Post-selenization Process Research Articles

Suppressing Se Vacancies in Sb2Se3 Photocathode by In Situ Annealing with Moderate Se Vapor Pressure for Efficient Photoelectrochemical Water Splitting.

Sb2Se3 emerges as a promising material for solar energy conversion devices. Unfortunately, the common deep-level defect VSe (selenium vacancy) in Sb2Se3 results in a low solar conversion efficiency. The post selenization process has been widely adopted for suppressing VSe. However, the effect of selenization on suppressing VSe is often compromised and even more VSe are induced due to defect-correlation. Herein, high-quality Sb2Se3 films are prepared using an unconventional selenization process, with precisely regulating in situ annealing Se vapor pressure. It is found that moderate Se vapor pressure annealing can efficiently suppress VSe by overcoming defect-correlation, as well as promotes grain growth and forms a better heterojunction band alignment. Consequently, the Sb2Se3 photocathode shows a high-level photocurrent of 19.5 mA cm-2 at 0 VRHE, an onset potential of 0.40 VRHE and a half-cell solar-to-hydrogen conversion efficiency of 1.9%, owing to the inhibited charge recombination, excellent charge transport and interface charge extraction. This work provides a significant insight to suppress deep-level defect VSe by adjusting Se vapor pressure for efficient Sb2Se3 photocathode.

Modifying back contact by silver to Enhance the performance of carbon-based Sb2S3 solar cells

Antimony sulfide (Sb2S3) has drawn significant attention due to its excellent photoelectric properties. However, the photon conversion efficiency of Sb2S3 solar cell is limited by its magnificent value band offset between absorber layer and carbon electrode. Herein, a back surface optimization strategy is developed to reduce the barrier at the back contact. By introducing Ag at back contact before post-selenization process, the Valence-Band Maximum (VBM) of Sb2S3 is elevated under the action of spin–orbit interaction between Sb-5 s orbit and Ag-d orbit, leading to improve the extraction of holes. Consequently, the electrical conductivity of the film undergoes a significant improvement, rising from 1.20 × 10-5 to 1.59 × 10-5 S/cm. Additionally, the film surface morphology is refined, exhibiting a reduction in roughness from 17.1 nm to 13.6 nm, which leads to less leak current generated. Finally, the device based on FTO/SnO2/CdS/Sb2S3/Carbon structure achieved the power conversion efficiency (PCE) of 5.51 %, representing a 16 % improvement compared to the device without Ag treatment.

A novel Se-diffused selenization strategy to suppress bulk and interfacial defects in Sb2Se3 thin film solar cell

In recent years, vacuum-based deposition of antimony selenide (Sb2Se3) thin films has garnered significant attention owing to its easy and impurity-free fabrication, along with exceptional power conversion efficiency (PCE). However, the necessary post-selenization process comes with a shortcoming of instigating buried Sb2Se3/molybdenum (Mo) back-contact interface defects. This study introduces a novel Se-diffusion post-selenization technique to precisely regulate the selenium reaction atmosphere, preventing void formation on the Sb2Se3 thin film surface and maintaining film quality for enhanced device efficiency. An optimized selenization condition with a precise Se precursor film thickness led to obtaining highly crystalline, preferentially (hk1) oriented, and large-grained Sb2Se3 films. Furthermore, a meticulous Se diffusion in Sb2Se3 film reduced the inevitable MoSe2 layer thickness at the Mo surface, thereby enhancing the quality of the back contact interface. The Sb2Se3 solar cell that was selenized to optimal level showed significant enhancements, raising the fill factor from 40.06 % to 45.12 % and improving the device efficiency from 2.89 % to 3.57 %. Our newly developed selenization strategy establishes a successful approach to regulate the Sb2Se3 film quality by addressing a crucial challenge in improving the efficiency of antimony chalcogenide solar cells.

Nanoarchitectonics of ternary NixCo1-xSe2 electrocatalysts on Ni-foams combined with Pt-loaded carbon clothes as the air-cathodes in Zn-air energy storage systems

