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[Display omitted] • CH 3 NH 3 Pb(I 1-x Br x) 3 perovskite thin films are successfully applied as copper-free back contact layers for CdTe solar cells. • The facile deposition process of back contact layers. • The uniformity of CdTe solar cell is improved after applying CH 3 NH 3 Pb(I 1-x Br x) 3 back contact layers. • CdTe solar cell with a CH 3 NH 3 Pb(I 1-x Br x) 3 back contact layer exhibits good stability. In this study, bromide-iodide lead perovskite (CH 3 NH 3 Pb(I 1−x Br x) 3) thin films were fabricated and applied as copper-free back contact layers for CdTe solar cells. The results reveal that the open-circuit voltage (V oc) and fill factor (FF) of the CdTe solar cells are greatly enhanced by the utilization of perovskite back contact layers. This is mainly due to the evidently reduced charge transportation barrier at the back contact, which is verified by temperature-dependent current–voltage (J-V-T) and apparent quantum efficiency (AQE) measurements. Specifically, after the application of perovskite back contact layer, the best-performing device shows 15.80% improvement in efficiency (from 10.82 to 12.53%), with V oc and FF increasing by 3.94% and 6.91%, respectively. Besides, the overall uniformity of the solar cells is also improved by the perovskite back contact, suggested by laser beam induced current (LBIC) results. Further simulation results confirm the experimental results and clarify the optimized cell performance by perovskite back contact layer in terms of both energy band alignment and charge carriers' recombination. In addition, in the simulation section, we have also investigated the effect of the bandgap, thickness and doping level of perovskite and the doping level of CdTe on the cell performances. The experiments and the numerical simulation reported in this work suggest perovskite a potential copper-free back contact layer for the fabrication of efficient CdTe solar cells. [ABSTRACT FROM AUTHOR]

Flexible thin-film solar cells are important for their advantages in many aspects, and aluminum antimonide (AlSb) can be used as an absorbent layer in thin-film solar cells. However, its deliquescence limits its practical use. In this work, AlSb films were prepared by radio frequency (RF) magnetron sputtering on stainless steel flexible substrates. A flexible conformal coating membrane using acrylic resin was deposited on the AlSb films and its deliquescence prevention effect was verified. It was found that after conformal coating treatment, the deliquescence of the AlSb film was effectively stopped. The bare AlSb films and the Ni/AlSb/acrylic resin/Ni multilayer films were exposed to ambient air at the same time under the same conditions for lengths of time ranging from 1 min to 60 days. After 60 days, the bare AlSb film experienced significant deliquescence, such that the film was completely destroyed. However, the Ni/AlSb/acrylic resin/Ni multilayer films did not exhibit deliquescence. [ABSTRACT FROM AUTHOR]

Sb 2 Se 3 , an emerging promising binary compound semiconductor, was prepared at different substrate temperatures by pulsed laser deposition for thin film solar cells for the first time. In this work, CdS and Sb 2 Se 3 films were subsequently deposited by pulsed laser deposition to simplify the process. Film properties and device performance, closely related to the substrate temperature, were characterized by thermal gravimetric analysis, X-ray diffraction, UV–Vis–NIR spectrophotometer, scanning electron microscope, light and dark current density-voltage, external quantum efficiency and capacitance-voltage, respectively. Results indicate that Sb 2 Se 3 solar cells film deposited at 500 °C is better, with a better efficiency of 3.58%. Furthermore, SnO 2 high resistive layer was introduced into Sb 2 Se 3 solar cell to improve the junction quality, leading to a champion device efficiency of 4.41%. Image 1 • CdS/Sb 2 Se 3 bilayer was deposited by pulsed laser deposition for the first time. • Effects of substrate temperature on film properties and device performance were studied. • Sb 2 Se 3 film deposited at 500 °C is more suitable for Sb 2 Se 3 solar cells. • Champion efficiency of 4.41% was achieved due to the insertion of SnO 2 layer. [ABSTRACT FROM AUTHOR]

Developing a good back contact material is important for high efficiency CdTe solar cells. In this work, the graphite oxide (GO) was prepared by the Hummers method through liquid oxidization, and the Bi-doping reduced graphene oxides (Bi@RGO) with different concentrations were synthesized by a chemical reduction of GO and BiCl 3 aqueous solution using hydrazine hydrate. The doping concentration of bismuth was varied by controlling the mass ratio of GO/BiCl 3 . The peaks of bismuth and RGO can be easily observed in the X-ray diffraction patterns. Both Raman spectra analysis and infrared spectra analysis also show that RGO is reduced successfully. Transmission electron microscopy shows Bi nanoparticles are entrapped inside the flake-like RGO. Furthermore, Bi-containing RGO/Au system was used as a back contact to CdTe thin film solar cells. The devices with Bi-containing RGO layers were fabricated and their photovoltaic characteristics such as short circuit current density, open circuit voltage, fill factor and efficiency were obtained. The results illustrate that Bi@RGO improves the hole collection ability, and supplies an active Bi diffusion source for the absorption layer, thereby enhancing CdTe solar cell performance. [ABSTRACT FROM AUTHOR]

