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Summary Perovskite solar cells (PSCs) have seen rapid advance in power conversion efficiencies (PCEs). However, the state-of-the-art PSCs still suffer from inhomogeneously distributed nonradiative recombination and carrier transport losses. Here, we report a promising evaluation strategy of combining the generalized optoelectronic reciprocity theorems and camera-based luminescence imaging techniques for PSCs. Excess lead chloride compositional engineering increases homogeneity and suppresses nonradiative recombination, leading to an external luminescence efficiency of 1.14% of devices (corresponding to a nonradiative voltage loss of 0.116 V). A favorable local and global carrier extraction property at maximum power point is also observed under moderate illumination level. As a result, we achieve a 25.49 cm2 perovskite solar module with a 17.88%-certified efficiency and a record fill factor over 78%. This quantitative and spatially resolved characterization is applicable at specific operating points, offering enormous potential for future real-time tracking of the lab-scaled devices and fast assessment of screening the large-area modules.

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).

Understanding the nature of photogenerated carriers and their subsequent dynamics in perovskites is important for the development of related materials and devices. Most ultrafast dynamic measurements on the perovskite materials were conducted under high carrier densities, which likely obscures the genuine dynamics at low carrier densities under solar illumination conditions. In this study, we presented a detailed experimental study of the carrier density-dependent dynamics in hybrid lead iodide perovskites using a highly sensitive transient absorption spectrometer. We found that the carrier lifetime was about a hundred nanosecond in the linear response range, representing sunlight excitation, which was much longer than under high carrier densities. We also elucidated that the fast carrier decay (

In recent years, perovskite solar cells (PSCs) have experienced rapid development and have presented an excellent commercial prospect as the PSCs are made from raw materials that are readily and cheaply available depending on simple manufacturing techniques. However, the commercial production and utilization of PSCs remain immature, leading to substantial efforts needed to boost the development of scalable fabrication of PSCs, pilot scale tests, and the establishment of industrial production lines. In this way, the PSCs are expected to be successfully popularized from the laboratory to the photovoltaic market. In this review, the history of power conversion efficiency (PCE) for laboratory-scale PSCs is firstly introduced, and then some methods for maintaining high PCE in the upscaling process is displayed. The achievements in the stability and environmental friendliness of PSCs are also summarized because they are also of significance for commercialization. Finally, this review evaluates the commercialization prospects of PSCs from the economic view and provides a short outlook.

Water transport in coal is a multiscale, multiphysical process that is affected by the coupling effect of multiple systems, such as pore and microfracture systems. In this study, numerical ...

The photovoltaic (PV) panels currently existed on market are laminated plate structures, which are composed of two stiff glass skins and a soft interlayer. Some panels are installed on the buildings and integrated as the components of the structures, such as wall and roof. In different locations, the installations of PV panels are different and the boundary conditions are not always simply supported. In this paper, the bending behaviour of PV panels with various boundary conditions is analysed and the influence of boundary condition is studied carefully. The Kirchhoff theory is adopted to build governing equations of PV panels under static force. A Rayleigh-Rita method is modified to solve the governing equations and calculate the static deformation and stress. Different boundary conditions usually require different assumptions of the deflection function, but a modified general function is developed in here to solve that problem. A theoretical solution is derived out and used to do the numerical calculation. The bending experiments of PV panels with two boundary conditions are used to verify the accuracy of the proposed solutions. Finally, the influence of different boundary condition is stated by comparing the numerical results and some guides for the PV panel installation are proposed.

