Preparation and Characterization of Silver‐Doped Cu(In,Ga)Se2 Films via Nonvacuum Solution Process

Cu(In,Ga)Se₂ films doped with different contents of silver ions (Ag⁺) were successfully prepared using nonvacuum spin coating followed by selenization at elevated temperatures. Increasing the Ag⁺ ion content increased the lattice parameters of the chalcopyrite structure, and shifted the A1 mode in the Raman signals to low frequencies. The band gaps of the prepared (Ag,Cu)(In,Ga)Se₂ (ACIGS) films were considerably increased, thereby increasing the open‐circuit voltage (V_oc) of the solar cells. As Ag⁺ ion content increased, the microstructures of ACIGS films became densified because the formed (Cu,Ag)₂In alloy phase with a low melting point facilitated liquid‐phase sintering. The evaporation of selenium species was correspondingly suppressed in the films during selenization, thereby reducing the selenium vacancies. The improvement in the microstructures and the defects of ACIGS films increased short‐circuit current (J_sc) and fill factor of the solar cells. The spectral response of the solar cells was also enhanced remarkably. This study demonstrated that incorporation of Ag⁺ ions into Cu(In,Ga)Se₂ films substantially improved the efficiency of the solar cells.     

A Promising Modified SILAR Sequence for the Synthesis of Photoelectrochemically Active Cu2ZnSnS4 (CZTS) Thin Films

A promising modified SILAR sequence approach has been employed for the synthesis of photoelectrochemically active Cu₂ZnSnS₄ (CZTS) thin films. To study the influence of sulfurization temperatures on the CZTS thin films, the CZTS precursor thin films were annealed at temperatures of 520, 540, 560, and 580 °C for 1 h in an H₂S (5 %)+Ar (95 %) atmosphere. These films were characterized for their structural, morphological, and optical properties using X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, and UV-vis spectrophotometer techniques. The film sulfurized at an optimized temperature of 580 °C shows the formation of a prominent CZTS phase with a dense microstructure and optical band gap energy of 1.38 eV. The photoelectrochemical (PEC) device fabricated using optimized CZTS thin films sulfurized at 580 °C exhibits an open circuit voltage (V_oc) of 0.38 V and a short circuit current density (J_sc) of 6.49 mA cm⁻², with a power conversion efficiency (η) of 0.96 %.     

Solvothermal Synthesis and Characterization of Chalcopyrite CuInSe2 Nanoparticles

The ternary I-III-VI₂ semiconductor of CuInSe₂ nanoparticles with controllable size was synthesized via a simple solvothermal method by the reaction of elemental selenium powder and CuCl as well as InCl₃ directly in the presence of anhydrous ethylenediamine as solvent. X-ray diffraction patterns and scanning electron microscopy characterization confirmed that CuInSe₂ nanoparticles with high purity were obtained at different temperatures by varying solvothermal time, and the optimal temperature for preparing CuInSe₂ nanoparticles was found to be between 180 and 220 °C. Indium selenide was detected as the intermediate state at the initial stage during the formation of pure ternary compound, and the formation of copper-related binary phase was completely deterred in that the more stable complex [Cu(C₂H₈N₂)₂]⁺ was produced by the strong N-chelation of ethylenediamine with Cu⁺. These CuInSe₂ nanoparticles possess a band gap of 1.05 eV calculated from UV–vis spectrum, and maybe can be applicable to the solar cell devices.     

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.     

Pyrrole‐based narrow‐band‐gap copolymers for red light‐emitting diodes and bulk heterojunction photovoltaic cells

