (RTA) treatment increases the crystallinity, eliminates defects and improves the conductivity of ZnMgO thin films. These are helpful to suppress the recombination caused by bulk and interface defects as well as to reduce the cell's series resistance. The Fermi level moves close to conduction band and both the conduction and valence band energy shift lower relative to band energy of CdSSeTe film after RTA, which could not only increase the built-in voltage but also enhance the electron transport and block the hole recombination. As a result, the efficiency of CdTe solar cells is enhanced when using the RTA-treated ZnMgO, with maxium power conversion efficiency reaching values of 15.7%, which are much higher than those of the cells with the as-grown ZnMgO (11.6%). RTA is proved to be one of the excellent methods to control the properties of ZnMgO for improving the performance of CdTe solar cell.

The short-wavelength response for traditional CdS/CdTe thin film solar cells was dramatically restricted by the CdS window layer. In order to increase short-wavelength light collection, we tried to replace CdS with MgxZn1−xO (MZO). The short-wavelength quantum efficiency (QE) response was obviously increased to more than 80% at 400 nm, while fill factor (FF) and open circuit voltage (Voc) for CdTe solar cells were decreased. This decrease was mainly caused by the weak build-in potential formed by the MZO/CdTe heterojunction, which resulted in insufficient driving force to repel the photo-generated carriers. Hence, the thin CdS buffer layer was introduced between MZO and CdTe to improve the built-in potential. It efficiently increased the build-in potential from 0.369 to 0.579 V with an obvious improvement of FF and Voc. But this interlayer caused QE losses to some degree in the short-wavelength region. To avoid these losses, a composite CdS/CdSe buffer layer was incorporated in the CdTe solar cells. CdSe acted as a protective layer to avoid the excessive CdS consumption during the high temperature deposition processing of the CdTe absorption layer. Meanwhile the formation of CdSexTe1−x by inter-diffusion extended the long-wavelength response. Thus, cell performance was enhanced with a relatively high build-in potential 0.517 V and a substantial improvement of the QE response.

Cd2SnO4 (CTO) thin films were prepared by RF sputtering technique from a CTO target and then annealed under Ar or Ar/CdS atmosphere. The detailed characterizations on the surface properties of as-deposited, Ar-annealed, and Ar/CdS-annealed CTO thin films were carried out by AFM, XPS, UPS, etc. The surface properties of the films are greatly dependent on the annealing atmosphere. Ar/CdS atmosphere promotes the grains to grow but slightly increases the surface roughness. Cadmium atoms sublimated off the CTO thin films during the annealing process and this sublimation can be suppressed under Ar/CdS atmosphere, which causes the surface of CTO thin films not homogeneous as inside. The fundamental band gap is determined to be 2.83 eV. The Fermi level position is 1.7 eV above the valence band maximum for the as-deposited films, while it shifts to 2.98 eV and 3.21 eV for the films annealed in Ar and Ar/CdS atmospheres, respectively. Work function for the Ar/CdS-annealed films is about 0.16 eV higher than the Ar-annealed ones. These results could be used to design high efficiency thin film solar cells and water photolysis devices, in which the efficiency is sensitive to the surface properties of TCO thin films.

Organic–inorganic hybrid perovskite solar cells have attracted significant research attention in terms of perovskite materials, fabrication, device architecture, and interfacial engineering to increase their power conversion efficiency (PCE). However, the state-of-the-art front electrode of perovskite solar cells is mainly focused on indium tin oxide (ITO) and fluorine-doped tin oxide (FTO). To further improve the optical characteristics of front electrodes for perovskite devices, it is necessary to explore a new and suitable transparent conductive oxide material. Herein, we introduce a Cd2SnO4 film for constructing a perovskite device with a novel structure. The as-prepared Cd2SnO4 film shows higher optical transmission in the visible region compared to the FTO substrate. The matching energy band alignment can ensure efficient carrier transport and collection between the TiO2 layer and Cd2SnO4 electrode. The higher PCEs with an average of 15.58% under AM 1.5 irradiation for Cd2SnO4-based perovskite solar cells were obtained compared to those of the FTO-based devices. This renders the Cd2SnO4 film a promising transparent conductive oxide candidate for highly efficient perovskite solar cells. However, the toxicity of lead and cadmium components still remain a major concern for its commercial applications.

Using a gradient band gap absorption layer to ensure high short-circuit current density is one of the key factors to prepare high-efficiency CdTe solar cells. CdSexTe1-x films with different selenium compositions were prepared by vacuum co-evaporation deposition technology. The effects of composition changes on the structure, morphology and properties of the films were studied. CdSexTe1-x films were incorporated into the CdTe solar cells with the structure of Glass/SnO2:F/CdS/CdSexTe1-x/CdTe/ZnTe:Cu/Au. The results show that the structure of CdSexTe1-x films is cubic when x is 0, 0.23 or 0.41, and while x is 0.61, 0.78 or 1 the structure is hexagonal. The minimum optical band gap is 1.40 eV with x = 0.41. It is found that in the long wavelength region, the cut-off edge of quantum efficiency curve depends on not only the thickness of CdSexTe1-x film with specific Se composition, but also the whole preparation process of solar cells. After using a 70 nm CdSe0.41Te0.59 film and 70 nm ZnTe:Cu back contact buffer layer, the cut-off edge of the long wavelength region can be reduced to 1.40 eV and the short-circuit current density of the device without antireflection layer reaches up to 28.8 mA/cm2.