BackgroundLarge-scale application of renewable energy with energy storage system is important for the reduction of influence on global warming effect without decreasing industrial activities. To develop an energy storage system is thus an important way for industrial application. MethodsTernary NixCo1-xSe2 electrocatalysts were prepared in an ethanol bath with reaction temperature of 70 °C in 10 min using a simple chemical synthesis method. Samples after post-selenization process as the electrocatalysts on nickel (Ni)-foams with Pt-loading carbon clothes were employed in Zn-air batteries. Significant findingsThe X-ray diffraction patterns of samples showed ternary NixCo1-xSe2 samples with high Se-vacancies. Therefore, the post-selenization process with temperature of 500 °C for 30 min was applied on these samples with various weights of Se powders. Samples as the electrocatalysts showed good stabilities in our homemade Zn-air batteries with the minimum voltage difference for oxygen evolution/reduction reactions of 0.91 V. Our cell with NiCo1-xSe2 electrocatalyst (Ni:Co:Se=0.21:0.29:0.50)@Ni foam + Pt-loading carbon cloth as the air-cathode showed the charge/discharge voltages of 2.05 and 1.08 V at charge/discharge current density of 10 mA/cm2, respectively, and could be applied in industrial energy storage system.

Eliminating cracking morphology of solution-processed CZTSSe absorbers by Sn-rich composition engineering

Sol-gel method has attracted widespread attention for fabricating highly efficient Cu2ZnSn(S, Se)4 (CZTSSe) solar cells. However, the volume shrinkage of the gel during the baking process will cause severe cracking of CZTSSe films, which results in shunt paths and significantly deteriorates device performance. Herein, an Sn-rich CZTS precursor is proposed to produce high-quality CZTSSe films, which could relieve the shrinkage forces in CZTS precursor film and compensate for Sn loss of CZTSSe absorbers during selenization process. The effects of Sn content on CZTS precursor compactness and the post-selenization process on the crystallization quality of CZTSSe films are thoroughly investigated. Furthermore, the formation of the MoSe2 interfacial layer and the SnSe2 secondary phase can be regulated efficiently. As a result, the separation and collection of carriers are greatly improved as the depletion region width (Wd) of the CZTSSe solar cell is broadened. And the difference between the activation energy (Ea) and band gap (Eg) has decreased, indicating that the carrier recombination loss caused by the deviated Sn content in CZTSSe films has been effectively reduced. Consequently, the efficiency of the CZTSSe device increased from 7.6% to 9.3% through Sn-rich composition engineering. This study elucidates the role of Sn content in the fabrication of high-quality CZTSSe films and advances the development of ambient air-processed CZTSSe solar cells.

Crystal Growth Promotion and Defect Passivation by Hydrothermal and Selenized Deposition for Substrate-Structured Antimony Selenosulfide Solar Cells.

Antimony sulfide-selenide (Sb2(S,Se)3) is a promising light-harvesting material for stable and high-efficiency thin-film photovoltaics (PV) because of its excellent light-harvesting capability, abundant elemental storage, and excellent stability. This study aimed to expand the application of Sb2(S,Se)3 solar cells with a substrate structure as a flexible or tandem device. The use of a hydrothermal method accompanied by a postselenization process for the deposition of Sb2(S,Se)3 film based on the solar cell substrate structure was first demonstrated. The mechanism of postselenization treatment on crystal growth promotion of the Sb2(S,Se)3 film and the defect passivation of the Sb2(S,Se)3 solar cell were revealed through different characterization methods. The crystallinity and the carrier transport property of the Sb2(S,Se)3 film improved, and both the interface defect density of the Sb2(S,Se)3/CdS interface and the bulk defect density of the Sb2(S,Se)3 absorber decreased. Through these above-mentioned processes, the transport and collection of electronics can be improved, and the defect recombination loss can be reduced. By using postselenization treatment to optimize the absorber layer, Sb2(S,Se)3 solar cells with the configuration SLG/Mo/Sb2(S,Se)3/CdS/ITO/Ag achieved an efficiency of 4.05%. This work can provide valuable information for the further development and improvement of Sb2(S,Se)3 solar cells.

MoSe2 nanosheets confined in N-doped carbon fibers as robust and capacitive anode of high performance Na-ion capacitors

Enhancing the rate and cycle performance of anode materials is the key in developing high performance Li/Na/K-ion capacitors. Molybdenum selenide (MoSe2) has been well studied as a potential high rate anode material for Na-ion capacitors based on its lamellar structure and large interlayer space. However, the MoSe2 anode usually suffers from inferior cycling stability especially when directly exposing to electrolyte. Herein, a composite anode material with MoSe2 nanosheets confined in N-doped carbon fibers is prepared by electrospinning and post-selenization process, which exhibits highly capacitive Na ion storage behavior and stable cycle performance in Na-metal half cells. When it is coupled with a pomelo peel-derived porous carbon cathode that is pre-mixed with sodium oxalate as the pre-sodiation additive, the assembled Na-ion capacitors display outstanding energy-power performance, including ultrahigh energy densities of 116 and 79 Wh kg−1 achieved at 197 and 8318 W kg−1, respectively, and a quite good stability in a long term cycle test. These results convincingly demonstrate that the composite with MoSe2 nanosheets confined in N-doped carbon fibers can be promising high capacitive and stable anode material for high performance Na-ion capacitors.

