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Dissimilar joining of CFRP and conventional metal attracts tremendous interest due to the increased usage of CFRP in the aerospace industry. However, until now, laser joining of CFRP to metal is commonly performed with low welding velocity (

Ultraviolet (UV) photodetectors with high responsivity, fast response speed and better stability have attracted much attention. In this work, heterojunctions based on ZnO nanorods (ZnO NRs)/CuI were successfully prepared by combinational chemical hydrothermal and drop-coating methods, which could be employed as self-powered and external powered UV photodetectors. The ZnO NRs were homogeneous covered and coated by CuI layer. The introduction of CuI enhanced the UV emission and weakened the defect emission of ZnO. The space-limited domain annealing was adopted to post-treat the CuI layer, which is useful to prevent the significant loss of iodine in the thin films. The UV photodetector based on ZnO NRs/CuI shows the responsivities of 86.84 mA W−1 at 0 V bias voltage and 4.41 × 104 mA W−1 at −2.5 V bias voltage under 380 nm irradiation. The rise and decay time for the devices are both 110 ms. The incorporation of CuI benefits the separation of photon-generated carriers. The facile, practical and low-cost synthesis makes ZnO NRs/CuI heterojunction a potential candidate for vertical UV-A photodetectors with high responsivity.

Highly efficient CdTe solar cells were fabricated by introducing rGO@CuSCN as a composite back contact. The rGO@CuSCN was prepared by convenient solution-processed method. As a Cu-doping source and electron reflection layer, CuSCN could facilitate to dope CdTe and decrease the carrier recombination on the back surface of CdTe. The rGO, as a hole transport layer, could suppress unfavorable over-diffusion of Cu and improve hole collection and transport. The results show the obvious reduction of back barrier height and decrease of the dark current density in the devices with rGO@CuSCN back contact. Using facile coating method and optimal thermal annealing for the preparation of rGO@CuSCN composite back contact, CdTe solar cell presented greatly enhanced photovoltaic performance (Eff: 16.84%, Voc: 841 mV, Jsc: 26.83 mA/cm2, FF: 74.6%).

Copper doping in polycrystalline CdTe thin films and optimal band alignment at the CdTe/back-contact interface are critical for obtaining high performance devices. A CuCl2 solution treatment was used in this work to enhance the p-doping of CdTe. The carrier density of CdTe was increased from 4.72 × 1013 to 1.11 × 1014 cm−3 and the open circuit voltage of the device was obviously improved more than ~50 mV from 728 to 783 mV. In order to further improve device performance, Te/Cu bilayer using rapid thermal processing was implemented to reduce barrier at the back contact. The short time-high temperature process efficiently activated the Te/Cu bilayer back contact and precisely controlled the Cu diffusion. The proper dose of Cu diffusion can further increase the p-doping of CdTe (~2.22 × 1014 cm−3), resulting in the apparent increase in response from the CdS spectral region. The chemical reaction occurred between Te and Cu after rapid thermal processing treatments causing the formation of the CuxTe phases, which can form a barrier in the conduction band to reflect electrons and reduce recombination at the back contact. With the increase of the temperature, the open circuit voltage of the device increased. However, the device with excessive Cu contacted at higher temperature showed the reduction in response in the long-wavelength region and decrease in fill factor due to the formation of much more Cu-related recombination states. Finally, open circuit voltage of > 820 mV, and fill factor of > 72% for CdTe solar cells with an area of 0.24 cm2 were achieved.

The Schottky barrier between the CdTe layer and metal electrode has opposite polarity to the CdS/CdTe cell junction, which can greatly degrade cell performance. Adding a back contact (BC) layer can reduce the Schottky barrier at metal/p-CdTe interfaces. Paste including CuTe nanoparticles and carbon nanotubes (CuTe NPs/CNTs) was used as a BC in thin-film CdTe solar cells. The effect of the mass of carbon nanotubes (CNTs) in the paste and the BC annealing temperature on cell performance was explored. Cu film and paste including Cu nanoparticles and carbon nanotubes (Cu NPs/CNTs) were fabricated as the BC for CdTe solar cells. The performance of CdTe solar cells based on different kinds of Cu-containing BCs studied. The fill factor and open-circuit voltage (V OC) of devices with CuTe NPs/CNTs BC were greatly improved by optimizing the mass of CNTs in the paste and the annealing temperature. The carrier concentration in the CdTe layer was improved by one order of magnitude. The CuTe NPs/CNTs BC showed the best effect on cell efficiency for the Cu-containing BC.

Phase control is important to obtain high-performance CdTe solar cells when copper telluride is used as a back-contact for CdTe solar cells. In this paper single-phase CuTe was mainly controlled by the Cu/Te ratio via a co-evaporation method in combination with rapid thermal processing treatments. The alloy thin films as-deposited were mainly amorphous. After thermal treatments, the films experienced the phase transformation from mixed phases of CuTe and Cu1.4Te to single phase CuTe and then to coexisting phases. Single phase CuTe thin films were p-type semiconductor compounds and had a high carrier concentration, ∼1021 cm−3. With the copper telluride buffer layer, device performance than those without the buffer layer has been obtained. Moreover, single-phase orthorhombic CuTe contact buffer layer obviously improved diode characteristics and enhanced the device performance.