Substantial improvement of the open-circuit voltage of thin film solar cells has been investigated by applying an electron reflector strategy. Cd1-xMgxTe has a strong potential as an electron reflector to keep minority carriers away from the CdTe back surface to reduce the back surface recombination. In this paper, SCAPS simulations were first used to investigate device performance for CdTe solar cells with the electron reflector layers. The theoretical results indicate that the ∼0.4 eV electron barrier height for CdTe solar cells with Cd1-xMgxTe (Eg∼1.85 eV) is sufficient to decrease the back surface recombination and improve device performance, especially the open-circuit voltage. Thus the variation of energy gap of the Cd1-xMgxTe thin films prepared by coevaporation as a function of x was investigated from the transmittance spectra. Then Cd1-xMgxTe (x∼0.3) thin films were used as the electron reflectors for the CdTe thin film solar cells. It is found that CdTe solar cells with Cd1-xMgxTe yielded open-circuit voltage of 804 mV and fill factor more than 70% after an 425 °C anneal, which is higher than those without Cd1-xMgxTe. The electron reflector in CdTe solar cells can effectively reduce the carrier surface recombination, thereby resulting in the increase of the fill factor and the open-circuit voltage.

Cd2SnO4-based CdTe solar cell is a potential technology to fabricate low cost and highly efficient thin film photovoltaic modules due to the excellent optical and electrical properties of Cd2SnO4 conductive transparent layer. However, the detailed research on patterning process is still deficient. In the present work, we developed laser scribing techniques to pattern the Cd2SnO4 thin film and the functional layers on top of the transparent conductive layer. By modifying the process and precisely adjusting the average energy density, the technique was further optimized to remove the upper layers completely without inducing any damage to the Cd2SnO4. The laser scribing process eliminates the exaggerated current density of CdTe solar cells contributed by the light absorption of the residual upper layers and as a result, device performance of the laser scribed cells could be precisely characterized. Besides, the isolative laser scribing of Cd2SnO4 layer and layers on top of Cd2SnO4 (window layer, absorption layer, back contact and metal electrode) is equal to the so-called P1, P2 and P3 steps in thin-film PV module production, which suggests that the whole set of laser scribing technique is applicable to the mass production of the Cd2SnO4-based CdTe solar cell modules.

Copper has been introduced in CdTe solar cell manufacturing for a long time and is critical for achieving high performance devices. In this work, CuCl thin films were prepared by vacuum thermal deposition and then used as a buffer layer with a thermal annealing treatment for activation in the CdTe solar cells. The results indicate that Cu and Cl diffused into the CdTe absorber which was beneficial for doping and copassivation. The carrier density for CdTe solar cells in the vicinity of the pn junction was significantly improved from 6.1 × 1013 to 4.3 × 1014 cm−3, and Voc was increased by >70 mV. The cell with the CuCl thin films was more uniform and revealed higher photocurrent response than the reference cell. The results also indicate that the formation of ohmic back contacts to CdTe solar cells due to the presence of the CuxTe (Cu7Te4) thin films. An optimal device with open circuit voltage of ~820 mV, and fill factor of ~72% and efficiency reaching 16.69% was obtained by the control of the copper concentration and the thermal activation conditions of the CuCl buffer layer.

A low-resistance and stable back contact to p-type CdTe semiconductor is crucial for the high-efficiency CdTe solar cells. In this work, ZnTe/Cu1.4Te bilayer alloys were fabricated by evaporation to form a new back-contact configuration for CdTe solar cells due to the well-matched interfacial property of ZnTe and the heavily p-doped property of Cu1.4Te. The devices with single layer or double layers have an effective doping level from ∼5 × 1013 to ∼3 × 1014 cm−3, resulting in the improvement of device performance and apparent increase in quantum response in the CdS and CdTe regions, compared to the devices with only Au. Device performance demonstrates lower Schottky barrier and less carrier recombination for CdTe solar cells with ZnTe/Cu1.4Te than that for the cells with Cu or Cu1.4Te due to a better modification of the band structure. Time-resolved photoluminescence and dark capacitance-voltage measurements indicate the introduction of Cu or single Cu1.4Te layer creates recombination centers to reduce the minority carrier lifetime from 100.9 to 78.7 ns and compensate net carrier concentration. The insertion of ZnTe buffer layers effectively prevents Cu diffusing to decrease recombination defects, resulting in longer minority carrier lifetime of 86.7 ns and higher carrier density, due to a well-matched interfacial property that is roughly 5% lattice mismatch at the CdTe/ZnTe interface. Finally, cell efficiency of >15%, open circuit voltage of >810 mV and fill factor of >73% for CdTe solar cells with an area of 0.24 cm2 have been achieved. Accelerated aging tests show the stability of the cells over time is also improved by the incorporation of the ZnTe buffer layer.