Efficiency improvement of electrodeposition-processed Cu(In,Ga)Se2 solar cell with widen surface bandgap by spin-coating In2S3 thin film

The Cu(In,Ga)Se2 (CIGSe) -based solar cell is a promising candidate in the photovoltaic market due to its excellent performance. It was reported that the surface bandgap of CIGSe is crucial to improve the device properties. However, in the post-selenization process of precursor layers, Ga tends to accumulate at the back contact leading to a narrow surface bandgap. In this work, the surface bandgap of CIGSe film was successfully widened by a spin-coating In2S3 thin film on the CIGSe surface. After annealing treatment of the CIGSe/In2S3 stack, sulfur incorporates into the absorber layer and a Cu-poor surface composition is formed. Thus, a surface inversion of CIGSe from p-type to n-type occurs leading to formation of a buried homojunction. The effect of different In2S3 thicknesses on device performance were investigated. A champion efficiency of 12.88 % for CIGSe solar cell was obtained with 40 nm In2S3 compared to 10.03 % for the reference device without In2S3. However, the performance of CIGSe solar cells were deteriorated with In2S3 film thicknesses over 40 nm. These results demonstrate that a suitable In2S3 film thickness is significant to increase the surface bandgap and promote the efficiency.

Influence mechanism of Cd ion soaking on performance of flexible CZTSSe thin film solar cells

Realizing flexible Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cell with high efficiency and excellent mechanical durability has always been a challenging task in green demanded era. In this work, Cu2CdxZn1-xSn(S,Se)4 (CCZTSSe) absorber was synthesized by selenizing Cd2+ treated CZTS precursor. Due to the powerful ability of Cd2+ soaking in boosting grain growth, the grain size of CCZTSSe was remarkably increased from nano to micron level. Cd atom actually act entering into the lattice and replaces Zn location in the post-selenization process. The band gap of CCZTSSe exhibits a decreasing trend (1.37 eV–1.29 eV) as x increases from 0 to 0.13. In comparison to CZTSSe absorber without Cd2+ soaking treatment, Cu2CdxZn1-xSn(S,Se)4 (x = 0.03, 0.07 and 0.13) can establish the heterojunction with better matching effect with CdS buffer layer, demonstrating an enhanced conduction band offset (CBO). The improved heterojunction characteristic substantially prevents carrier recombination caused by interface state defects, which can be the crucial reason of the enhanced device performance. Finally, for x = 0.07, the device efficiency was optimized to 4.38%. This systematic work offers a novel solution for vital problems encountered in flexible CZTSSe thin film solar cells, which can lead to prospective applications in wearable devices.

Aqueous spray pyrolysis of CuInSe2 thin films: Study of different indium salts in precursor solution on physical and electrical properties of sprayed thin films

Herein, we deposited CuInSe2(CISe) thin films by using aqueous spray deposition method and post selenization process. The effect of different indium precursor salts including indium chloride, indium nitrate and indium acetate on the structural, morphological, optical and electrical properties of sprayed CISe layers has been studied by using x-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM-EDS), optical transmission (UV–Vis), Mott-Schottky analysis, I–V dark measurements. Although all the deposited thin films show a chalcopyrite tetragonal ordering structure of CISe, the crystallinity, morphology, and electrical characteristics are strongly influenced by the type of indium salt. A highly compact film with large grains (500–1000 nm) can be obtained after selenization of deposited film from indium chloride precursor while indium nitrate precursor results in low grains size and indium acetate precursor leads to rough surfaces with very small grain size. According to Mott-Schottky results, all films are p-type with carrier concentration in the range of ~1017 cm−3 to ~1019 cm−3 and the smallest value of 2.8 × 1017 cm−3 is obtained for CISe film deposited from indium nitrate precursor. The XRD and J-V dark results revealed that the CISe films deposited from indium chloride precursor demonstrates better crystallinity and higher mobility relative to other precursors.

