CCTS Films Research Articles

Structural and transport properties of Cu2CoSnS4 films prepared by spray pyrolysis

In the present work, stannite Cu2CoSnS4 (CCTS) films were elaborated using spray pyrolysis method on soda-lime glass, at different deposition temperatures (Td = 250, 300, and 350 °C), followed by different chosen sulfurization temperatures (Ts = 450, 500, and 550 °C). X-ray diffraction (XRD) revealed the nearly single-phase formation of CCTS films at 300 °C deposition temperature. After sulfurization in argon flow, the XRD lines become narrower, the average crystallite size expanding above 70 nm. The Raman spectroscopy analysis confirmed the stannite structure formation, as well as the presence CoS2 secondary phases, which reduces at higher sulfurization temperature (550 °C). The energy dispersive spectroscopy results indicated atomic ratios of Cu/Co/Sn/S close to the ideal stoichiometric ratio 2:1:1:4. The room temperature photoluminescence emission is recorded with maximum in the 1.35–1.40 eV range. Thermoelectric properties are measured up to 130 °C, the films show poor power factor as a result of small positive Seebeck coefficients 10–45 μV K−1 and low electrical conductivity despite of having relatively high carrier concentration (∼1020 cm−3).

Metal work function enabled modulation on photo-detective properties for flexible Cu2CoSnS4 films with different annealing time

Herein, direct solution spin coating-based earth-abundant quaternary Cu2CoSnS4 films are reported to achieve cost-effective, visible photodetectors on flexible polyimide (PI) substrates. Different annealing times and metal work functions effectively control the optoelectronic properties of flexible CCTS films. Furthermore, the photosensitivity (50 ± 4)%, photoresponsivity ((1090 ± 15) mA/W), and specific detectivity ((2.38 ± 0.21) × 1010 Jones) are exhibited for CCTS photodetectors with Au electrodes, along with composition ratio of (Cu/(Co + Sn) = 0.88) and 400 °C for 2 h condition. This implies that understanding process conditions and their mechanism can be beneficial for securing high-performance, flexible, visible photodetectors.

Temperature-Time profile effects on evolution of physical and electronic properties in visible light Cu2CoSnS4 photodetectors

Earth-abundant quaternary chalcogenide Cu2CoSnS4 (CCTS) films on soda-lime glass (SLG) substrates are prepared via non-vacuum, cost-effective direct solution spin coating technique. The phase formation mechanism of CCTS films is investigated via TGA, FTIR, XRD, and RAMAN characterization. Annealing temperature effects on the crystalline phase, chemical composition, and grain growth, strongly linked with electrical and photodetection parameters of CCTS films, are systematically investigated through XRD, Raman, FEG-SEM, and EDS analysis. Through the transfer length measurement (TLM) method, the electrical properties of CCTS films annealed at 575 °C exhibit noticeable 92% reduction of both contact resistance (Rc) and resistivity (ρ), compared to those of the film processed at 300 °C. The highest photoresponsivity (7.50 A/W) and specific detectivity (4.70 × 1010 Jones) of CCTS devices have been demonstrated with annealing conditions at 575 °C and a bias voltage of 10 V as well. The present study reveals the impact of both annealing temperature and bias voltage on photodetector performance.

Cu/(Co+Sn) ratio effects on physical and photodetective properties for visible light absorbing Cu2CoSnS4 nanoparticles via a one-pot hydrothermal process