Plasmonic metal-semiconductor nanostructures endow them with an enormous potential application in photocatalysis, however, the uniform deposition of metal NPs as small as a few nanometers remains a challenge. Here, we demonstrate the effectiveness of two-step polymer-network gel process in the synthesis of Ag-ZnO nanocatalyst with superior photocatalytic properties. Because of uniform distributed Ag NPs, large specific surface area and abundant surface oxygen vacancies, the Ag-ZnO nanoparticles exhibit a super high photocatalytic efficiency in comparison to pure ZnO nanoparticles. The efficiency can be further improved by optimizing the external factors, such as catalyst dosage, ambient temperature and initial solution pH. Good stability and practicability indicate its potential application in environmental purification. Our work does not only provide a feasible strategy for the synthesis of high property Ag-ZnO nanophotocatalysts, but also enriches the understanding of metal-metal oxide nanostructures.

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.

Intrinsic organic–inorganic metal-halide perovskites have shown widespread applications in optoelectronic devices. Also, controllable doping is a very convenient route to tailor the performance of ...

Terahertz emission by ultrafast excitation of semiconductor/metal interfaces was found strongly enhanced by plasmon resonance. Here, a three-dimensional nanoporous gold (NPG) was used to form semiconductor/metal compound with cadmium telluride (CdTe). We investigated the specific impact of surface plasmon from randomly nanoporous structure in the ultrafast optoelectronic response for THz generation, and observed a THz amplitude enhancement around an order of magnitude from CdTe on NPG compared to that from CdTe on silicon. Moreover, the plasmon enhancement for THz emission from NPG is stronger than that from gold film, indicating that randomly nanoporous structure is also effective for plasmonic enhancement in THz band.

In this work, CdS thin films were deposited on glass/fluorine-doping tin oxide (FTO) substrates by low-cost chemical bath deposition (CBD), followed by annealing with CdCl2-doping (Cl-doping) to fabricate resistive-type photodetectors (PDs) with a vertical structure of glass/FTO/CBD-CdS:Cl/electrode. The effect of annealing with Cl-doping (AwCl) on the various properties of films and the photodetection performance of PDs were systematically characterized by special testing methods. The results revealed that the surface morphology and crystal structure of CBD-CdS:Cl films were improved, accompanied by an enhancement of hexagonal phase (002) crystal plane (wurtzite structure), and the optical bandgap of films can be adjusted between 2.43 and 2.26 eV while the electron activation energy of the films was reduced from 75.9 to 10.3 meV after AwCl. Furthermore, the light responsivity of CBD-CdS:Cl PDs were 0.57, 0.59 and 1.67 A/W under 365, 400 and 530 nm illumination at a bias of −2.0 V, respectively, and the detectivity of photons at corresponding wavelengths were 3.7 × 108, 3.9 × 108 and 1.08 × 109 Jones. Meanwhile, the PDs showed optimized repeatability and improved sensitivity under periodic illumination. The above results demonstrated that the CBD-CdS:Cl PDs with a vertical structure developed in this work had good detection performance at certain characteristic wavelengths.