Overview of Ge-incorporated kesterite solar cells

<p indent=0mm>Kesterite (CZTS(e)) solar cell has attracted tremendous interest for its feature: Earth-abundant composition, convenient fabrication process, environmental friendliness and low cost. However, the severe large voltage deficient in CZTS(e) solar cell remains a challenge for further enhancement of the power conversion efficiency (PCE). In this prospect, three mechanisms are proposed: Cu/Zn disorder, potential interfacial losses and Sn-related deep-level defects. Sn-related deep-level defects are the most detrimental and hardest factor to manipulate due to the low energy of the formation of atomic antisite and multivalency nature of Sn. Adding extrinsic elements into the absorber layer is of an important method to passivate Sn-related defects. Among them, incorporation of Ge (CZTS:Ge) shows great potential. Comparing to Sn, Ge is more likely to be stabilized at +4 oxidation state. DFT calculation suggests that the deep-level defect density of <sc>CZTS(e):Ge</sc> is much smaller than that of CZTS(e). The maximum trap-limited conversion efficiency can be promoted to 24.1% with Ge incorporation compared with 20.9% in intrinsic CZTS(e). Early works show that CZTS(e):Ge solar cells present relative higher <italic>V</italic>_oc and has reached 12.3% power conversion efficiency (PCE), promising to champion the efficiency of CZTS(e) solar cell. Up to date, the benefits from Ge incorporation can be summarized in three aspects. First, Ge incorporation can induce the formation of Ge-Se low-temperature liquid phase as crystallization flux during annealing, which finally enlarges grain size and promote morphology. In the meantime, Sn-Se phases formation can be minimized through a modified reaction pathway brought by Ge doping. Second, Sn-related deep-level defects experimentally observed will be passivated when Ge is incorporated. Third, the energy difference between kesterite, stannite and primitive mixed CuAu is enlarged in Cu₂ZnGeS₄, indicating that Ge may stabilize kesterite in absorber and suppress band tailing caused by atomic disorder (or phase instability). To break through current efficiency bottleneck of CZTS(e) solar cells, we prospect the futural directions in constructing CZTS(e):Ge. First, Zn composition in absorber should be handled with great care to suppress the formation of Ge_Zn-Cu_Zn further. Next, modulation of the gradient band gap, achieved by vertical Ge-Sn compositional gradient in absorber, is also an important aspect. How to avoid the fast diffusion of Ge to form the vertical Ge-Sn gradient will be of the most essential question. Vertical control of independent Sn composition or Ge incorporation in the post-selenization process may be two potential solutions. Furthermore, the nature of the wide band gap of pure sulfide CZTS(e):Ge makes itself suitable to fabricate the top cell in tandem solar cell. Finally, interface modifications and band engineering in CZTS(e) solar cells will also benefit in constructing CZTS(e):Ge solar cells.

Pulsed rapid thermal process for tailoring the surface sulfurization of CIGSe thin film at low temperature

Surface sulfurization is an effective way for CIGSe thin film to implement front graded bandgap. The controllable high S content with shallow diffusion depth into the film is key for the sulfurization. However, the degree of the sulfurization is closely related to the reaction temperature, thus it is difficult to control the diffusion depth of S into the CIGSe thin film effectively with high S content in such shallow depth. In this study, a pulsed sulfurization process is employed to realize a surface sulfurization as well as a high S content in a shallow diffusion depth of S into CIGSe at low substrate temperature, which provides an important way to fabricate double graded bandgap films prepared by post-selenization process. Structural analysis confirms the feasibility of the pulsed rapid thermal processing sulfurization. The device with surface sulfurization has the EA of N1 defects shifted to shallow position from 54 meV to 143 meV down to about 26 meV and 110 meV, respectively. The Voc, FF, and Jsc are improved obviously. Finally, the efficiency of CIGSSe thin film solar cell, based on the electrodeposition and selenization, increases by 20% with the improvement of Voc and FF.

Design of suppressing optical and recombination losses in ultrathin CuInGaSe2 solar cells by Voronoi nanocavity arrays