The composition ratio plays a vital role in modulating the thermal, magnetic, and optoelectronic properties of earth-abundant quaternary chalcogenides. Here we report on an impact of Cu/(Co + Sn) ratio on secondary phase formation, size, and shape of Cu2CoSnS4 (CCTS) nanoparticles synthesized via monoethanolamine (MEA) promoted the hydrothermal process. The CCTS phase formation mechanism is experimentally elucidated by a time-dependent synthesis study during a one-pot facile hydrothermal reaction, and it is confirmed by using X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) analysis. The morphology, particle size distribution, and shape of synthesized nanoparticles are examined by field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) analysis. The N-Methyl-2-pyrrolidone (NMP) solvent-based CCTS paste was drop-casted on a thermally oxidized silicon wafer (∼100 nm SiO2) to form films. The increase in optical bandgap from 1.48 eV to 2.00 eV is observed for an increase in Cu/(Co + Sn)) ratio of prepared CCTS films. The electrical, photodetection properties of the prepared films with respect to the (Cu/(Co + Sn)) ratio under dark and light illumination are studied. The lowest sheet resistance (Rsh= (13.56 ± 0.9) × 103 Ω/cm) and contact resistance (Rc= (108.31 ± 3.43) × 103 Ω) is obtained for devices made with a higher value of Cu/(Co + Sn) ratio = 1.17. On the other hand, the highest photosensitivity (Sph = 32%), photoresponsivity (Rph = 75.58 mA/W), and detectivity (Dph = 1.44 × 108 Jones) are demonstrated for device assembled with the lowest ratio (∼0.86) of Cu/(Co + Sn). The present study reveals that Cu/(Co + Sn) ratio affects a significant impact on such as a phase, morphology, chemical compositional ratio of nanoparticles, optical, electrical, and photoresponsive properties of prepared films.

Development and characterization of photodiode from p-Cu2CdSnS4/n-Bi2S3 heterojunction

Here we investigated the photo response behaviour of p-Cu2CdSnS4 (p-CCTS)/n-Bi2S3 heterojunction photodiode. The solution processed CCTS films without any high temperature sulfurization demonstrated the photo response behaviour, suggesting the material is well suited for low temperature processed photovoltaic applications. A CCTS film was deposited on an ITO coated glass substrate using simple sol-gel based spin coating method. Current–voltage (I–V) characteristic of the p-CCTS/n-Bi2S3 heterojunction photodiode showed a good rectifying behaviour indicating better junction formation between CCTS and Bi2S3 layers. The obtained photocurrent is 4 times higher than that of the dark current. The I–V curves are asymmetric with respect to voltages and the photocurrent in the positive bias region is considerably higher than the corresponding values in the negative bias region. With these results, it is concluded that the CdS material in traditional thin film PV devices can be replaced with Bi2S3 for better transportation of charge carriers in the PN-junction.

Highly crystalline, large grain Cu2CoSnS4 films with reproducible stoichiometry via direct solution spin coating for optoelectronic device application

Abstract Highly crystalline, large grain Cu2CoSnS4 (CCTS) films with reproducible stoichiometry were implemented on thermally oxidized Si wafers and soda lime glass (SLG) substrates via direct solution spin coating. Effects on Cu concentration in the formation of CCTS phase were systematically investigated by X-ray diffraction (XRD) and Raman spectroscopy. Moreover, CCTS films, processed with the optimized Cu concentration (∼8 mmol) and annealing temperature of 575 °C in Ar ambient, exhibit the film morphology with compact, dense, and large grains up to the size of 1.5 μm. The resistivity (ρCCTS) of CCTS films on SLG and SiO2 substrates were extracted as 7.15 ± 0.18 Ωcm and 7.8 ± 0.19 Ωcm, respectively, denoting that surface roughness and sodium diffusion might affect electrical conductivity of CCTS films. Furthermore, for the optimized CCTS films, noticeable relative photosensitivity (Sph) up to 20% was achieved under red LED illumination, highlighting that CCTS films could be promising for cost-effective thin film solar cells.