Facile, convenient and low-cost processes, including a chemical hydrothermal method and impregnation technique, were demonstrated to fabricate a self-powered ZnO nanorod array/CuSCN/reduced graphene oxide (rGO) ultraviolet photodetector. ZnO nanorods (NRs) were fully filled and encased by the CuSCN layer, in which CuSCN acts as the primary hole-transport layer and an electron reflection layer, blocking the electron transfer towards the Au electrode and reducing the electron–hole pair recombination. After annealing, this encapsulated structure further reduces the surface state defects of ZnO NRs, which can isolate the electron exchange with oxygen in the air, dramatically reducing the rise and fall time; it also forms a p–n junction, providing a built-in electric field to improve the photoresponse without applying external power. The rGO layer was coated on the surface of CuSCN as the secondary hole-transport layer and then annealed, which could effectively block Au from entering CuSCN and contacting ZnO along cracks and holes during vapor deposition, avoiding the formation of leakage channels. Furthermore, due to the ultra-high carrier mobility and the increase in work function after Au doping, the functionalized graphene could reduce the valence band shift, which is beneficial to enhance hole transport. Meanwhile, rGO obstructs the undesired barrier formed by electrical potential-induced reaction of Au with thiocyanate anions. Finally, the ZnO NR/CuSCN/rGO ultraviolet photodetector exhibits a significant enhancement in device performance (responsivity: 18.65 mA W−1 at 375 nm under 65 mW cm−2 illumination, rectification ratio: 5690 at ±1 V), which is better that of than ZnO NR/CuSCN structure (10.88 mA W−1, 10.22 at ±1 V) and maintains the 100 ms response time.

Interface engineering is imperative to boost the extraction capability in perovskite solar cells (PSCs). We propose a promising approach to enhance the electron mobility and charge transfer ability of tin oxide (SnO

CdTe devices with CdTe and CdTeSe/CdTe as absorber layer were fabricated. The highest short circuit current density reaches 28.73mA/cm2 of CdTeSe/CdTe device. Besides, defects of devices with different absorber layers were investigated using admittance. A shallow defect with activation energy of 0.09eV was only detected in CdSeTe/CdTe device, which may assign to the hydrogenic defects in CdSeTe alloy. A defect with activation energy of 0.34eV was detected in both devices which might relate to the native impurities. And the defect with activation energy of 0.55eV was only observed in CdTe only devices. Overall, Se is significant to reduce defects in CdTe.

When integrated photovoltaics into building windows, the solar cells will absorb a fraction of solar radiation that hit on the window surface to generate electrical power and thus obstruct the solar energy and natural daylight that would have penetrated into inside space. In this paper, a window system integrated with thin film CdTe solar cells with 10% transparency was electrically characterised by Sandia model. The annual energy performance of a typical office with this PV window applied to different facade design was investigated using EnergyPlus under five typical climatic conditions in China. The dynamic daylight performance of the office has been assessed using RADIANCE. The result shows that when compared to a conventional double glazed system, the application of PV window can result in significant energy saving potential if the office has a relative large window-to-wall ratio (i.e. WWR≥45%). The simulation results also show that this PV window offers better daylight performance than conventional double-glazing.

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 .

When integrating photovoltaics into building windows, the photovoltaic glazing modules inhibit the function that glass performs, with the additional function of energy production. Semi-transparent Photovoltaic (STPV) glazing will absorb part of the solar radiation incident on the window surface to generate electrical power. In turn, this affects the overall solar energy and natural daylight penetrating into the indoor space. Various factors determine the building energy performance and indoor comfort level as a result of adopting STPV glazing. The factors regarding window design alone (window size, PV glazing coverage ratio and PV glazing placing position) require rigorous study. In this paper, an innovate model (combined optical, electrical and energy model) was developed to comprehensively evaluate the performance of an office equipped with STPV window and firstly analyse the effect of window design on overall energy efficiency. A double-glazing unit integrated with thin film CdTe solar cells with 10% transparency was electrically characterised by Sandia Array Performance Model (SAPM). The annual energy performance of a typical office served by window integrated STPV glazing was investigated through EnergyPlus simulation for various window designs under five typical climatic conditions in China (using weather files of Harbin, Beijing, Shanghai, Guangzhou and Kunming for representation). The optical performance (defined by a Bidirectional Scattering Distribution Function) of this STPV glazing was also obtained using a ray-tracing technique. Then, the annual daylight performance of the porotype office was assessed using RADIANCE. We found that when compared to a conventional double-glazed system, the application of PV window can result in considerable energy saving if the office has a relatively large window-to-wall ratio (i.e. ≥ 45%), while the position of placing STPV glazing has significant influence on the lighting energy consumption. In the specific climates under test, the optimal design scenario of applying window integrated PV can result in a reduction in energy consumption of up to 73%. The simulation results also show that this PV window offers better daylight performance than conventional double glazing and effectively reduces the possibility of glare.