Cu(In, Ga)Se 2 (CIGS) solar cells have reached efficiencies over 23%. However, the scarcity of In and Se makes reducing the thickness of CIGS thin-film absorber desirable for mass production with low-cost and time-saving processes. Meanwhile, CIGS solar cells based on different architectures and strategies have drawn much attention for significant performance over conventional technologies, but rational design guidelines for optical and electrical performance optimization are yet to be completed. In this work, the reduced thickness of the CIGS thin film with the optical and electrical loss-passivated molybdenum Voronoi nanocavity arrays (VNCAs) electrodes were demonstrated. A structural-model under conformally coating criteria was investigated and optimized by a finite-difference time-domain method. The reduced parasitic absorption and rear surface recombination by Al 2 O 3 passivation layers on VNCAs substrates give rise to enhanced V OC and J SC up to 9.5 and 8.5%, respectively. These results confirm that the novel VNCAs electrodes can provide a cost-effective way for ultrathin CIGS solar cells with high efficiency. Design of suppressing optical and recombination losses in ultrathin CuInGaSe 2 solar cells by voronoi nanocavity arrays was demonstrated. The reduced parasitic absorption and rear surface recombination by Al 2 O 3 passivation layers on VNCAs substrates give rise to enhanced V OC and J SC up to 9.5 and 8.5 %, respectively. • The passivation of electrical and optical losses was achieved by a glancing angle deposition system. • The criteria of conformal coating is applied in the detailed optical modeling. • The effect of rear surface passivation was studied before and after post-selenization process. • The Al 2 O 3 layer shows superior passivation effects in electrical and optical losses.

Effect of Cu content in CIGSe absorber on MoSe2 formation during post-selenization process

MoSe2 layers, which would help to form ohmic contact and improve the adhesion, were formed at the Mo/CIGSe interface during the CIGSe preparing process. However, a thick MoSe2 layer could introduce carrier recombination center, high contact resistance, and might result in poor adhesion of CIGSe films, which played a deleterious role in the efficiency of the devices. In this study, the effect of Cu content and Ga diffusion on the formation of MoSe2 layer was investigated. The thick MoSe2 layer tended to form with Cu/(In + Ga) < 0.7, and MoSe2 was difficult to form at the Mo/CIGSe interface when Cu/(In + Ga) > 0.9. Finally, CIGSe thin film with large grains and a thin MoSe2 layer was obtained with the value of Cu/(In + Ga) between 0.8 and 0.9, and an 11.04% efficiency CIGSe solar cell was fabricated with the open circuit voltage of 505 mV.

Performance and stability enhancement of Cu(InGa)Se2 solar cells on ultrathin glass by potassium incorporation

Flexible Cu(InGa)Se2 solar cells fabricated on metal foils and plastics have achieved high conversion efficiency so far. However, metal impurities and low temperature tolerance hinder them from further considerable development. Here, 150 μm-thick ultrathin glass with desirable advantages was applied as substrate for Cu(InGa)Se2 solar cell. Potassium element was doped by a simple method during the post-selenization process. The results showed that the KInSe2 phase existed in K-doped Cu(InGa)Se2 films. The K-doped CIGS films were more compact than the pristine one due to the fact that K incorporated in films could form quasi-liquid alkali-metal-Se compounds and improve the compactness of films. K-incorporated CIGS films exhibited enhanced p-type conductivity and different surface energy level. Consequently, K-doped Cu(InGa)Se2 solar cell achieved an optimal efficiency of 8.3%, which was relatively 43% higher than that of pristine solar cell. Investigation of performance and stability of solar cells manifested that the K incorporation retarded the performance degradation of device during cyclic bending.

One-step RF magnetron sputtering method for preparing Cu(In, Ga)Se2 solar cells

Cu(In, Ga)Se2 (CIGS) solar cell is one of the most promising thin film solar cells. However the marketization of the CIGS solar cells is hindered by the uncertainty of the element ratios. Traditional sputtering with post selenization is one of the most widespread methods to produce the CIGS solar cells. Nevertheless, the post selenization process is the most difficult part of this technique, which could lead to element mismatch and heterogeneous. To simplify the preparing process, Cu(In, Ga)Se2 (CIGS) solar cells were prepared without post-selenization process by RF sputtering CIGS target with abundant Se element. We focus on the effect of working pressure, substrate temperature and sputtering power on the properties of CIGS solar cells. When CIGS thin film was deposited at 580 °C, 0.8 Pa working pressure and 160 W sputtering power, the solar cell showed the highest power conversion efficiency (PCE) of 5.77%, which is only 0.64% lower than that of the solar cell prepared by traditional sputtering with post selenization method, and the two kinds of solar cells have same structure without MgF2 antireflection layer, but the one-step sputtering method could greatly simplify the manufacture process of the CIGS solar cells. Our work makes clear that element Se would run off almost half during the sputtering process. And the element atomic ratios and the photovoltaic properties could be controlled by changing the sputtering parameters.