Synthesis and characterization of Cu2CoSnS4 thin films prepared via radio-frequency (RF) magnetron sputtering

Cu2CoSnS4 (CCTS) thin films, for the first time, were successfully fabricated by RF magnetron sputtering with two different metal precursor stacking sequences followed by sulfurization treatment under kinds of temperatures. Structure, morphology, composition, chemical valence states and optical properties of the as-grown films were discussed by X-ray diffraction (XRD), Raman spectroscopy (Raman), Scanning electron microscopy (SEM), Energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible-near-infrared spectrophotometer (UV–vis–NIR spectrophotometer) respectively. XRD and Raman analysis indicated that the as-obtained Cu2CoSnS4 thin films possess a stannite structure and the crystallinity was improved accompanying the incremental sulfurization temperature under both two depositing orders. The growth mechanism of CCTS films during vulcanization process was also discussed. XRD, Raman spectroscopy and SEM analysis showed that the precursors deposited in Cu/Co/Sn sequence had the best crystallinity after 600 °C sulfurization annealing. Under this preparation condition, XPS analysis showed that the chemical states of the four main elements in the film were Cu (I), Co (II), Sn (IV) and sulfide ions,and it exhibited the direct band gap of 1.58 eV by UV–vis–NIR absorption spectra, which is close to the ideal values for photovoltaic utilization.

Annealing temperature and stabilizer effects on morphological evolution of Cu2CoSnS4 films on thermally oxidized Si wafers via direct spin-coating

Earth abundant copper based quaternary chalcogenide Cu2CoSnS4 (CCTS) films were processed by using nontoxic, direct solution-spin-coating process on thermally oxidized Si wafers. Monoethanolamine (MEA) stabilizer effects on chemical composition, crystalline phase, and morphology of the CCTS films were investigated. A systematic study on crystal phase, chemical composition and film morphology evolution including grain size and crack formation, corresponding to annealing condition, were performed via X-ray diffraction, FEG-SEM, and energy dispersive spectroscopy. The cracks free CCTS films were obtained at annealing temperature (T > 550 °C). The electrical properties of two-terminal CCTS devices processed at different annealing conditions were systematically analyzed by transfer length method (TLM) patterns. The lower resistivity (ρ∼39.66 Ωcm) and contact resistance (Rc∼12.3 ± 26 kΩ) for CCTS films annealed at 550 °C, as compared to low annealing temperature, were extracted and validated with CCTS film thickness and grain sizes supported by XRD and SEM studies.

Fabrication of Cu2CoSnS4 thin films by a facile spray pyrolysis for photovoltaic application

The role of substrate temperature on the structural, morphological, optical, and photovoltaic properties of Cu2CoSnS4 (CCTS) thin films based on earth abundant and non toxic elements, has been presented. Thin films of CCTS have been deposited by spray pyrolysis technique. X-ray diffraction study revealed that the films are polycrystalline in nature with stannite structure. Raman analysis confirmed the phase purity of CCTS films deposited at substrate temperature of 350°C. The XPS spectra indicates oxidation states of Cu, Co, Sn, and S to be Cu+, Co2+, Sn4+, and S2− in CCTS films. FE-SEM images showed drastic variation in the morphology of the films with respect to increase in substrate temperature. EDAX spectra of the films deposited at different substrate temperatures revealed the presence of different constituent elements such as, Cu, Co, Sn and S in CCTS thin films. The energy band gap values for the films were found to be decreasing from 1.79eV to 1.42eV with respect to increase in substrate temperature. The static contact angle measurement of the films with Sodium sulphate electrolyte depicts the hydrophilic nature of the films. The photoelectrochemical solar cell has been constructed using Sodium sulphate as electrolyte, platinum as counter electrode, while CCTS thin films were used as working electrodes. The power conversion efficiency of 1.78 % and open circuit voltage of 350mV was observed for the CCTS thin films deposited at substrate temperature of 350°C.

Temperature dependent properties of spray deposited Cu2CoSnS4 (CCTS) thin films

A modified spray pyrolysis technique was employed for the deposition of Cu2CoSnS4 (CCTS) thin films. X-ray diffraction study showed that the CCTS thin films exhibit stannite structure with preferred orientation along (112) plane. The phase purity of sprayed CCTS films was confirmed from Raman analysis, as the most intense peak is observed at 320 cm−1 corresponding to A1 mode. With increase in substrate temperature the grains over the surface of the CCTS films become more distinct. The EDAX spectrum revealed the presence of different constituent elements such as, Cu, Co, Sn and S for the films deposited at 325 °C. The optical absorption study showed that the energy band gap values of the CCTS films are decreasing from 1.70 to 1.46 eV with respect to increase in substrate temperature from 275 to 325 °C.