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.

We studied the impact of in situ post-growth annealing process on cadmium telluride (CdTe) polycrystalline thin film in this work. Samples of different annealing times have been characterized by x-ray diffraction (XRD) and a scanning electron microscope (SEM). The optoelectronic properties of CdTe film were deeply studied with light I–V testing, external quantum efficiency (EQE) and photoluminescence (PL)/time-resolved photoluminescence (TRPL) measurements. It is found that the in situ post-growth annealing treatment has a great effect on cadmium sulfide (CdS)/CdTe intermixing as well as interface pinholes. Elementary correlations between annealing time, film and junction morphology, carrier lifetime and device performance were investigated, and the annealing time turns out to be crucial to CdTe device performance. Solar cells with CdTe polycrystalline thin film annealed in situ at 550°C/550°C for 10 min show the best performance. With the help of precisely controlled annealing time, better CdTe film microstructure and morphology can be realized after in situ post-growth annealing.

Organic-inorganic hybrid perovskite single-crystalline thin films (SCTFs) are promising for enhancing photoelectric device performance. One key aspect is to be able to synthesize SCTFs with large surface areas. Here, we investigated the formation of MAPbBr3 SCTF by space-limited inverse temperature crystallization method. It was found that the weak wetting substrate could reduce friction force and promote precursor ion diffusion, which enabled a continuous growth of the thin perovskite single crystal along in-plane direction. SCTFs could be obtained at the initial stage of film growth and we also observed some signs of island growth model. Pyramid-shaped islands formed first and then converged to achieve top surface growth of SCTFs. After further growth, the precursor ion concentration near the SCTF gradually decreased. The lateral crystal growth was limited by the inefficient and anisotropic long range transportation of precursor ions along the micrometer-size or nanometer-size gap, which resulted in transformation of SCTFs into polycrystalline films. Low ion diffusion in the narrow gap is still the main constraint for the preparation of the larger and thinner SCTFs.

MoOx: Cu thin films were deposited by thermal co-evaporation. The copper atoms prevented MoOx thin films growing along or perpendicular to the substrates, resulting in the decrease of the crystallinity. The energy band gaps for the films decreased from 3.22 to 2.29 eV with the increase of Cu concentration from 0 to 20 at%. Owing to the formation of the oxygen vacancies, MoOx thin films were n-type semiconductors. As MoOx thin films were doped with Cu, the films also showed the characteristics of electronic conduction. In contrast to the difference between the Fermi level and the bottom of conduction band was 0.27 eV for MoOx thin films, a strong hybrization among the O 2p, Mo 4d, and Cu 3d states occurred in the Cu-doped MoOx thin films, thus the electrons occupied the anti-bonding d-d* band and the Fermi level was shifted within the conduction band. With the use of MoOx as a back contact buffer layer, performance of the CdTe solar cells was mainly improved by the reduced Schottky barrier, which is ascribed to the presence of the defect states. CdTe solar cells with Cu-doped MoOx thin films demonstrated higher efficiency (~14.63%) than those with undoped MoOx or without a back contact buffer in our work, which results from the enhancements in the open circuit voltage (~830 mV) and fill factor (~72.7%) due to the zero barrier in the MoOx: Cu thin films. Therefore, MoOx: Cu buffer layer is a promising contact material for CdTe solar cells.

