Nonvacuum Solution Synthesis of (Ag,Cu)(In,Ga)Se2 Absorbers for Applications in Thin‐Film Solar Cells

The effects of selenization temperatures on the phase formation and the photovoltaic properties of silver‐ion‐doped Cu(In,Ga)Se₂ (ACIGS) films were investigated. Cu_2?xSe phase coexisted with CuInSe₂ phase in the films as the selenization temperature was relatively low. Increasing the selenization temperatures promoted the formation of the chalcopyrite phase and increased the grain size. Upon increasing the selenization temperature to 600°C, single‐phased ACIGS films with a grain size of 2.1–2.2 μm were successfully synthesized. The incorporation of Ag⁺ and Ga³⁺ ions into CuInSe₂ during the phase formation of ACIGS elevated the band gaps of the films, thereby improving the open‐circuit voltage (V_oc) of the solar cells. The grain growth on raising the selenization temperatures also elevated the short‐circuit current (J_sc) values owing to the suppression of the electron‐hole recombination at grain boundaries. In the diode analysis, the facilitated phase formation suppressed the shunt path, decreasing the values of the diode factor (A), shunt conductance (G), and saturated current (J_o), thereby improving the cell performance. In this study, ACIGS solar cells with an efficiency of 7.21% prepared via the nonvacuum process were first demonstrated.     

Preparation and Characterization of Copper Gallium Diselenide Thin Films from the Solgel‐Derived Precursors

A simple process for preparing CuGaSe₂ (CGS) absorber layers was developed in this study. The solgel‐derived Cu‐Ga‐O precursor paste with variable Ga³⁺/Cu²⁺ ratios was coated on glass substrates using a doctor‐blade technique. The precursor films were selenided with a selenium vapor at the temperature ranging from 250 to 550°C. The GIXRD patterns showed that single‐phase CuGaSe₂ through the whole films was obtained at a Ga³⁺/Cu²⁺ molar ratio of 1.5 on selenization at 450°C. The Raman measurements also indicated that the grown CuGaSe₂ thin films exhibited the chalcopyrite structure. The SEM images of the films reveal that with an increase in Ga/Cu ratio in the films, the amount of Cu₂Se particles on the surface of the film was reduced. The resistivity of the films was increased with the increase in Ga content in the films. The formation mechanism of CuGaSe₂ thin films was proposed based on the XRD and Raman measurements of the films. The binary copper selenides are formed first, and then these phases lead to the formation of CuGaSe₂.     

Effects of ammonia concentration on the formation of CdS fabricated via microwave‐assisted chemical bath deposition

The microwave‐assisted chemical bath deposition (MACBD) process was successfully developed in this study for the preparation of cadmium sulfide (CdS) films as the buffer layers in Cu(In,Ga)Se₂ solar cells. The MACBD process reduces the reaction time to just 8 min. During the MACBD process, increasing the concentration of NH₄OH in the solution effectively reduced the thickness of the films as well as the particle sizes of in CdS films. At high NH₄OH concentrations, the heterogeneous nucleation of CdS dominated, and the formation of films was controlled via the ion‐by‐ion growth mechanism. Increasing the concentration of NH₄OH from 1 to 2.5 M significantly increased the conversion efficiency of the fabricated CIGS solar cells from 7.15% to 9.12%. The increase in the efficiency was attributed to an increase in the absorption of incident light and the enhancement of the carrier collection due to a reduction in the thickness of the prepared CdS films. According to diode analysis, the improvement in the diode ideality factor and leakage current was owing to the uniform coverage of CdS films and a reduction in series resistance associated with a decrease in the thickness of CdS films. When the concentration of ammonia was further increased to 3 M, incomplete coverage of CdS films on CIGS layers resulted in the formation of shunt paths and degraded the cell performance. This study demonstrated that CdS films prepared using the MACBD process with the optimum concentration of ammonia effectively improved the photovoltaic performance of Cu(In,Ga)Se₂ solar cells.     