The study of CdS/CdTe solar cells has become popular in the photovoltaic field, in which the highest efficiency achieved is more than 20%. However, the CdTe thin film as the absorbing layer doesn’t perform very well in the long wavelength photon absorption regime. Here, a new single offset superlattice was designed to be the composite absorbing layer, which is based on a super lattice-structure of CdTe/ZnTe using cycle growth. Different cycles are to applied to the solar cells to characterize properties with respect to the super lattice. The crystallinity and transmission spectrum as well as the cross sectional morphology of the ZnTe/CdTe composite layers with different cycles are also characterized in this work. X-ray diffraction analysis showed that there is a strong (111) preferred orientation of CdTe growth. The solar cells based on the structure of FTO/CdS/CdTe/ZnTe:Cu/(ZnTe|CdTe) n /ZnTe:Cu/Au are fabricated which exhibited a desired spectral response in the range of 550–800 nm and still possess slight spectral response in the range of 850–900 nm. The photoelectric conversion efficiency of the cell of this structure is 12.8%, with a short-circuit current density of 25.59 mA/cm 2 and fill factor of 66.8%, significantly improving these properties compared with a cell without the composite layer. This structure can improve the spectral response of the solar cell when integrated with other leading technologies.

In recent years, the power conversion efficiency (PCE) up to 20% was obtained based on CdTe solar cells consisting of Glass/SnO2: F/SnO2/CdS/CdTe/ZnTe: Cu/Au. The underlying carrier transport and collection mechanisms of this architecture become complicated while quantum efficiency with external direct current bias is tremendously informative. Quantum efficiency measurement under forward voltage changes dramatically and it is defined as apparent quantum efficiency (AQE). It is accessible to give insight to the impact of the high resistant transparent buffer layer and CdS window layer on the carrier collection mechanism and photocurrent loss. Herein, five simpler structures were fabricated and tested together with the structure mentioned above for both direct current (DC) and alternating current (AC) modes of quantum efficiency under forward bias and four types (470 nm, 525 nm, 780 nm, 850 nm) of monochromatic light to achieve a pair of I-V curves under different light intensities. Comparing the AQE acquired via applying various forward bias with different device structures along with their collection efficiency of different wavelength, it is available to establish the connection between AQE effects and device structures. The consistent tendency of the AQE response under DC mode at forward bias for different structures of CdTe devices indicates a same current direction without phase shift. While the introduction of SnO2 buffer layer is prone to generate a large phase angle in the shortwave AQE response, resulting in AQE > 1. When there is no photoconductive CdS layer, the device photocurrent under forward bias changes slightly and uniformly in the measured spectra, avoiding intricate band diagram in the CdS region.

In this work, a post annealing process in CdCl2 was applied to improve the quality of pulsed laser deposited CdS films, and the effect of annealing temperature on the quality of CdS films was studied. The research indicated that the grain size of CdS thin films obviously increased after the annealing process, and crystallinity and optical transmission performance of CdS films were enhanced as well. Moreover, the CdTe solar cell with the annealed CdS window layer obtained better performance. The annealing temperature is a significant factor in the annealing process. 420 °C may be an optimistic annealing temperature, since not only the CdS layer annealed at this temperature had good crystallinity and optical transmission performance with a relatively smooth surface, but also the photovoltaic device with this window layer obtained the best performance among all the samples, including higher short-circuit current, open-circuit voltage and efficiency, corresponding to 26.97 mA/cm2, 760.80 mV and 12.37% respectively.

Polycrystalline CdTe thin films for CdTe solar cell devices are grown using vapor transport deposition (VTD) which is one of promising techniques to prepare CdTe thin film for high efficiency CdTe solar cells. However, few works report the study of the CdTe thin film growth by VTD so far. In this paper, the oxygen concentration is altered to be O2-free, 10, 20, 30, 40 and 50%. The morphology and crystallinity of as-deposited CdTe films are studied by X-ray diffraction and scanning electron microscopy. And the electrical properties for CdTe photovoltaic devices is investigated by current–voltage (J–V), capacitance voltage (C–V), and time-resolved photoluminescence spectroscopy (TRPL) measurements. The results show that a small amount of oxygen in the process has a positive impact on CdTe thin film quality because the oxygen incorporation could effectively change the grain size and make grain orientation more pronounced. The carrier concentration increases from 2.3 × 1013 to 7.5 × 1013 cm−3 when the oxygen concentration increases from 0 to 10%. The result of carrier lifetime also shows a positive correlation with oxygen concentration. A series of devices performance reveal the optimal technological conditions is under 10% oxygen partial pressure. The best small-area CdTe thin film solar cell is obtained with the conversion efficiency of 12.65% without back contact layer.