Transport efficiency ( ${f_T}$ ) maps of photon-generated current from the junction to the terminal are demonstrated in CdTe solar cells, based on luminescence images and a recent reciprocity theorem. Current transport efficiency maps directly reveal the local electrical losses distribution at different working points, which help to understand the main detrimental mechanisms in CdTe cells. Electroluminescence and photoluminescence imaging measurements are used to distinguish and discuss the localized defects as well. The validity of this luminescence-derived method is successfully verified by comparison with simulation and standard electrical measurements. The diode-like shunts, which rob currents from nearby areas, cause significant decreases of local ${f_T}$ , while the effect of series resistance depends on the terminal current and dominates the additional applied voltage when operating over V OC.

The introduction of annealing treatment in CdCl2 atmosphere has been demonstrated to be an effective method in improving the efficiency of CdTe solar cells. Kelvin Probe Force Microscopy (KPFM) was used to study the effect of the CdCl2 treatment process by spatially resolved imaging of the surface contact potential difference (CPD). The results indicated that the grains were spatial depleted by grain boundaries (GBs). The quantitatively CPD distribution at GBs was analyzed by Gaussian fitting. During annealing process the carrier density was decreased and the electronic properties of the GBs were modified. The electronic structure changes resulted from the CdCl2 treatment at GBs were put forward to explain the efficiency enhancement in device performance. The results suggested that GB depletion regions were narrowed down and barrier height at the GBs was also significantly decreased. Therefore the carrier transport can be enhanced. A GB model including the electron traps was introduced. It was found that the barrier height at GBs can reach the maximum value at a specific hole density.

A low electric resistive and stable ohmic back contact are crucial to the commercial application of CdTe solar cells. In this study the Sb2Te3 thin film is employed as a buffer layer in the back contact of CdTe solar cells. The Sb2Te3 thin films are deposited at different substrate temperature by pulsed laser deposition and then characterized to investigate the thin film properties, firstly. Hall measurements shows the Sb2Te3 thin film presents strong p-type semiconductor features with high Hall mobility and carrier concentration. CdTe solar cells with Sb2Te3 buffer layer in different layer thickness and deposition temperature are fabricated to obtain the optimal experiment conditions for device performance. The dark J-V curve of CdTe solar cell with Sb2Te3 buffer layer exhibits a typical diode curve without roll-over phenomenon. An insertion of Sb2Te3 buffer layer eliminates the Schottky barrier resulting in remarkable enhancement of open circuit voltage, short-circuit current and fill factor. Besides, the external quantum efficiency gets improvement in almost all of the absorber wavelength compared to the cells with Au-only contact.

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 BiCl3 aqueous solution using hydrazine hydrate. The doping concentration of bismuth was varied by controlling the mass ratio of GO/BiCl3. 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.

CdSe film is noteworthy for its application in CdTe solar cells. In this paper, the crystal structure, surface profile and optical properties of CdSe films deposited at 25 °C, 200 °C, 250 °C, 300 °C and 350 °C by magnetron sputtering are investigated by XRD, SEM, AFM and an UV–VIS spectrometer. XRD patterns show that CdSe films deposited at 200 °C and 250 °C have cubic structure, which hasn’t been reported so far for sputtered CdSe films. CdSe films deposited at 300 °C and 350 °C are hexagonal. Then CdSe films with different substrate temperatures (25 °C, 200 °C, 250 °C and 300 °C) were used as the window layer for CdTe solar cells. CdSe/CdTe device with CdSe film deposited at 250 °C reaches the highest efficiency. Quantum efficiency (QE) was enhanced in the range of 300–510 nm and 830–900 nm for CdSe/CdTe device (CdSe film deposited at 250 °C) compared to CdS/CdTe device while in the range of 510–830 nm, QE of CdSe/CdTe device was lower than that of CdS/CdTe device indicating an inferior junction between CdSe and CdTe. The results also suggest that CdSe deposition temperature influences the film structure and further to the interfusion between CdSe and CdTe which has a significant effect on device performance.

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.

SnO2: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.

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.