A series of narrow‐band‐gap conjugated copolymers (PFO‐DPT) derived from pyrrole, benzothiadiazole, and 9,9‐dioctylfluorene (DOF) is prepared by the palladium‐catalyzed Suzuki coupling reaction with the molar feed ratio of 4,7‐bis(N‐methylpyrrol‐2‐yl)‐2,1,3‐benzothiadiazole (DPT) around 1, 5, 15, 30, and 50%. The obtained polymers are readily soluble in common organic solvents. The solutions and the thin solid films of the copolymers absorb light from 300 nm to 600 nm with two absorbance peaks at around 380 nm and 505 nm. The PL emission consists mainly of DPT unit emission at around 624–686 nm depending on the DPT content in solid film. The EL emission peaks are red‐shifted from 630 nm for PFO‐DPT1 to 660 nm for PFO‐DPT50. Bulk heterojunction photovoltaic cells fabricated from composite films of copolymer and [6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM) as electron donor and electron acceptor, respectively, in device configuration: ITO/PEDOT : PSS/PFO‐DPT : PCBM/Ba/Al shows power conversion efficiencies 0.15% with open‐circuit voltage (V_oc) of 0.60 V and short‐circuit current density (J_sc) of 0.73 mA/cm² under AM1.5 solar simulator (100 mW/cm²). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

New low bandgap conjugated polymer derived from 2, 7‐carbazole and 5, 6‐bis(octyloxy)‐4, 7‐di(thiophen‐2‐yl) benzothiadiazole: Synthesis and photovoltaic properties

To develop conjugated polymers with low bandgap, deep HOMO level, and good solubility, a new conjugated alternating copolymer PC‐DODTBT based on N‐9′‐heptadecanyl‐2,7‐carbazole and 5, 6‐bis(octyloxy)‐4,7‐di(thiophen‐2‐yl)benzothiadiazole was synthesized by Suzuki cross‐coupling polymerization reaction. The polymer reveals excellent solubility and thermal stability with the decomposition temperature (5% weight loss) of 327°C. The HOMO level of PC‐DODTBT is ‐5.11 eV, indicating that the polymer has relatively deep HOMO level. The hole mobility of PC‐DODTBT as deduced from SCLC method was found to be 2.03 × 10^?4 cm²/Versus Polymer solar cells (PSCs) based on the blends of PC‐DODTBT and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) with a weight ratio of 1:2.5 were fabricated. Under AM 1.5 (AM, air mass), 100 mW/cm^?2 illumination, the devices were found to exhibit an open‐circuit voltage (V_oc) of 0.73 V, short‐circuit current density (J_sc) of 5.63 mA/cm^?2, and a power conversion efficiency (PCE) of 1.44%. This photovoltaic performance indicates that the copolymer is promising for polymer solar cells applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and solar cells applications of EO‐PF‐DTBT polymer

Poly{[2,7‐(9,9‐bis‐(1‐(2‐(2‐methoxyethoxy)ethoxy)ethyl)‐fluorene)]‐alt‐[5,5‐(4,7‐di‐2′‐thienyl‐2,1,3‐benzothiadiazole)]} (EO‐PF‐DTBT) was synthesized by Suzuki coupling reaction. The polymer is soluble in common organic solvent, such as toluene, THF, and chloroform, and it also shows solubility in polar solvent, such as cyclopentanone. Solar cells based on EO‐PF‐DTBT and PC₆₁BM show maximum power conversion efficiency of 2.65% with an open circuit voltage (V_OC) of 0.86 V, a short circuit current density (J_SC) of 6.10 mA/cm², and a fill factor of 51% under AM 1.5G illumination at 100 mW/cm², which is the best results for fluorene and 4,7‐di‐2‐thienyl‐2,1,3‐benzothiadiazole copolymers and PC₆₁BM blend. The 1,8‐diiodooctane can work well to reduce the over‐aggregated phase structure in polymer solar cells. Our results suggest that the introducing high hydrophilic side chain into conjugated polymer donor materials can tune the aggregation structure and improve the solar cells performances. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40478.     