Grain boundaries and interfacial impurities are the main factors that limit the further development of polycrystalline perovskite solar cells because their existence severely deteriorates the device performance. In order to optimize the efficiency of perovskite solar cells, it is essential to eliminate these defects. In the present work, potassium iodide (KI) is incorporated into the perovskite absorber. KI incorporation improves the crystallinity of the perovskite, increases the grain size, and decreases the contact potential distribution at the grain boundary, which are verified by X-ray diffraction, scanning electronic microscopy and Kelvin probe force microscopy. Besides, the activation energy of the recombination, estimated from the temperature dependent current–voltage of perovskite solar cells, is larger than the bandgap calculated from the temperature coefficient. These suggest that KI incorporation effectively passivates the grain boundaries and interfacial defects. As a result, charge trapping in the absorber as well as the bimolecular and trap-assisted recombination of the device are significantly suppressed. Consequently, the open circuit voltage and fill factor of the incorporated devices are greatly improved, enabling an optimized power conversion efficiency of 19.5%, in comparison with that of 17.3% for the control one. Our work provides an effective strategy of defect passivation in perovskite solar cells by KI incorporation and clarifies the mechanism of the performance optimization of KI incorporated devices.

In this paper, we demonstrate a new heterojunction ultraviolet (UV) photodetector in a superstrate configuration, i.e. glass/FTO/ZnO NRs/rGO/Au, constructed via the dip-coated method to form reduced graphene oxide (rGO) layer on the surface of ZnO nanorod arrays (NRs). The rGO compensates for surface oxygen vacancies by the oxygen-containing groups and improves the crystal properties of ZnO NRs after annealing. Furthermore, the carrier mobility and work function are effectively increased after Au doping. Under UV irradiation, the electron–hole pairs generated by ZnO NRs are separated with bias voltage, and the electrons and holes are collected via fluorine-doped tin dioxide (FTO) and rGO/Au, respectively. The rGO acts as a hole transport layer, which reduces the recombination of carriers and increases the current density, giving rise to a higher responsivity (67.48 A W−1 at −1.5 V bias) than pure ZnO NRs photodetectors.

Transient absorption (TA) spectroscopy is considered as a powerful technique that reflects the ultrafast dynamics of photogenerated carriers in photoelectric and photocatalysis materials. However, limited by its sensitivity, the photogenerated carrier density in TA measurements of solar energy materials is usually much higher than that in the real working condition. Here, we present a combination of kHz macro-pulse and MHz micro-pulse technique for an ultrahigh sensitive TA spectrometer, which improves the sensitivity to the 10-7 level of ΔOD. It enables us to study ultrafast carrier dynamics pumped by very low power, which can avoid the influence of many-body interactions and the nonlinear effect associated with high carrier density. This work provides a novel TA method with ultrahigh sensitivity, which will play an important role in investigating the carrier dynamics of semiconductors in the working condition.

To introduce a novel technique of using individualized 3D printing occipitocervical fusion instrument (3D-OCF) for the treatment of upper cervical deformity with atlantoaxial joint dislocation.The surgery for deformity of the craniocervical junction area is a challenge in the field of spine. If the surgical deviation is too large to injure the spinal cord or vertebral artery, it will cause catastrophic damage to the patient. Therefore, it is controversial whether these patients should undergo surgical treatment. We provide a novel surgical approach for the challenging upper cervical surgery through 3D-OCF and a typical patient.We present a 54-year-old female patient, who suffered from dizziness and numbness in her limbs for 8 months. After the patient was admitted, we performed the three-dimensional CT scan, modeled using Mimics software 17.0, and designed customized occipitocervical fusion instrument. Besides, we repeatedly perform simulated surgery based on 3D-printed models before surgery.The operative time was 142 minutes and the intraoperative blood loss was 700 mL. X-ray showed reduction of atlantoaxial dislocation and accurate position of internal fixation. The patient's symptoms were significantly relieved: the sensation of dizziness and numbness of limbs was obviously relieved, and the sense of banding in chest, abdomen, and ankle was disappeared. At the last follow-up, imaging showed that 3D-OCF had bone-integration and Syringomyelia was disappeared. The patient's cervical JOA (Japanese Orthopaedic Association) score increased from 10 points to 17 points.Individualized 3D-OCF can improve the safety and accuracy of upper cervical surgery, reduce the operative time and the number of fluoroscopy. Our study provides a novel surgical approach for the challenging upper cervical surgery.

Although laser welded Al–Li alloys show great potential for application in aerospace industry, the detailed relationship between local hardness and complex microstructure remained unclear. In the present study, relationship between precipitation behavior and local hardness in a defect-free laser pressure weld of Al–Li alloy 2198 was systematically examined by transmission electron microscopy. Hardness profile of the laser pressure weld was reduced in the vicinity of the weld center, mainly explained by size and density of the strengthening precipitates. Moreover, post-weld aging increased the density of strengthening precipitates in the precipitate-dissolved regions, increasing their hardness values markedly. On the other hand, a few precipitates were formed in the precipitate-coarsened regions during post-weld aging, which slightly increased the local hardness. The variation in hardness during post-weld aging could be well correlated with the precipitation behavior in each region of the laser pressure weld.