We report use of lithium chloride (LiCl) as a non-Cd dopant to deal with the environmental issues associated with use of traditional CdCl2 dopant in CdTe solar cells. It has been found that, after LiCl treatment, device performance parameters including external quantum efficiency and conversion efficiency were improved considerably, being comparable to those of a counterpart treated with CdCl2. The optimal efficiency of 9.58% was obtained at 405°C, and V oc as high as ∼737.3 mV was obtained at 385°C. Thorough study of the properties of the CdTe film treated by LiCl by x-ray diffraction analysis, scanning electron microscopy, x-ray photoelectron spectroscopy, and secondary-ion mass spectroscopy further verified the feasibility of posttreatment with nontoxic LiCl for fabrication of CdTe photovoltaic devices. The doping level of p-type CdTe thin film was improved by lithium. This represents a nontoxic approach for fabrication of commercial CdS/CdTe thin-film solar cells with better performance.

As an important functional film, tin dioxide (SnO2) was widely used in the communities of gas sensors as well as solar cells. SnO2 (110) and (100) surfaces were thought to be stable, and both could be easily obtained by common preparation method. The characteristics of SnO2 surface were critical to the performance of devices when it was applied in solar cells, and the SnO2 (100) surface had not been understood explicitly. A series of SnO2 (100) surface models with different terminal atoms were built in this work and calculated by density functional theory (DFT) with GGA + U. SnO2 (100) surfaces with different terminal atoms exhibited distinctly different surface states. Basically, these surface states mainly originated from the terminal atoms, and they extended to the tenth monoatomic layer. SnO2 (100) surface terminated with single monolayer of O atoms was the structure with the least surface states. The real surface of SnO2 was thought to be consisting of O terminal atoms mostly. The charge neutral level of SnO2 (100) surface was thought to be 2.94 eV above the valence band.

The methylammonium lead halide perovskite solar cells have become very attractive because they can be prepared with low-cost solution-processable technology and their power conversion efficiency have been increasing from 3.9% to 20% in recent years. However, the high performance of perovskite photovoltaic devices are dependent on the complicated process to prepare compact perovskite films with large grain size. Herein, a new method is developed to achieve excellent CH3NH3PbI3-xClx film with fine morphology and crystallization based on one step deposition and two-step annealing process. This method include the spin coating deposition of the perovskite films with the precursor solution of PbI2, PbCl2, and CH3NH3I at the molar ratio 1:1:4 in dimethylformamide (DMF) and the post two-step annealing (TSA). The first annealing is achieved by solvent-induced process in DMF to promote migration and interdiffusion of the solvent-assisted precursor ions and molecules and realize large size grain growth. The second annealing is conducted by thermal-induced process to further improve morphology and crystallization of films. The compact perovskite films are successfully prepared with grain size up to 1.1 μm according to SEM observation. The PL decay lifetime, and the optic energy gap for the film with two-step annealing are 460 ns and 1.575 eV, respectively, while they are 307 and 327 ns and 1.577 and 1.582 eV for the films annealed in one-step thermal and one-step solvent process. On the basis of the TSA process, the photovoltaic devices exhibit the best efficiency of 14% under AM 1.5G irradiation (100 mW·cm(-2)).

The application of thinner cadmium sulfide (CdS) window layer is a feasible approach to improve the performance of cadmium telluride (CdTe) thin film solar cells. However, the reduction of compactness and continuity of thinner CdS always deteriorates the device performance. In this work, transparent Al2O3 films with different thicknesses, deposited by using atomic layer deposition (ALD), were utilized as buffer layers between the front electrode transparent conductive oxide (TCO) and CdS layers to solve this problem, and then, thin-film solar cells with a structure of TCO/Al2O3/CdS/CdTe/BC/Ni were fabricated. The characteristics of the ALD-Al2O3 films were studied by UV&ndash, visible transmittance spectrum, Raman spectroscopy, and atomic force microscopy (AFM). The light and dark J&ndash, V performances of solar cells were also measured by specific instrumentations. The transmittance measurement conducted on the TCO/Al2O3 films verified that the transmittance of TCO/Al2O3 were comparable to that of single TCO layer, meaning that no extra absorption loss occurred when Al2O3 buffer layers were introduced into cells. Furthermore, due to the advantages of the ALD method, the ALD-Al2O3 buffer layers formed an extremely continuous and uniform coverage on the substrates to effectively fill and block the tiny leakage channels in CdS/CdTe polycrystalline films and improve the characteristics of the interface between TCO and CdS. However, as the thickness of alumina increased, the negative effects of cells were gradually exposed, especially the increase of the series resistance (Rs) and the more serious &ldquo, roll-over&rdquo, phenomenon. Finally, the cell conversion efficiency (&eta, ) of more than 13.0% accompanied by optimized uniformity performances was successfully achieved corresponding to the 10 nm thick ALD-Al2O3 thin film.