CIGS absorbing layers prepared by RF magnetron sputtering from a single quaternary target

Cu(In_1−xGa_x)Se₂ (CIGS) thin films were prepared by RF magnetron sputtering from a single quaternary target at multiple processing parameters. The structural, compositional, and electrical properties of the as-deposited films were systematically investigated by XRD, Raman, SEM, and Hall effects analysis. The results demonstrate that by adjusting the processing parameters, the CIGS thin films with a preferential orientation along the (112) direction which exhibited single chalcopyrite phase were obtained. The films deposited at relatively higher substrate temperature, sputtering power, and Ar pressure exhibited favorable stoichiometric ratio (Cu/(In+Ga):0.8–0.9 and Ga/(In+Ga):0.25–0.36) with grain size of about 1–1.5 µm, and desirable electrical properties with p-type carrier concentration of 10¹⁶−10¹⁷ cm⁻³ and carrier mobility of 10–60 cm²/Vs. The CIGS layers are expected to fabricate high efficiency thin film solar cells.     

CZTSe solar cells prepared by electrodeposition of Cu/Sn/Zn stack layer followed by selenization at low Se pressure

Cu₂ZnSnSe₄ (CZTSe) thin films are prepared by the electrodeposition of stack copper/tin/zinc (Cu/Sn/Zn) precursors, followed by selenization with a tin source at a substrate temperature of 530°C. Three selenization processes were performed herein to study the effects of the source of tin on the quality of CZTSe thin films that are formed at low Se pressure. Much elemental Sn is lost from CZTSe thin films during selenization without a source of tin. The loss of Sn from CZTSe thin films in selenization was suppressed herein using a tin source at 400°C (A2) or 530°C (A3). A copper-poor and zinc-rich CZTSe absorber layer with Cu/Sn, Zn/Sn, Cu/(Zn + Sn), and Zn/(Cu + Zn + Sn) with metallic element ratios of 1.86, 1.24, 0.83, and 0.3, respectively, was obtained in a selenization with a tin source at 530°C. The crystallized CZTSe thin film exhibited an increasingly (112)-preferred orientation at higher tin selenide (SnSe _x ) partial pressure. The lack of any obvious Mo-Se phase-related diffraction peaks in the X-ray diffraction (XRD) diffraction patterns may have arisen from the low Se pressure in the selenization processes. The scanning electron microscope (SEM) images reveal a compact surface morphology and a moderate grain size. CZTSe solar cells with an efficiency of 4.81% were produced by the low-cost fabrication process that is elucidated herein.     

Electrodeposition of Ag and Pd on a reconstructed Au(1 1 1) electrode surface studied by in situ scanning tunneling microscopy

Electrochemical deposition of Ag and potential-induced structural change of the deposited Ag layer on a reconstructed surface of Au(1 1 1) electrode were followed by in situ scanning tunneling microscope (STM). A uniform Ag monolayer was formed on a reconstructed Au(1 1 1) surface in a 50-mM H₂SO₄ solution at +0.3 V (vs. Ag/AgCl) after adding a solution containing Ag₂SO₄ so that the concentration of Ag⁺ in the STM cell became ca. 2 μM. No characteristic height corrugation such as the Au reconstruction was observed on the surface, indicating that the lifting of the substrate Au reconstruction occurred by Ag deposition. The formed Ag monolayer was converted to a net-like shaped Ag nano-pattern of biatomic height when the potential was stepped from +0.3 to −0.2 V in the solution containing 2 μM Ag⁺. This result indicates that the substrate Au(1 1 1)-(1 × 1) surface was converted to the reconstructed surface even in the presence of Ag adlayer. Quite different structure was observed for Pd deposition on a reconstructed surface of Au(1 1 1) electrode at +0.3 V and the origin for this difference between Ag and Pd deposition is discussed.     