AlSb films which are a promising absorber layer for thin film solar cells were grown on glass substrate at different substrate temperature ranging from room temperature to 400 °C on glass substrates using aluminum-antimony alloying target by pulsed laser deposition (PLD) technique. Structural, optical and electrical properties of AlSb thin films were studied by X-ray diffraction (XRD), ultraviolet–visible spectrophotometer and a home-made four-probe-contact high temperature system respectively. XRD pattern shows that AlSb film is amorphous at room temperature, but when substrate temperature is higher than 100 °C, AlSb films present cubic phase structure with the preferential orientation of (111) plane. And intensity of diffraction peaks of AlSb film prepared at substrate temperature of 200 °C are stronger than that of other substrate temperature. The electrical measurement results show that conductivity activation energy of AlSb film is 0.25 eV and 0.28 eV. The indirect optical band gap is about 1.63 eV, which is very close to its theoretical value of 1.62 eV. The results of energy dispersive spectrometer (EDS) indicated the ratio of Al to Sb of AlSb films is about 1:1.

Aluminum antimony (AlSb) is a potential absorber for solar cells. In present work, we fabricated AlSb thin films by using pulsed laser deposition method, and investigated the influence of substrate temperature on the structural, electrical and optical properties of AlSb thin films. The results suggested that the AlSb thin films were crystal when the substrate temperature was higher than 300 °C. The average grain size of AlSb films increased and the electrical resistivity decreased with the increase of substrate temperature. At the optimized temperature of 400 °C, the optical band gap of AlSb thin film was 1.82eV. The simulated device performance of ZnS/AlSb ultra-thin solar cells showed that the power conversion efficiency was 18.01% and the quantum efficiency values were higher than 55% in the visible range.

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.

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.

Because of good high temperature conductivity (Mn,Co)3O4 is a promising oxide coating for solid oxide fuel cell interconnect. High-temperature oxidation of Co-Mn alloys at 750 °C and 850 °C at 105 Pa oxygen reveals that formation of a continuous (Co,Mn)3O4 spinel layer significantly decreases oxidation rate constant but not the same for the discontinuous spinel layer. Co-40Mn fine grain alloy coatings are prepared by high-energy micro-arc alloying process (HEMAA). Microstructures and compositions after preparation and oxidation were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). When pre-oxidized under an oxygen pressure of 105 Pa at 850 °C for 10 h, Co-40Mn coatings are transformed into the external oxide which is mainly composed of (Co,Mn)3O4 and Mn3O4. The results disclose Cr outward transport from the stainless steel is significantly suppressed by the as-prepared (Co,Mn)3O4 oxide coatings, when coatings oxidized at 800 °C for 100 h in wet air. The composited spinel coatings have excellent high temperature oxidation resistance and electrical performance.

CdS/CdSe bi-layer film was prepared by pulsed laser deposition with different substrate temperatures as an improved window layer for CdTe solar cells. The total thickness of each CdS/CdSe bi-layer film was about 70 nm, which could contribute to comparatively high transmittance of photons and, therefore, improving the photocurrent. Substrate temperature influenced the properties of the CdS/CdSe bi-layer films and the study showed that the bi-layer film prepared at 400 °C achieved the best optical transmittance and crystallinity. The crystal structure and optical transmittance of CdS/CdSe/CdTe stack before and after CdCl 2 annealing treatment were investigated by utilizing X-ray diffraction and UV/Vis spectrophotometer, respectively. It showed that further CdCl 2 annealing treatment improved the inter-diffusion of Se into CdTe, facilitating the formation of a CdTe 1−x Se x alloy in the absorber layer. Comparing with CdTe, the alloy actually showed a smaller band gap which produced an obvious red shift of the absorption edge in long wavelength region. CdSe window layer was consumed by the inter-diffusion, while enhanced the short wavelength response in the range of 300–500 nm. The device based on CdS/CdSe window layer realized a J SC enhancement due to the improved collection within both short and long wavelength regions accompany with a V OC enhancement when compared to CdS/CdTe solar cell. The CdTe cell with CdS/CdSe bi-layer window deposited at 200 °C showed an efficiency of 13.47% with V OC of 791 mV and J SC of 27.40 mA/cm 2 .

Over the past few years, the studies of CdS/CdTe solar cells have become the mainstream, which have achieved good performance of exceeding 20 %. Here, we prepare CdSe thin films by pulsed laser deposition (PLD) which is one of promising techniques to synthesize semiconductor thin films. In this paper, the optical and electrical properties as well as the crystal structure of CdSe thin films deposited under different temperatures are investigated. We find that the deposition rate adds firstly, and then decreases with the increase of substrate temperature. Transmittance spectrum suggests the absorption edges of CdSe thin films under the condition of high temperature move towards short wavelength. The band gaps of CdSe thin films are 1.948, 1.976, 2.013 and 1.978 eV at the deposition temperature of 150, 250, 350, 450 °C, respectively. X-ray diffraction analysis indicates the formation of cubic phase with a strong (111) preferential orientation. The surface morphology of CdSe thin film and the cross-sectional structure of CdSe/CdTe layer are also analyzed. Based on these studies, we further fabricate the CdSe (PLD)/CdTe solar cells that present excellent performance of response in the range of long wavelength over 900 nm and a good efficiency of near 10 % has been realized.