Ba(Gd1-xYx)0.78F5: 20 mol% Yb3+, 2 mol% Tm3+ (0 ≤ x ≤ 1.0) solid solution nanocrystals were successfully synthesized via a facile hydrothermal method, the obtained crystals were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), the transmission electron microcopy (TEM), energy dispersion spectrometry (EDS), photoluminescence (PL) as well as vibrating sample magnetometer (VSM), respectively. The influences of the concentration of yttrium ion (Y3+) on the microstructures, upconversion (UC) luminescent and magnetic properties of the Ba(Gd1-xYx)0.78F5: 20 mol% Yb3+, 2 mol% Tm3+ samples have been deeply investigated. XRD results showed that all the Ba(Gd1-xYx)0.78F5: 20 mol% Yb3+, 2 mol% Tm3+ crystals are continuous solid solution possess a pure cubic phase structure. SEM and TEM results revealed that all the obtained crystals are quasi-spherical nanocrystals with a diameter ranging from ∼55 nm to ∼240 nm, and the doping of Y3+ ion can inhibit the grain growth. PL spectra indicated that all the samples exhibit main blue emission centered at 478 nm ascribed to 1G4→3H6 transition of Tm3+ ions, and its UC emission intensity initially increases and then notably decreases with increasing content of Y3+ ion, giving the maximum at x = 0.8. VSM results showed that all the samples present benign paramagnetism in the magnetic range of −30 to 30 kOe at 300 K due to no coercivity or no remanence. Our results confirm that the UC luminescence properties of the Ba(Gd1-xYx)0.78F5: 20 mol% Yb3+, 2 mol% Tm3+ nanocrystals can be effectively modulated through the replacement of Gd3+ ions by Y3+ ions, which also can provide a relatively clear understanding of the formation process and the enhancement mechanism of UC emission for other rare earth polyfluoride solid solution nanocrystals.

Reflection loss is essential factor to limit the efficiency of all of photovoltaic devices. Glass substrate that with no trapping mechanism to reduce the reflection of light as most CdTe commercial thin film solar cells are manufactured. The absorption band gap of CdTe devices is 387–850 nm, to minimize the losses, a broadband anti-reflection coating that its transmittance must as high as possible at 390–850 nm is designed with TFCALC modeling software and deposited with sol-gel method and dip-coatings technique on both sides of the glass substrate. See from the transmittance spectrum of broadband anti-reflection coatings (BARCs) is more than 98% at the band of 390–870 nm which is the same as the band gap of CdTe photovoltaic cells and its maximum transmittance is 99.70%. In addition to matched band and high transmittance, the durability of BARCs is crucial for applying on CdTe devices. It presents that BARCs that uses trimethyl chlorosilane (TMCS) to optimize the hydrophilic of the surface of BARCs is relatively stable from the examination of Contact angle and Environmental include damp heat, ultraviolet radiation and light-tact. The BARCs can well apply on CdTe modules that the optical property of BARCs is not affected by the preparation process of CdTe solar cell with simulation.

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.

Tungsten-doped indium oxide films were deposited by reactive plasma deposition using a low doped target in pure argon atmosphere at room temperature. Post thermal annealing was conducted in different atmospheres in the range of 150 °C–250 °C to improve the properties of films. The structural, electrical and optical properties of IWO films with different annealing conditions have been investigated. It is found that crystallization after annealing is an effective way to improve the mobility. The mobility of the polycrystalline films is much greater than amorphous films. And the ordered structure is conducive to interstitial oxygen and oxygen in the atmosphere to fill the oxygen vacancies, leading to the decrease of the carrier concentration and a further increase of the mobility. We have prepared IWO thin films with the carrier mobility (up to 83 cm2V−1s−1), even if as-deposited films had a relatively low carrier mobility (∼30 cm2V−1s−1). The optical transmittance of IWO films maintains 89% and 84% in visible and near-infrared regions, respectively. The mobility of IWO films is found to depend on the manufacture of the source target and the highest mobility of 120 cm2V−1s−1 has been reached.