Solution-based synthesis of dense,large grained CuIn(S,Se)2 thin films using elemental precursor

Compared with the expensive and complicated vacuum techniques, the solution-based process to deposit I-III-VI₂ chalcogenide thin films (I=Cu, III=In or Ga, VI=S or Se) has attracted great interests due to its lower cost, higher scalable production and better application in flexible substrate. Herein, a low-toxic and high-active mixture solvent comprised of 1, 2-ethanedithiol and 1,2-ethylenediamine is utilized to dissolve elemental Cu, In and S powders at 60 °C, forming the CuInS₂ (CIS) precursor solution. After spin coating and annealing in a both Ar gas and selenium atmosphere, a dense and large-grained chalcopyrite CuIn(S,Se)₂ (CISSe) thin films with a close-packed grain size of ~800 nm are prepared, eliminating a undesired fine fine-grained bottom layer. In addition, the selenization temperature of the CISSe thin films is also discussed, which influences the phase composition, crystallinity and morphology of CISSe thin films. Photovoltaic device of the CISSe-based thin films is fabricated, obtaining a power conversion efficiency of 6.2% with an active cell area of 0.5 cm² under AM 1.5 illumination.     

Influences of Ga concentration on performances of CuInGaSe2 cells fabricated by sputtering-based method with ceramic quaternary target

Copper Indium Gallium Selenide (Cu(In,Ga)Se₂, CIGSe) absorbers with different Ga contents were prepared by sputtering CIGSe ceramic targets and post-annealing. CIGSe solar cell devices were fabricated with other functional layers. The device performances and absorber properties were investigated. Increasing Ga content led to an increase in V_OC and a decrease in J_SC. Ga was supposed to diffuse towards back contact during the annealing process. The best performance was obtained as the ratio of Ga/(In + Ga) reaches 0.32 with the efficiency of 13.8% and a V_OC of 537 mV.     

Reaction of Ozone with Ag(I)—Mechanistic Considerations

Ozone reacts slowly with Ag⁺ (circumneutral pH, k = (11 ± 3) × 10^?2 M^?1 s^?1). After some time, ozone decay kinetics may suddenly become faster with the concomitant formation of silver sol. As primary process, an O-transfer from O₃ to Ag(I) is suggested, whereby Ag(III) is formed [Ag⁺ + O₃ + 2 H₂O → Ag(OH)₃ + O₂ + H⁺]. This conproportionates with Ag(I), which is in large excess, leading to Ag(II) [Ag⁺ + Ag(OH)₃ ? 2 Ag(OH)⁺ + HO^?]. Further, Ag(II) reacts with ozone in a high exergonic reaction [Ag(OH)⁺ + O₃ → Ag + 2 O₂ + H⁺], where ozone acts as a reducing agent. Thereby, a single silver atom, Ag, is formed that can be oxidized by O₂ and O₃ or can aggregate to a silver sol. Aggregation slows down the rate of oxidation. When Ag⁺ is complexed by acetate ions, ozone decay and silver sol formation are speeded up by enhancing Ag(II) formation [Ag(I)acetate + O₃ → Ag(III)acetate → Ag(II) + CO₂ + ?CH₃]. In the presence of oxalate, the formed complex reacts faster with ozone than Ag⁺, and Ag(III)oxalate decarboxylates rapidly [Ag(I)oxalate + O₃ → Ag(III)oxalate → Ag⁺ + 2 CO₂]. This enhances ozone decay but prevents silver sol formation. Quantum chemical calculations have been carried out for substantiating mechanistic suggestions.     

Selenization treatment on Ag8SnSxSe6-x counter electrode of dye-sensitized solar cells in improving its electron transfer and electrocatalytic activity

In this paper, Ag₈SnS₆ powder was synthesized by the one-pot method, then prepared into Ag₈SnS₆ and Selenization treated Ag₈SnS_xSe_6-x thin films. The effects brought by the amounts of added Se powder during the annealing process on the product phases, structures, and morphologies are characterized, and the electrochemical property and the cell efficiency as assembled into the counter electrode (CEs) for dye-sensitized solar cells (DSSCs) were investigated. It showed Se into the Ag₈SnS₆ lattice occupied the site of S to transform into Ag₈SnS_xSe_6-x. And the thin film also became unflatten since the particles became larger after Se doping. The cell efficiency of Ag₈SnS_xSe_6-x CEs reached 4.26%, which was increased by 28.31% compared to that of Ag₈SnS₆ CEs. Ag₈SnS_xSe_6-x CEs performed lower charge transfer resistance (Rct) and (△EPP), and an increased△E value between the conduction band level of CEs and the redox potential of electrolyte. After 10 cycles, the almost unchanged cathode/anode current density implied the Ag₈SnS_xSe_6-x CEs received good structure stability. Selenization treatment was able to facilitate electron transport and enhance the electrocatalytic activity, and as expected to be a promising method in improving the performance of the DSSCs.     