Liquid‐liquid phase split in ionic liquid + toluene mixtures induced by CO2

High pressure carbon dioxide was dissolved in ionic liquid + toluene mixtures to obtain the conditions of pressure and composition where a liquid‐liquid phase split occurs at constant temperature. Ionic liquids (ILs) with four different cations paired with the bis(trifluoromethylsulfonyl)imide ([Tf₂N]^?) anion were selected: 1‐hexyl‐3‐methylimidazolium ([hmim]⁺), 1‐hexyl‐3‐methylpyridinium ([hmpy]⁺), triethyloctylphosphonium ([P₂₂₂₈]⁺), and tetradecyltrihexylphosphonium ([P₆₆₆₁₄]⁺). The solubility of CO₂ was measured in the liquid mixtures at temperatures between 298 and 333 K and at pressures up to 8 MPa, or until the second liquid phase appeared, for initial liquid phase compositions of 0.30, 0.50, and 0.70 mole fraction of IL. Ternary isotherms were compared with the binary solubility of CO₂ in each IL and pure toluene. The lowest pressure for separating toluene in a second liquid phase was achieved by decreasing the temperature of the system, increasing the amount of toluene in the initial liquid mixture and using [hmim][Tf₂N]. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2968–2976, 2015     

Surface modifications of CIGS absorbers and their effects on performances of CIGS solar cells

The surface roughness of CIGS absorber and residual Cu–Se phase on the surface are two major factors greatly affecting the performance of CuInGaSe₂ (CIGS) solar cells with the absorbers fabricated by the selenization annealing of Cu–In-Ga precursors. In this work, Br₂–CH₃OH solution is used to etch the surfaces of CIGS films to address these two challenges. The effects of the etching treatment on CIGS films and devices are investigated. It is found that etching significantly reduces the film roughness and removes the Cu–Se phase. Thus, the performance of the device is improved within a certain range. In addition, it is found that CIGS films with suitable surface roughness effectively absorb incident light and possess a higher J_sc. However, excessive etching causes the film to be too thin, and the carrier recombination at the back electrode increases. Based on these characteristics, this work optimizes the Br₂ etching process.     

Ferroelectric nanodot formation from spin‐coated poly(vinylidene fluoride‐co‐trifluoroethylene) films and their application to organic solar cells

We demonstrated a facile route to the preparation of self‐assembled poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)] nanodots from spin‐coated thin films. We found that the initial film thickness would play an important role in the formation of such P(VDF‐TrFE) nanodots. Interestingly, the electric dipoles of such nanodots were self‐aligned toward the bottom electrode and their ferroelectric properties were determined by using piezoresponse force microscopy. In addition, the self‐polarized ferroelectric nanostructures were introduced to small molecular organic photovoltaic devices and allowed for enhancing the short circuit current density (J_sc) from 9.4 mA/cm² to 10.2 mA/cm² and the power conversion efficiency from 2.37% to 2.65%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41230.     

Effect of the grain size of nanoparticle dye‐coated titanium dioxide on the short‐circuit current density and open‐circuit voltage of an indium tin oxide/titanium dioxide/poly(acrylonitrile)–propylene carbonate–lithium perchlorate/graphite solar cell

A dye‐sensitized indium tin oxide (ITO)/titanium dioxide (TiO₂)/polyacrylonitrile (PAN)–propylene carbonate (PC)–lithium perchlorate (LiClO₄)/graphite solar cell was fabricated, and its performance was tested in the dark and under the illumination of a 100 mW/cm² light. Three TiO₂ samples were used in the device, namely, uncoated TiO₂, a TiO₂ film coated with methyl red dye, and a TiO₂ film coated with coumarin dye. The films were deposited onto an ITO‐covered glass substrate by a controlled hydrolysis technique assisted with a spin‐coating technique. The films were characterized by scanning electron microscopy to determine their average grain size. The smallest grain size (48 nm) was obtained for the uncoated film. An electrolyte of PAN–LiClO₄ with PC plasticizer was prepared by a solution‐casting technique. A graphite electrode was prepared on a glass slide by an electron‐beam evaporation technique. The device showed rectification properties in the dark and showed a photovoltaic effect under illumination. The device with the uncoated TiO₂ film showed the highest short‐circuit current density (2.0 μA/cm²) and an open‐circuit voltage of 0.64 V because it possessed the smallest grain size. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Butterfly nanostructures via regioregularly grafted multi‐walled carbon nanotubes and poly(3‐hexylthiophene) to improve photovoltaic characteristics