Effect of Cd content and sulfurization on structures and properties of Cd doped Cu2SnS3 thin films

In the present work, we fabricated solid solution of Cd in the Cu2SnS3 (CTS:Cd) and Cu2CdSnS4 (CCTS) thin film by Cd doping in the Cu2SnS3 (CTS) with a simple solution approach and sulfurization process, and investigated the effects of Cd content and sulfurization on crystalline structure and quality as well as bandgap (Eg). It was found that a face-centered cubic CTS (C-CTS) film with Eg of 0.82 eV can be prepared by the solution approach. The C-CTS transformed into CTS:Cd with tetragonal structures (T-CTS:Cd) when the Cd contents are in the range of 4.18–13.38 at%, and further transform into T-CTS:Cd and CdS as the Cd content is between 13.38 and 19.57 at%. The Eg can be tuned from 0.82 to 1.26 eV by changing the Cd doping content for the as-fabricated samples. The sulfurization process made the C-CTS dissolve into C-CTS and T-CTS, and the T-CTS:Cd transformed into the CCTS in the Cd content of 7.30–13.54 at%. A single phase of CCTS film with Eg of 1.37 eV was obtained in the content of 10.18–13.54 at%. The sulfurization process can change crystalline structure, improve crystalline quality and tune band gap of the CTS and CCTS films at the same Cd doping content compared with the as-prepared films. It is believed that the single phase of C-CTS, T-CTS:Cd and CCTS films will be promising absorber materials of solar cells.

Photo-electrochemical properties and electronic band structure of kesterite copper chalcogenide Cu2–II–Sn–S4 (II = Fe, Co, Ni) thin films

Kesterite CFTS, CCTS and CNTS thin films have good electrocatalytic behavior and improved photoelectrochemical responses with respect to a ZnO nanorod counter electrode.

Mechanism of effect of intrinsic defects on electrical and optical properties of Cu2CdSnS4: an experimental and first-principles study

Near stoichiometric and Cd-poor Cu2CdSnS4 (CCTS) thin films with p-type conductivity were prepared by magnetron sputtering and post-sulfurizing. It is found that the hole concentration of the Cd-poor CCTS is two orders of magnitude higher than that of the near stoichiometric CCTS while its optical bandgap is smaller than the near stoichiometric CCTS’. It is suggested by using first-principles calculations that the dominant intrinsic defects are Cu vacancy (VCu) and fully passivated defect complex of 2CuCd+SnCd in the Cd-poor CCTS, but VCu and CuCd in the near stoichiometric CCTS. The VCu is responsible for the p-type conductivity of both CCTS films, while the 2CuCd+SnCd complex for smaller bandgap and higher hole concentration of the Cd-poor CCTS. The mechanism of effect of the intrinsic defects on the optical and electrical properties of the CCTS is suggested in the present paper.

Solution Processed Cu2CoSnS4 Thin Films for Photovoltaic Applications

Earth abundant alternative chalcopyrite Cu2CoSnS4 (CCTS) thin films were deposited by a facile sol–gel process onto larger substrates. Temperature dependence of the process control of deposition and desired phase formations was studied in detail. Films were analyzed for complete transformation from amorphous to polycrystalline, with textured structures for stannite phase, as reflected from the X-ray diffraction and with nearly stoichiometric compositions of Cu:Co:Sn:S = 2:0:1:0:1:0:4:0 from EDAX analysis. Morphological investigations revealed that the CCTS films with larger grains, on the order of its thickness, were synthesized at higher temperature of 500 °C. The optimal band gap for application in photovoltaics was estimated to be 1.4 eV. Devices with SLG/CCTS/Al geometry were fabricated for real time demonstration of photoconductivity under A.M 1.5 G solar and 1064 nm infrared laser illuminations. A photodetector showed one order current amplification from ∼1.9 × 10–6 A in the dark to 2.2 × 10–5 A and...