Ultra‐low temperature sintering microwave dielectric ceramics based on Ag2O–MoO3 binary system

The Ag₂Mo₂O₇ and Ag₆Mo₁₀O₃₃ ceramics for ultra‐low temperature co‐fired ceramic application were prepared by the solid‐state reaction route. The optimized densification temperatures of Ag₂Mo₂O₇ and Ag₆Mo₁₀O₃₃ are 460°C and 500°C, respectively. The phase structures and microstructures of these ceramics were systematically studied. The Ag₂Mo₂O₇ ceramic sintered at 460°C/4 h exhibits excellent microwave dielectric properties with ε_r=13.3, Q×f=25 300 GHz and τ_f=?142 ppm/°C at 9.25 GHz. The Ag₆Mo₁₀O₃₃ ceramic sintered at 500°C/4 h shows the microwave dielectric properties with ε_r=14.0, Q×f=8500 GHz and τ_f=?50 ppm/°C at 9.00 GHz. Moreover, when Ag₂Mo₂O₇ samples are sintered at ultra‐low sintering temperatures of 420°C‐490°C, the Q×f values of them are all above 20 000 GHz. Besides, the Ag₂Mo₂O₇ ceramic does not react with silver powder or aluminum powder. The variation of relative permittivity, resonant frequency, and Q×f values as a function of operating temperature has been also studied. All the results indicate that the Ag₂Mo₂O₇ ceramic is a good candidate for ultra‐low temperature co‐fired microwave devices.     

CuInSe2 Formation from CuSe/In2Se3 and Cu2Se/In2Se3 Powders: Reaction Kinetics and Mechanisms

CuInSe₂ (CIS) powders were synthesized using CuSe, Cu₂Se, and In₂Se₃ as the raw materials. The formation mechanisms and reaction kinetics from CuSe/In₂Se₃ and Cu₂Se/In₂Se₃ powders in a selenium atmosphere were investigated. It was observed that the formation temperature of α‐CIS powders synthesized using Cu₂Se/In₂Se₃ as the raw materials was higher than that using CuSe/In₂Se₃. Both reactions for Cu₂Se/In₂Se₃ and CuSe/In₂Se₃ mixtures follow one‐dimensional diffusion‐controlled reactions with apparent activation energies of 124.3 and 73.2 kJ/mol, respectively. For both mixtures the indium‐rich β‐CIS phase resulting from Cu⁺ ion diffusion toward the In₂Se₃ phase was observed. The particle size and morphology of the newly formed CIS was similar to In₂Se₃, which indicated that the CIS formation kinetics may be dominated by the diffusion of Cu⁺ ions. The Cu–Se liquid phase resulting from the peritectic decomposition of CuSe₂ and CuSe at a relatively low temperature may promote Cu⁺ diffusion into the In₂Se₃ surface, assisting CIS formation.     

Laser Desorption Ionization Time‐of‐Flight Mass Spectrometry of Glasses and Amorphous Films from Ge–As–Se System