Influence of Cu on Ga diffusion during post-selenizing the electrodeposited Cu/In/Ga metallic precursor process

Gallium accumulation, caused by faster reaction of indium with Se than gallium with Se, is a critical issue for post-selenization process, which limits the optimization of surface energy bandgap and open circuit voltage of CIGSe thin film solar cell. In this study, large-grained and compact CIGSe thin film was successful fabricated by electrodeposition and a three-step vapor Se/N2/vapor Se reaction process. The influence of the Cu content on gallium diffusion and grain growth of CIGSe thin film was studied. The compositions, element distributions, and morphologies of CIGSe thin films were studied. The results revealed that the gallium diffused homogenizely through the film with Cu/(In+Ga) < 0.9, while accumulated at the back contact region with Cu/(In+Ga) > 0.9. Single phase and large-grained CIGSe thin films were obtained with Cu/(In+Ga) ratios between 0.78 and 0.9. Cu(In,Ga)Se2 solar cells made with the CIGSe thin films presented highest efficiency of 11.22%. The solar cell based on the single phase and large-grained CIGSe absorber with Cu/(In+Ga) = 0.85 presents highest conversion efficiency of 11.22%, fill factor of 63.83% and VOC of 514 mV.

Optimization of Post-selenization Process of Co-sputtered CuIn and CuGa Precursor for 11.19% Efficiency Cu(In, Ga)Se2 Solar Cells

In this work, CuInGa alloy precursor films are fabricated by co-sputtering of CuIn and CuGa targets simultaneously. After selenization in a tube-type rapid thermal annealing system under a Se atmosphere, the Cu(In, Ga)Se2 (CIGS) absorber layers are obtained. Standard soda lime glass (SLG)/Mo/CIGS/CdS/i-ZnO/ITO/Ag grid structural solar cells are fabricated based on the selenized CIGS absorbers. The influences of selenization temperatures on the composition, crystallinity, and device performances are systematically investigated by x-ray energy dispersive spectroscopy, x-ray diffraction, Raman spectroscopy, and the current density–voltage (J–V) measurement. It is found that the elemental ratio of Cu/(In + Ga) strongly depends on the selenization temperatures. Because of the appropriate elemental ratio, a 9.92% conversion efficiency is reached for the CIGS absorber selenized at 560°C. After the additional optimization by pre-annealing treatment at 280°C before the selenization, a highest conversion efficiency of 11.19% with a open-circuit (Voc) of 456 mV, a short-circuit (Jsc) of 40.357 mA/cm2 and a fill factor of 60.82% without antireflection coating has been achieved. Above 13% efficiency improvement was achievable. Our experimental findings presented in this work demonstrate that the post-selenization of co-sputtered CuIn and CuGa precursor is a promising way to fabricate high quality CIGS absorbers.

Bandgap-Graded Cu2Zn(Sn1–xGex)S4 Thin-Film Solar Cells Derived from Metal Chalcogenide Complex Ligand Capped Nanocrystals

We demonstrate organic residue free, bandgap-graded Cu2Zn(Sn1–xGex)S4 (CZTGeS) thin-film solar cells based on metal chalcogenide complex (MCC) ligand capped nanocrystals (NCs). The bandgap of the CZTGeS films is tuned by varying the amount of Sn2S64– MCC ligand absorbed on the surface of the Cu2ZnGeS4 (CZGeS) NCs, without an undesirable postselenization process. Using CZGeS NCs inks with three different Sn/(Ge+Sn) ratios, bandgap-graded CZTGeS thin films are obtained via multicoating and annealing procedures. Compositional and spectroscopic analyses along the film thickness confirm that the band-graded CZTGeS absorber layer, with a gradually increasing bandgap from the back contact to the p–n junction, is successfully accomplished. Compared with an ungraded band structured CZTGeS cell, this normal grading structure facilitates both higher short circuit current and open-circuit voltage, facilitating a power conversion efficiency of 6.3%.

Structurally tailored Cu(InxGa1 − x) Se2 thin films via RF magnetron sputtering

Cu(InxGa1−x) Se2 (CIGS) thin films were deposited onto soda-lime glass substrates with Mo coating via the one step radio frequency (RF) magnetron sputtering without a post-selenization process at the substrate temperature varying from 550°C to 630°C. The effect of deposition temperature on the structural properties of CIGS thin films has been characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX). It was found that an increased deposition temperature of up to 580°C contributes to produce the smooth surface, large grain size, and increased crystallinity of the thin films. But further increased deposition temperature results in a decrease in smoothness and an increase in grain size. The optimized temperature (580°C) shows the best effect on the composition and formation of the chalcopyrite structure without impurities.