Industrial application of copper often requires a joining. Unfortunately, a commercial laser welding of this material is challenging due to extremely high reflectivity of copper at the near-infrared wavelength. In this work, the sound copper joints were produced at relatively high welding speed of 15 m/min by using a pressure-assisted fiber-laser welding. It was theoretically shown that the material melting arisen from a convergence of multiple reflections of the laser beam. By using electron backscatter diffraction (EBSD), it was found that microstructural changes were induced by a laser-induced thermal effect as well as a roller-induced pressure. It was deduced that the molten material solidified before feeding to the pressure rolls and thus it experienced a notable plastic strain during the welding process. The present work provides an effective method for commercial joining of high-reflective metals by using the near-infrared fiber laser.

Multilayered MoO3/Cu thin films were prepared by thermal evaporation in combination with the thermal treatments. As-deposited multilayers are amorphous structure. With the increase of temperature, Mo4O11 phase forms in the thin films without copper while MoO2 phase with the weak reduced molybdenum oxide appears in the copper-containing thin films. After annealing at the temperature higher than 450 °C predominant MoO2 appears in the multilayered MoO3/Cu thin films. Meanwhile, CuO and Cu2O are also present in the thin films. The formation mechanism of reduced molybdenum suboxide can be explained by the oxygen-vacancy generation reaction or the reduction of MoO3 to MoO3-x via the inter-diffusion at the MoO3/Cu interfaces. The band gaps and conductivity activation energies of multilayered MoO3/Cu thin films decrease as the annealing temperature increases, in which the smallest band gap of ~2.05 eV and activation energy of ~0.02 eV for the MoO2 thin films are found. Our results open a new road to broaden the application of reduced molybdenum suboxides as a back contact material for CdTe solar cells.

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.

The carrier lifetime in CdTe is strongly limited by the nonradiative recombination via defects. Here, deep level defects in CdTe thin-film solar cells are revealed by transient photo-capacitance (TPC) measurement. A broad defect band centered at 1.07 eV above the valance band is identified at 90 K. The defect signal is reduced with the insertion of the CdSe layer between the CdS/CdTe heterojunction. The TPC signals are rapidly quenched with increased temperature, which suggests that this deep level defect is highly possible to act as an effective recombination center. Based on the thermal quenching model, the activation energy (E a) of the defect is estimated to be ∼0.2 eV. With the configuration coordinate model, the temperature-dependent TPC signal and the corresponding electronic transition process can be well interpreted. All the observations strongly indicate that the introduction of Se atoms into CdTe is promising to suppress the formation of deep defects.

As the improvement in efficiency of CdTe solar cell becomes more and more difficult, it is very necessary to engage in research on CdTe solar cell with innovative structure or new materials. In this work, we first proposed a design idea of constructing cadmium telluride on silicon to form a CdTe/Si composite absorption layer and then achieving an innovative high efficiency solar cell with a basic structure of n-Zn1-xMgxO/p-CdTe/p-Si/Au. This kind of solar cell has the advantages of relatively high open-circuit voltage and large short-circuit current, because photons with a wavelength range of 825 nm–1100 nm can not be absorbed by CdTe with a bandgap of 1.5 eV while they can be absorbed by silicon with a bandgap of 1.12 eV, thereby extending the long-wave response of sunlight. Numerical simulation of solar cell was carried out by using SCAPS-1D software to study the impacts of materials parameters such as thickness, doping concentration, valence band offset (VBO) and interface state density of CdTe/Si on device performances. Results indicated that thinner CdTe and suitable thick Si were beneficial for the cell with high efficiency. Particularly, the interface states between CdTe and Si severely degraded cell performance, so an innovative CdSixTey layer was proposed for the first time to effectively reduce the lattice mismatch and modify the interface properties between CdTe and Si. Finally, the highest theoretical conversion efficiency of 28.36% accompanied by open-circuit voltage of 0.838 V, short-circuit current of 39.28 mA/cm2, and fill factor of 86.11% of solar cell with SnO2:F/Zn1-xMgxO/CdTe/CdSixTey/Si/ZnTe:Mo/Au structure was obtained by optimizing numerical simulation design.

Ohmic back contact is one of the keys to fabricate high efficient CdTe solar cells, as it can improve fill factor FF and open-circuit voltage Voc. In this work, antimony-containing reduced graphene oxide (RGO) was prepared and used as a back contact for CdTe thin film solar cells, in which antimony is an effective dopant for CdTe and RGO acts as a hole transport layer and diffusion barrier of antimony in the solar cells. Post deposition annealing was performed to activate the back contact layer and passivate the interface defect states. Electrical performance and apparent quantum efficiency characterization were performed to investigate device performance of CdTe solar cells with antimony-containing RGO back contacts. The results indicate that, the introduction of extrinsic doping near the CdTe back surface serves to reduce the back contact depletion width and enhance the built-in potential to enable the tunnelling of majority carrier holes through the barrier, and the RGO is beneficial for the formation of Ohmic back contact on CdTe.