Sb 2 S 3 has a unique one-dimensional structure-composed (Sb 4 S 6) n ribbons leads to strong anisotropic carrier transport characteristic: carrier transport along the (Sb 4 S 6) n ribbon is more efficient than other ribbons. Therefore, it's crucial to control the direction of grain growth along the (hk1) orientation. In this work, the close space sublimation method was utilized to fabricate Sb 2 S 3 thin films with a systematic al regulation of substrate temperature. The results demonstrate that optimized Sb 2 S 3 thin film presented preferred orientation at the direction of (hk1). The champion device based on Au and Ni electrodes achieved a power conversion efficiency (PCE) of 3.06% and 1.69%, respectively. Schematic diagram of the close space sublimation system. [Display omitted] • The (hk1)-oriented Sb 2 S 3 thin films were prepared by close space sublimation method. • Study of the effect of different substrate temperatures on the structure and morphology of Sb 2 S 3 thin films. • Solar cells with structure of FTO/TiO 2 /CdS/Sb 2 S 3 /Ni were fabricated. • Ni was firstly used as the electrode for Sb 2 S 3 solar cells. [ABSTRACT FROM AUTHOR]

AlSb is a new type of optoelectronic material with wide potential application prospects, but the applications of AlSb thin films for solar cells were few reported before, owing to the intrinsic drawbacks of deliquescence for AlSb. In this work, four types of AlSb/Sb stacks were fabricated by using pulsed laser deposition: (1) AlSb/Sb (5 nm), (2) AlSb/Sb (10 nm), (3) AlSb/Sb (15 nm) and (4) the in situ annealed AlSb film covered with Sb film which thickness is 15 nm. The experimental results indicate that the thicker the Sb layer deposited on the surface of the AlSb film is, the lower the degree of deliquescence will be. XRD measurements showed that the AlSb/Sb stacks were not deliquesced completely after exposed to air for 48 h. The EDS spectrum suggested that the percentage of oxygen atoms in the annealed AlSb film covered with Sb (15 nm) was smaller than the unannealed. The SEM morphology analysis revealed the deliquescence of AlSb film: the local film deliquesced to form sand inclusions first, after then the gradual increased of the sand inclusions lead to all deliquescence of the crystalline AlSb. [ABSTRACT FROM AUTHOR]

SnO 2 :F (FTO), as a kind of transparent conductive oxide (TCO), exhibits excellent transmittance and conductivity and is widely used as transparency electrodes in solar cells. It’s very important to modifying the surface of FTO for it plays a critical role in CdTe solar cells. In this study, modifying effects of oxygen plasma on FTO was investigated systematically. Oxygen plasma treatment on FTO surface with ion accelerating voltage ranged from 0.4 kV to 1.6 kV has been processed. The O proportion of surface was increased after ion implantation. The Fermi level of surface measurement by XPS valance band spectra was lowered as the ion accelerating voltage increased to 1.2 kV and then raised as accelerating voltage was elevated to 1.6 kV. The work function measured by Kelvin probe force microscopy increased after ion implanting, and it was consistent with the variation of Fermi level. The change of energy band structure of FTO surface mainly originated from the surface composition variation. As FTO conduction was primarily due to oxyanion hole, the carrier was electron and its concentration was reduced while O proportion was elevated at the surface of FTO, as a result, the Fermi level lowered and the work function was enlarged. It was proved that oxygen plasma treatment is an effective method to modulate the energy band structure of the surface as well as other properties of FTO, which provides much more space for interface and surface modification and then photoelectric device performance promotion. [ABSTRACT FROM AUTHOR]

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 Mg x Zn 1−x O (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 ( V oc ) 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 V oc . 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 CdSe x Te 1−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. [ABSTRACT FROM AUTHOR]

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 CuCl 2 solution treatment was used in this work to enhance the p-doping of CdTe. The carrier density of CdTe was increased from 4.72 × 10 13 to 1.11 × 10 14 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 × 10 14 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 Cu x Te 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 cm 2 were achieved. [ABSTRACT FROM AUTHOR]

ZnTe epitaxial layers with different crystalline quality were grown by molecular beam epitaxy. ZnTe:O was achieved by oxygen incorporation in ZnTe films using ion implantation. The proper concentrations of O ions attributed to the formation of the intermediate band which was approximately 1.88 eV above the valence band maximum. Pulsed laser melting was then carried out on the samples. ZnTe with high crystalline quality and appropriate concentrations of oxygen ions led to the improvements of absorption efficiency of the intermediate band. The results suggest that factors such as the crystalline quality and the dose of O concentration are important to achieve better ZnTe:O intermediate-band photovoltaic materials. The way we utilize to fabricate ZnTe:O intermediate band solar cell materials is applicable, and the position and intensity of O states could be well controlled. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 Cu 1.4 Te 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, ∼10 21 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. [ABSTRACT FROM AUTHOR]