Butterfly nanostructures were designed using multi‐walled carbon nanotubes (CNTs) grafted with regioregular poly(3‐hexylthiophene) (RR‐P3HT) chains (CNT‐graft‐P3HT). The secondary crystallization of RR‐P3HT free chains onto CNT‐graft‐P3HT reflected the donor–acceptor supramolecules with a butterfly configuration, in which the CNT acted as the body of the butterfly and seeded crystallization of P3HT free chains resulted in the wings having a width of 37–38 nm. Butterfly supramolecules demonstrated high melting point (241.2 °C), fusion enthalpy (31.5 J g^?1) and crystallinity (85.13%). High photoluminescence quenching and thus donating–accepting property were also detected for the butterfly nanohybrids with a bandgap energy of 1.94 eV. Incorporation of butterfly nanostructures in the active layer of photovoltaic devices (P3HT:butterfly) conspicuously affected the system characteristics including short circuit current density (J_sc; 10.84 mA cm^?2), fill factor (FF; 56%) and power conversion efficiency (PCE; 3.94%). The inclusion of phenyl‐C71‐butyric acid methyl ester molecules as second acceptor in thin‐film active layers further increased the efficacy of systems, i.e. J_sc of 12.23 mA cm^?2, FF of 63%, open circuit voltage of 0.66 V and PCE of 5.08%, without considering external treatments and additives. © 2018 Society of Chemical Industry     

Synthesis and photovoltaic properties of two side‐chain polymeric metal complexes containing 8‐hydroxyquinoline and fluorene units with Zn(II) and Cd(II)

Two novel side‐chain polymeric metal complexes (PF1 and PF2) containing 8‐hydroxyquinoline and fluorene units with Zn(II) and Cd(II) having donor‐acceptor π‐conjugated structure have been synthesized and characterized using Fourier transform infrared, ¹H NMR, UV‐visible and photoluminescence spectroscopies, thermogravimetric analysis, differential scanning calorimetry, elemental analysis and cyclic voltammetry. Dye‐sensitized solar cells (DSSCs) based on PF1 and PF2 as the dye sensitizers exhibit good device performance with solar‐to‐electricity conversion efficiency up to 0.32% (J_sc = 0.83 mA cm^?2, V_oc = 0.62 mV and FF = 0.62) and 0.24% (J_sc = 0.69 mA cm^?2, V_oc = 0.59 mV and FF = 0.60), respectively, under simulated AM 1.5 G solar irradiation (100 mW cm^?2). The data show that these novel polymeric metal complexes are suitable for DSSCs. Copyright © 2012 Society of Chemical Industry     

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.     

Synthesis of two D‐π‐A polymers π‐bridged by different blocks and investigation of their photovoltaic property

The synthesis, characterization, photophysical and photovoltaic properties of two 5,6‐bis(octyloxy)benzo[c][1,2,5]thiadiazole‐containing wide‐band‐gap donor and acceptor D‐π‐A alternating conjugated polymers (HSD‐a and HSD‐b) have been reported. These two polymers absorb in the range of 300–700 nm with a band gap of about 1.88 and 1.97 eV. The HOMO energy levels were ?5.44 eV for HSD‐a and ?5.63 eV for HSD‐b. Polymer solar cells with HSD‐b :PC₇₁BM as the active layer demonstrated a power conversion efficiency (PCE) of 2.59% with a high V_oc of 0.93 V, a J_sc of 7.3 mA/cm², and a comparable fill factor (FF) of 0.38 under simulated solar illumination of AM 1.5G (100 mW/cm²) without annealing. In addition, HSD‐a :PC₇₁BM blend‐based solar cells exhibit a PCE of 2.15% with a comparable V_oc of 0.64 V, J_sc of 8.75 mA/cm^?2, and FF of 0.40. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41587.     