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 introduction of selenium in the CdTe solar cells has been responsible for high performance CdTe thin film solar cells in recent years. It is an approach to form CdSexTe1-x alloys by the interdiffusion using precursor CdSe layer during the CdTe high-temperature deposition process. Nevertheless, the compositionally gradient CdSexTe1-x formed by the diffusion makes it difficult to absorb long-wavelength photons adequately. So close-spaced sublimation deposited CdSexTe1-x interlayer was incorporated in the CdTe thin film solar cells. It is found that 600 nm CdSexTe1-x absorber is useful to increase long-wavelength photons absorption and extend the long-wavelength QE response. Meanwhile, the synergetic effects of the primary absorber deposition processing on CdTe solar cell performance were investigated. The substrate temperature of CdTe deposition has an obvious impact on the cell efficiency. The much higher substrate temperature can efficiently gain larger grain size, increase the crystal quality and promote the interdiffusion of different semiconductor layers. These improvements can efficiently decrease the carrier recombination to obtain a much higher fill factor and open-circuit voltage.

Transparent MoOx thin films with varied composition were successfully prepared by sputtering and the effects of oxygen contents on the composition stoichiometry, defect states, work functions, electrical and optical properties of MoOx films were systematically studied. These thin films were then utilized in cadmium telluride solar cells to act as back contact buffers. As compared with the CdTe solar cells with Au back contact, deteriorated performance was witnessed in those with MoOx buffers. The deterioration was demonstrated to be caused by the oxidation of CdTe surface, the large valence band offset and the insufficient work function. Finally, by optimizing the back contacts to form a CuCl/MoOx/ITO composite back contact, the efficiency was improved to 11.8%. This work demonstrates feasible approaches to prepare MoOx thin films with varied oxygen concentrations which could be easily applied to many other thin film solar cells and provide important indications in the preparation and optimization of the performance for bifacial devices.

There is always a surge of interest in compositional engineering to improve the performance of organic–inorganic halide perovskite (OIHP) solar cells among research communities. However, the role of dopant in OIHPs has not been clearly clarified so far. Relying on the slow growth of spaced-limited method, crystallization details of OIPH thin films can be amplified to explore the dopant distribution behavior easily. Herein, we optimized preparation conditions of spaced-limited method, and then conducted Bi3+ incorporation into MAPbBr3 single-crystalline thin films (SCTFs) to further explore its impacts from another angle. PTAA-modified substrate surfaces could accelerate the diffusion of precursor ions in the slit, which facilitated to obtain large area OIPH thin films. After Bi3+ incorporation, it’s easy to find that Bi3+ could gradually aggregate on the top surface of MAPbxBi1-xBr3 thin films to form a layer of brown materials (MAPbBr3 crystal grains containing high Bi3+ content). As Bi3+ concentration increased in precursor solution, Bi3+-based perovskite (MA3Bi2Br9) would finally separate. Bi3+ distribution behavior and growth mechanism of MAPbxBi1-xBr3 thin films can give more enlightenment for understanding the role of dopant ions in OIHPs for applications in modern electronics.

To meet the large-scale fabrication technology of perovskite solar cells in the future, a novel method is proposed herein to achieve an excellent and highly reproducible CH3NH3PbI3−xClx film based on a high concentration spinning process. Pinholes in the CH3NH3PbI3−xClx film were substantially reduced, leading to better uniformity and film coverage. The precursor ions and molecules promoted nucleation and growth while releasing by-products gradually, which was beneficial to continuous growth and crystallization of the perovskite film in high concentration conditions and then resulted in significantly enhanced optoelectronic characteristics and device performance. Up to 13.8% of power conversion efficiency had been achieved by employing the FTO/bl-TiO2/mp-TiO2/CH3NH3PbI3−xClx/Spiro-MeOTAD/Au device structure under AM1.5 global spectral irradiation (100 mW cm−2). This method offered an efficacious and simple strategy for a highly reproducible large-area fabrication process of low-cost perovskite solar cells.

Pulsed laser deposition (PLD) technique is suitable for the deposition of high-quality compound semiconductor thin films, and has been widely developed in recent years. However, pulsed laser deposition of CdS films has rarely been reported. In this work, we prepared CdS thin films using PLD. The effects of growth temperature on the PLD-CdS thin films were studied towards high-performance CdS/CdTe thin film solar cells. Results showed that the CdS film prepared at 400 °C has the best crystallinity and optical transmittance, while 200 °C is more suitable for the window layer of CdTe solar cells due to the highest energy conversion efficiency and the best short-wavelength response. CdCl2 annealing treatment was also employed on the 200 °C-deposited and 400 °C-deposited PLD-CdS layer. Annealing treatment further enhanced crystallinity, and obviously enlarged the grain size. Optical transmittance spectra showed that the band gap of the CdS films increased after annealing. Fermi level of CdS films shifted closer to the conduction band from XPS analysis. CdTe solar cells with annealed windows obtained further improved performance, including higher short-circuit current, open-circuit voltage and energy conversion efficiency.