Incorporating Se element into Cadmium telluride (CdTe)-based superstrate configuration solar cells have advanced impressively. However, molybdenum (Mo)/CdTe/CdSe substrate configuration devices remain relatively unexplored, and Mo foil oxidation behavior during the fabrication process is kept in the dark. This work investigates a fresh CdTe/CdSe substrate configuration solar cell using Mo substrates. Mo/CdTe/CdSe/ZnO/AZO/ITO solar cells have been fabricated, CdTe absorber layer was obtained by closed space sublimation (CSS) under ∼2000 pa pressure in varying Ar/O 2 flu ratio. The champion device had an efficiency of 3.87% with unintentional Cu-doping and back contact. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-Ray spectroscopy (EDS) were applied to study the properties of CdTe films. Before CdTe deposition, molybdenum oxide (MoO x) was generated while heating the Mo substrate in an oxygen-containing environment. This buffer layer plays a pivotal role in blocking non-Ohmic back contact analyzed by current-voltage-temperature (J-V-T) measurements. Molybdenum oxidation states were extensively studied to build the relationship with a solar cell device. Our findings indicated that different oxygen partial pressure had less relevance with the CdTe surface chemical environment but was incredibly relevant for Mo metal foil oxidation states. [ABSTRACT FROM AUTHOR]

In recent years, the power conversion efficiency (PCE) up to 20% was obtained based on CdTe solar cells consisting of Glass/SnO 2 : F/SnO 2 /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 SnO 2 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. [ABSTRACT FROM AUTHOR]

Abstract: Cd1−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, Cd0.6Zn0.4Te: 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 Cd0.6Zn0.4Te 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 Cd0.6Zn0.4Te: Cu films presented only less than 10% transmittance. The conductivity of Cd0.6Zn0.4Te: Cu films at room temperature increased with Cu concentration in the range of 10−4∼100 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. [Copyright &y& Elsevier]

Abstract: Bi2Te3 thin films were fabricated by vacuum co-evaporation and the properties of the films were investigated using X-ray diffraction, Hall measurements, and synchrotron radiation photoemission spectroscopy. The results indicate that p-type Bi2Te3 films, which have a work function of about 5.4eV and carrier concentration of the order of 1021 cm−3, are a rhombohedral phase with a strong (105) preferred orientation. A co-evaporated Bi2Te3 buffer layer was used for a back contact to CdTe thin film solar cells. C–V measurements, light and dark J–V measurements, and spectral response analysis also show that the p back contact has greatly enhanced cell performance. [Copyright &y& Elsevier]

CuSbSe 2 has been a potential absorber layer for thin film solar cells by reason of its attractive photovoltaic properties and environmentally friendly constituent elements. In this work, high-quality CuSbSe 2 thin film was prepared by pulsed laser deposition (PLD) and further in-situ annealing. Structural, morphological, compositional and optical properties of the unannealed and annealed films were characterized and compared separately. The results proved the existence of CuSbSe 2 , Sb 2 Se 3 and Cu 3 SbSe 3 in the unannealed film. With the rising of deposition temperature, the content of Sb 2 Se 3 increased significantly. Moreover, in-situ annealing at 350 °C can effectively reduce the Sb 2 Se 3 and Cu 3 SbSe 3 in the film. The atomic ratio of Cu:Sb:Se in the annealed film is estimated to be 25.45:26.29:48.27, basically consistent with the stoichiometry ratio of CuSbSe 2. Both annealed and unannealed CuSbSe 2 films revealed a high absorption coefficient greater than 104 cm−1. The optical band gap of the annealed film was about 1.15eV, which meets the requirements for the absorber layer of solar cells. •High-quality CuSbSe 2 thin film was successfully prepared by pulsed laser deposition •The effect of deposition temperature on CuSbSe 2 thin film prepared by pulsed laser deposition was explored •In-situ annealing was applied to reduce impurities and promote the formation of CuSbSe 2 •It would be helpful for the applications of CuSbSe 2 in solar cells in the future. [ABSTRACT FROM AUTHOR]

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 V oc. 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. [ABSTRACT FROM AUTHOR]

As an important functional film, tin dioxide (SnO 2) was widely used in the communities of gas sensors as well as solar cells. SnO 2 (110) and (100) surfaces were thought to be stable, and both could be easily obtained by common preparation method. The characteristics of SnO 2 surface were critical to the performance of devices when it was applied in solar cells, and the SnO 2 (100) surface had not been understood explicitly. A series of SnO 2 (100) surface models with different terminal atoms were built in this work and calculated by density functional theory (DFT) with GGA + U. SnO 2 (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. SnO 2 (100) surface terminated with single monolayer of O atoms was the structure with the least surface states. The real surface of SnO 2 was thought to be consisting of O terminal atoms mostly. The charge neutral level of SnO 2 (100) surface was thought to be 2.94 eV above the valence band. Image 1 • SnO 2 (100) with different terminal atoms was investigated systematically by first-principle calculations. • Surface states were origin from the ten monolayers of surface and showed different characters with different terminal atoms. • The real surface of SnO 2 (100) was mainly terminated with O, and surface states mainly from structure terminated with Sn. [ABSTRACT FROM AUTHOR]