Laser Desorption Ionization Time‐of‐Flight Mass Spectrometry was exploited for the characterization of Ge–As–Se chalcogenide glasses and corresponding thin films fabricated using pulsed laser deposition. Main achievement of the paper is the determination of laser generated clusters’ stoichiometry. The clusters observed were As_b⁺ (b = 1–3), Se₂^?, binary As_bSe⁺ (b = 1–3), As_bSe_c^? (b = 1–3, c = 1–4), Ge₂Se_c^? (c = 2–3), As₃Se₂⁺, Ge₂As_b^? (b = 2–3), Ge₃As_b^? (b = 1–2), Ge₃Se₄^?, As₅Se_c^? (c = 4–5), GeAsSe₄^?, Ge_aAsSe₅^? (a = 1–4), GeAs₂Se₃^?, GeAs₃Se₂^?, Ge₂As₂Se₂^?, Ge₂AsSe_c^? (c = 6–7), and GeAs₃Se_c^? (c = 5–6) (in positive as well as in negative ion mode). The stoichiometries of identified species are compared with the structural units of the glasses/thin films revealed via Raman scattering spectra analysis. Some species are suggested to be fragments of bulk glass as well as thin films. Described method is useful also for the evaluation of the contamination of chalcogenide glasses or their thin films.     

Mineralizer effect on the synthesis of two types of one-dimensional chains silver-selenogermanate and selenostannate

Two type of one-dimensional compounds, K₂Ag₂GeSe₄(2) and K₃AgSn₃Se₈(4), were synthesized with thiophenol as a mineralizer, whilst two oligomers, Cs₄Ge₂Se₆ (1) and K₄Sn₃Se₈(3), were obtained in absence of thiophenol. Compounds 1 and 3 contain dimeric [Ge₂Se₆]^4? and trimeric [Sn₃Se₈]^4? anions, respectively. Compound 2 contains isolated GeSe₄ tetrahedra connected by linear-coordinated Ag⁺ ions to form an infinite anionic chains [Ag₂GeSe₄]^2?. The building blocks [Sn₃Se₈]^4? are linked by tetrahedral coordinated Ag⁺ ions to generate infinite chain [AgSn₃Se₈]^3? of 4.     

Investigation of bulk hybrid heterojunction solar cells based on Cu(In,Ga)Se2 nanocrystals

This work presents the systematic studies of bulk hybrid heterojunction solar cells based on Cu(In, Ga)Se₂ (CIGS) nanocrystals (NCs) embedded in poly(3-hexylthiophene) matrix. The CIGS NCs of approximately 17 nm in diameter were homogeneously blended with P3HT layer to form an active layer of a photovoltaic device. The blend ratios of CIGS NCs to P3HT, solvent effects on thin film morphologies, interface between P3HT/CIGS NCs and post-production annealing of devices were investigated, and the best performance of photovoltaic devices was measured under AM 1.5 simulated solar illumination (100 mW/cm²).     

Germanium-antimony-selenium-tellurium thin films: Clusters formation by laser ablation and comparison with clusters from mixtures of elements

Quaternary germanium-antimony-selenium-tellurium (Ge-Sb-Se-Te) thin films deposited from Ge_19.4Sb_16.7Se_63.9−xTe_x (x = 5, 10, 15, and 20) glass-ceramics targets by radio frequency magnetron sputtering were studied using laser ablation quadrupole ion trap time of flight mass spectrometry. Binary, ternary, and quaternary Ge_aSb_bSe_cTe_d clusters were formed and their stoichiometry was determined. By comparison of the clusters obtained from quaternary Ge-Sb-Se-Te thin films and those from ternary Ge-Sb-Te materials, we found that Ge-Te species are not detected from the quaternary system. Furthermore, Ge-Se and Se-Te species are missing in mass spectra generated from Ge-Sb-Se-Te thin films. From the Ge-Sb-Se-Te thin films, 16 clusters were detected while ternary Ge-Sb-Se glasses yielded 26 species. This might be considered as a signal of higher stability of Ge-Sb-Se-Te thin films which is increasing with a higher content of Te. The missing (Se₂⁺, Ge_aSb⁺ (a = 1–4), and GeSe_c⁺ (c = 1, 2)) and new (Ge⁺ and Sb_bTe⁺ (b = 1–3)) clusters may indicate that some of the structural features of the films (Ge₂Se_6/2 and Se₂Sb-SbSe₂) were replaced by (GeSe_4−xTe_x and SbSe_3−xTe_x) ones. In addition, when comparing the stoichiometry of clusters formed from Ge-Sb-Se-Te thin films with those from the mixtures of the elements, only Sb₃⁺ and SbSe⁺ were observed in both cases. The knowledge gained concerning clusters stoichiometry contributes to the elucidation of the processes proceeding during plasma formation used for the chalcogenide thin films deposition.     