The Cadmium telluride (CdTe) thin film has been prepared by physical vapor deposition (PVD), the Ar + O2 pressure is about 0.9 kPa. This method is a newer technique to deposit CdTe thin film in large area, and the size of the film is 30 y 40 cm2. This method is much different from the close-spaced sublimation (CSS), as the relevance between the source temperature and the substrate temperature is weak, and the gas phase of CdTe is transferred to the substrate by Ar + O2 flow. Through this method, the compact and uniform CdTe film (30 y 40 cm2) has been achieved, and the performances of the CdTe thin film have been determined by transmission spectrum, SEM and XRD. The film is observed to be compact with a good crystallinity, the CdTe is polycrystalline with a cubic structure and a strongly preferred (1 1 1) orientation. Using the CdTe thin film (3 y 5 cm2) which is taken from the deposited large-area film, the 14.6% efficiency CdS/CdTe thin film solar cell has been prepared successfully. The structure of the cell is glass/FTO/CdS/CdTe/graphite slurry/Au, short circuit current density (Jsc) of the cell is 26.9 mA/cm2, open circuit voltage (Voc) is 823 mV, and filling factor (FF) is 66.05%. This technique can be a quite promising method to apply in the industrial production, as it has great prospects in the fabricating of large-area CdTe film.

In this work, a composite window layer of the sandwich structure containing CdS/ZnS multilayer for CdTe thin film solar cell was designed. Two composite windows of this kind with 5 cycles and 8 cycles CdS/ZnS respectively were prepared by pulsed laser deposition, and finally were fabricated into CdTe-based thin film solar cell. SEM images show that the pulsed laser deposited composite window layers have good crystallinity. CdS and ZnS are layer-by-layer stacking together as the design. In comparison with CdS single-layer window, the composite windows have a blue-shift transmittance edge due to introduction of wide-bandgap ZnS, and show higher transmittance in the short-wavelength region. CdTe solar cells with the composite window obtain further improved performance, including higher short-circuit current (JSC) and energy conversion efficiency. Also, enhanced QE of CdTe solar cells with the composite window is observed in both short-wavelength and visible region. Meanwhile, some differences exist in the J–V and QE curves between the two composite window solar cells, indicating the volume proportion of ZnS may be an important factor that affects the performance of CdTe solar cell with the CdS/ZnS composite window.

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)).

In this paper, the effects of different CdCl2 annealing methods, including vapor annealing and dip-coating annealing, on the performance of CdS/CdTe polycrystalline thin-film solar cells are studied. After annealing, the samples are lightly etched with 1% bromine in methanol to remove surface oxides. Both annealing methods give CdTe polycrystalline thin films with good crystallinity and complete structure. For solar cells containing the annealed CdTe films, cell efficiency first increases and then decreases as the concentration of CdCl2 solution used for dip-coating annealing increases, and the optimized CdCl2 concentration is 12%. The uniformity of the performance of all cells is analyzed by calculating the relative standard deviation for each parameter. The uniformity of cell performance can be improved dramatically by dip-coating annealing instead of vapor annealing. Most notably, an appropriate concentration of CdCl2 (12%) acts as a protective layer that is conducive to realizing uniform high-performance CdS/CdTe solar cells. According to the location of depletion regions, the CdTe films treated by dip-coating annealing show a relatively low doping concentration, except for the sample treated with a CdCl2 concentration of 6%, which is consistent with the changes of short-circuit current density of the cells. It is believed that these results can be applied to the large-scale production of CdTe polycrystalline thin-film solar cells.

CdS thin film was used as a suitable window layer for CdS/CdTe solar cell, and the properties of CdS thin films deposited by pulsed laser deposition (PLD), chemical bath deposition (CBD) and magnetron sputtering (MS) were reported. The experimental results show that the transmittances of PLD-CdS thin films are about 85% and the band gaps are about 2.38–2.42eV. SEM results show that the surface of PLD-CdS thin film is much more compact and uniform. PLD is more suitable to prepare the CdS thin films than CBD and MS. Based on the thorough study, by using totally PLD technique, the FTO/PLD-CdS(150 nm)/CSS-CdTe solar cell (0.0707 cm2) can be prepared with an efficiency of 10.475%.

CdTe films have been prepared by close-spaced sublimation under different conditions. When CdTe is deposited at a low temperature, grains with a single predominant growth plane (111) adhere to the substrate and gather into scattered particles. With increasing deposition temperature, the number of CdTe grains on the substrate increases very quickly, the grains begin to form a quasi-continuous film, and (220), (311), (400), and (331) growth planes of CdTe begin to appear. When the deposition temperature and time are increased further, the CdTe grains begin to accumulate, the pin-holes formed initially begin to disappear, and grain boundaries with traces of layer growth can be observed. Different transmittance of samples of different thickness is clearly apparent but changes of the band gap, E g, of the CdTe films is negligible. XPS results suggest CdTeO3 is generated on the CdTe film surface as the deposition time is increased.