Preparation and Characterization of CIGSe Solar Cells by Ink Printing on Alumina Substrates with Self‐Synthesized Selenide Powders via an Environment‐Friendly and Cost‐Effective Dry Synthesis Route

CIGSe solar cells with an ink‐printing absorber layer were prepared on Mo‐coated alumina substrates. The use of alumina substrates can extend the process window to higher temperatures. The inks contained single‐phase CIGSe powder, which was formed by firing different selenide powders of Cu₂Se, In₂Se₃, and Ga₂Se₃ at 800°C. All these powders were synthesized with an environment‐friendly and cost‐effective powder process. The printed inks were sintered at 600–800°C. The solar cells had power conversion efficiency of 0.50%, an open‐circuit voltage of 27 mV, a short‐circuit current density of 37 mA/cm², and a fill factor of 0.50.     

Fast preparation of (111)‐oriented β‐SiC films without carbon formation by laser chemical vapor deposition from hexamethyldisilane without H2

(111)‐oriented β‐SiC films were prepared by laser chemical vapor deposition using a diode laser (wavelength: 808 nm) from a single liquid precursor of hexamethyldisilane (Si(CH₃)₃–Si(CH₃)₃, HMDS) without H₂. The effects of laser power (P_L), total pressure (P_tot) and deposition temperature (T_dep) on the microstructure, carbon formation and deposition rate (R_dep) were investigated. β‐SiC films with carbon formation and graphite films were prepared at P_L ≥ 170 W and P_to ≥ 1000 Pa, respectively. Carbon formation strongly inhibited the film growth. β‐SiC films without carbon formation were obtained at P_tot = 400‐800 Pa and P_L = 130‐170 W. The maximum R_dep was about 50 μm·h^?1 at P_L = 170 W, P_tot = 600 Pa and T_dep = 1510 K. The investigation of growth mechanism shows that the photolytic of laser played an important role during the depositions.     

Synthesis and properties of novel polyvinyl alcohol–lactic acid gels

This article describes a process for esterifying polyvinyl alcohol (PVA) with L‐lactide (LLA) and D,L‐lactic acid (LA), using ethyl acetate and N,N′‐dimethyl formamide at temperatures varying from 120 to 150°C. The grafting process was carried out under nitrogen to avoid possible oxidation or other degradation of the process ingredients and product. Lower T_g values were obtained for the PVA/LLA graft copolymers of higher LLA content suggesting some compatibility in the amorphous phase. Higher T_g values were observed for PVA/LA graft copolymers that yielded tough polymer films. The structure of the copolymers was studied by solid‐state ¹³C‐NMR, infrared spectroscopy, and differential scanning calorimetry (DSC). The PVA/LA films exhibited melt processability and good mechanical properties such as yield strength, tensile energy at break, modulus, and elongation at break. The polymer films produced through compression molding at 100°C showed good swelling properties. The transport coefficient (n) values determined from the plot of log(M_t/M_∞) vs. log t indicate Fickian behavior, and they are consistent with the reported literature values for other PVA systems. The nature of water in gels [bound water (W_b), freezing (W_f), and freezing bound (W_fb), and water content (W_t)] was evaluated from DSC data. The results demonstrate that PVA/LA hydrogels with good combination of thermal, physicomechanical, and swelling properties can be prepared via the lactic acid esterification of PVA polymer process described. Besides being melt processable, the PVA/LA gels exhibit a melting point, which indicates possibly use of higher temperatures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrodeposition of CuInSe2 and In2Se3 on flat and nanoporous TiO2 substrates

In₂Se₃ and CuInSe₂ films have been prepared by potentiostatic electrodeposition from deareated aqueous solutions. The substrate consisted of a duplex layer of dense and nanoporous TiO₂ obtained by spray pyrolysis deposition (SPD) and doctor blading. In₂Se₃ thin films are electrodeposited in between the TiO₂/CuInSe₂ pn heterojunction to block the electron back flow and lower the interfacial recombination produced upon illumination. The films have been characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and optical transmission. Annealing the samples in Se atmosphere is essential to improve the crystallinity of the In₂Se₃ and CuInSe₂ films. The combination of TiO₂/In₂Se₃/CuInSe₂ shows very good diode behavior with a rectification ratio higher than 100 at ±1 V.