Microstructures and photovoltaic performances of bismuth-ion doped Cu(In,Ga)Se2 films prepared via sputtering process

Bismuth-ion doped Cu(In,Ga)Se₂ (CIGS) solar cells were fabricated via sputtering technique. The influence of bismuth-ion doping on structural and photovoltaic characteristics of the fabricated CIGS films were explored in details. With doping of bismuth ions, the grain sizes of CIGS layers were enhanced appreciably due to liquid-phase sintering with the yielded intermediate compound. The secondary ion mass spectroscopy profile results indicated that the diffusion of bismuth ions into CIGS layers promoted dissemination of gallium species from the back contacts to the surface of CIGS layers. According to Hall measurement analysis, the carrier concentration in CIGS films was enhanced significantly with the doping of bismuth ions in the prepared films. The conversion efficiency of the bismuth-ion doped samples was increased approximately 10% in comparison with undoped samples due to the elevated gallium-ion diffusion and grain growth. Various photovoltaic parameters including saturated current and diode factors of the prepared doped CIGS solar cells were decreased owing to the inhibition of electron-hole recombination. This investigation demonstrated the improved photovoltaic performance and the structural characteristics of fabricated CIGS films after the doping of bismuth ions.     

N‐alkylation of chitosan by β‐halopropionic acids in the presence of various acceptors

N‐carboxyethylation of chitosan by β‐halopropionic acids in the presence of various proton and halogen ion acceptors was investigated. It has been observed that carboxyethylation of chitosan in aqueous medium is accompanied by the by‐processes of hydrolysis and dehydrohalogenation of the β‐halopropionic acids yielding β‐hydroxypropionic acid, bis(2‐carboxyethyl) ether, and acrylic acid. Degree of carboxyethyl substitution (DS) of chitosan and the relative rates of the by‐processes varied significantly depending on the conditions used and nature of the proton or halogen ion acceptor. At carboxyethylation of chitosan with the alkaline β‐bromopropionates, the DS increased in the order Cs⁺ < Rb⁺ < K⁺ ～ Na⁺ < Li⁺. For alkaline earth salts BrCH₂CH₂COOM_0.5 (M = Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), the highest DS was obtained with strontium and barium salts, which could be subsequently removed from the reaction mixture by precipitation as sulfates. Among the organic bases applied (tetrabutylammonium hydroxide, triethylamine, trimethylamine, pyridine, 4‐N,N‐dimethylaminopyridine, 2,6‐lutidine, and 1,5‐diazabicyclo[4.3.0] non‐5‐ene), the highest DS was obtained using a moderately strong base triethylamine. For the halogen acceptors (Pb²⁺, Ag⁺, Tl⁺), the stoichiometrically highest DS was achieved in a system comprising iodopropionic acid plus Tl⁺ and a comparable conversion rate was obtained using also a combination of chloropropionic acid and Ag⁺. A novel alternative preparative approach—gel‐state synthesis—was suggested that provides for the highest DS at the optimum reaction conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nuclear γ-resonance spectra and local surrounding of 121Sb and 129I atoms in CuI-PbI2-As2Se3 and CuI-SbI3-PbI2-As2Se3 films

The local surrounding of copper, antimony, and iodine atoms in multicomponent chalcogenide films CuI-PbI₂-As₂Se₃ and CuI-SbI₃-PbI₂-As₂Se₃ deposited from solutions of chalcogenide glass in n-butylamine has been studied by the Mössbauer spectroscopy method on ¹²¹Sb and ¹²⁹I isotopes. It was established that antimony atoms are in the Sb (III) state, where each antimony atom is surrounded by three selenium atoms. Copper atoms are in the Cu (I) state and are surrounded by iodine atoms. The local surrounding of copper, antimony, and iodine atoms in chemically deposited chalcogenide films is analogous to the local surrounding of atoms in the initial chalcogenide glass.