For high-efficiency perovskite solar cells (PSCs), interface engineering becomes critical for carrier collection from the active perovskite material to the transport layer. To enhance the power conversion efficiency (PCE), herein we demonstrate a novel method named surface plasma treatment on a mesoporous TiO2 electron-transport layer (ETL) to improve electron extraction and transport properties at the perovskite/TiO2 interface. According to the XPS results, the plasma treatment induced a partial reduction of Ti4+ to Ti3+ within the TiO2 lattice and increased the concentration of oxygen vacancies on the TiO2 surface. Ultraviolet photoelectron spectra (UPS) show that the Fermi level of TiO2 upshifts about 0.2 eV which may effectively promote carrier separation and transfer at the perovskite/TiO2 interface. In addition, these created donor levels of Ti3+ and oxygen vacancies donate extra electrons, increasing the conductivities of TiO2 films and which could further promote transport. The time-resolved photoluminescence spectra (TRPL) confirm that the decay time decreases dramatically from 656 ns to 235 ns after 90 s plasma treatment, which indicates a more efficient electron-transfer process. Based on all the above-mentioned results, a remarkable enhancement in cell efficiency was obtained, such that the average efficiency was improved from 11.5 % to 14.3 % under AM 1.5G irradiation (100 mW cm-2 ).

The present work was undertaken to provide an in-depth insight into a relatively new joining technique, the so-called laser pressure welding. To this end, the fundamental aspects of microstructural evolution occurring during welding of pure aluminum were studied. The microstructural changes were found to be relatively complex involving static recrystallization, melting, solidification and plastic deformation. The solidified grains were deduced to nucleate epitaxially on the recrystallized grains thus inheriting their crystallographic orientations. From thorough microstructural analysis, it was deduced that the solidification process initiated before rolling and thus the freshly crystallized material experienced a plastic strain.

Fluorine-doped Mg0.21Zn0.79O (MZO:F) thin films were successfully deposited on glass substrates at room temperature by radio frequency (RF) magnetron co-sputtering method with Mg0.21Zn0.79O, MgF2, and ZnF2 targets. Low resistivity (1.26 × 10-1 Ω⋅cm), high Hall mobility (3.55 cm2/Vs) and high carrier concentration (1.39 × 1019 cm−3) were simultaneously realized in the annealed MZO:F film. The effects of doping concentration and annealing temperature on the structural, morphological, electronic, electrical and optical properties of MZO:F films were systematically investigated in this study. XRD and XPS analysis confirmed that F atoms have entered into crystal lattices of MZO and acted as donors when they occupied O sites in the hexagonal lattice. Moreover, it was observed that both doping concentration and annealing temperature greatly affected the crystallinity, grain size, growth orientation and surface morphology of the MZO:F thin films. In addition, the optical gap changed dramatically with the F content and annealing temperature, which could be attribute to the Burstein-Moss effect accompanied by the effects of fluctuating potential arising from the randomly situated impurities.

Cd 1− x Zn x Te (CZT) has a band gap tailored continuously from 1.45 to 2.26 eV and is therefore a potential candidate for the top cell in tandem solar cell applications. In this paper, Cd 0.6 Zn 0.4 Te: Cu thin films were fabricated by RF magnetron sputtering from three targets (ZnTe, CdTe and Cu). X-ray diffraction patterns show that the as-deposited films were the cubic phase with a preferred (111) orientation. The strain formed in the Cu-doped Cd 0.6 Zn 0.4 Te thin films increased with increasing Cu concentration. All the films had a band gap of around 1.72 eV, but an apparent decrease of transmittance occurred in heavily doped ones.5.70 at% doped Cd 0.6 Zn 0.4 Te: Cu films presented only less than 10% transmittance. The conductivity of Cd 0.6 Zn 0.4 Te: Cu films at room temperature increased with Cu concentration in the range of 10 −4 ∼10 0 S cm −1 . The temperature dependence of dark conductivity for Cu-doped samples did not follow the Arrhenius behavior and a deviation appeared on the warming curve. The activation energy of the dark conductivity for doped and undoped CZT films was calculated between 0.15 and 0.80 eV. Finally, CdS/CZT junctions were prepared. These devices were found to indicate the photovoltaic effects. And the device performance was analyzed.

It is a reasonable way to increase power generation and reduce the expensive solar cell materials by combining low-cost concentrator and solar cells. The characterization of low concentration CdTe solar cell under standard test condition (STC) and monochromatic light were carried out. The application of concentrator significantly increases the power output of CdTe solar cell. The monochromatic I-V results suggest that the FF of CdTe solar cell was critically affected in the wave length range of 525 to 780 nm. Also the effect of the anti-reflective film on the low concentration CdTe solar cells were revealed, and the results imply that the anti-reflective effect is magnified mainly at the wave length range of 525 to 780 nm.