In this paper, Cu2SnS3 (CTS) thin film is fabricated through sulfurization of oxide precursor which is deposited by pulsed laser deposition with a mixed CuO/SnO2 target. XRD and Raman analyses indicate a pure monoclinic Cu2SnS3 phase has been obtained by sulfurization at temperature from 500 to 600 °C. A compact and smooth film with polycrystalline structure is observed through SEM result. In addition, the CTS films show excellent absorbance with the band gap around 0.91 eV estimated by UV–Vis, which is suitable for the absorption layer of solar cells. Final devices were fabricated with a SLG/Mo/CTS/CdS/i-ZnO/AZO/Al structure. Device performance is improved with the temperature increasing. The best efficiency of CTS-based solar cells is 0.69% with an open-circuit voltage of 144 mV and a short-circuit current density of 18.30 mA/cm−2.

•Cu2GeS3 is creatively synthesized from Gu-Ge alloy prepared by combustion method.•The optical band gap of Cu2GeS3 is determined to be 1.5 eV measured by UV–Vis.•The Cu2GeS3 has a proper carrier concentration of 1016 cm−3 lower than Cu2SnS3.•2.67% efficiency Cu2GeS3 solar cell is obtained with a large Voc of 592 mV.Ternary chalcogenide semiconductor copper germanium sulfide (Cu2GeS3) composed of earth-abundant and non-toxic elements is considered to be a suitable light harvesting material for photovoltaics. In this study, Cu2GeS3 thin film solar cells are creatively fabricated based on combustion method. XRD and Raman analyses reveal that the combustion synthesized product is composed of Cu-Ge alloy rather than metal oxides. The structural, morphological, optical and electrical properties of CGS films are analyzed in detail. The best power conversion efficiency of Cu2GeS3 thin film solar cell achieve 2.67% with a high open-circuit voltage of 592 mV. The experiment results reveal that the p-type semiconductor Cu2GeS3 is an extremely promising light harvesting material for photovoltaics due to its suitable band gap and carrier concentration.

•CZTS thin film solar cell with 4.94% efficiency was prepared by PLD method.•The quaternary PLD target was fabricated by innovatively using of combustion method.•CZTSSe absorber layers with tunable S/(S+Se) ratios were prepared by SAS method.•The beneficial band gap grading was introduced by the application of SAS method.Cu2ZnSn(SxSe1−x)4 thin film solar cells have been fabricated by pulsed laser deposition using single quaternary oxide target prepared by combustion method. Compared with the traditional ball milling process, the innovative application of combustion method on preparing PLD target greatly ensures the homogeneous distribution of chemical compositions in the deposited film. The improved selenization after sulfurization (SAS) method is successfully employed to synthesize Cu2ZnSn(SxSe1−x)4 absorber layers with different x values. The effects of S/(S+Se) ratio on the structural, morphological, optical properties of absorber layers and the final performance of the cells are studied in detail. Combining the results of x-ray diffraction and UV–vis spectra, the beneficial band gap grading is considered to exist in the annealed Cu2ZnSn(SxSe1−x)4 films. The best power conversion efficiency of 4.94% is achieved by pure Cu2ZnSnS4 thin film solar cell with a short circuit current density of 16.82 mA cm−2 and a high open circuit voltage of 684 mV.

•Cu2ZnSnS4 thin film solar cells were creatively fabricated by the combustion method.•A low-cost non-vacuum method was adopted using highly pure precursor powder.•We present a probable formation mechanism of Cu2ZnSnS4 for metal oxides system.•Secondary phase with narrow band gap will decrease the band gap of Cu2ZnSnS4.A novel route that fabricate Cu2ZnSnS4 solar cells by a combustion method has been successfully conducted. The probable formation mechanism of Cu2ZnSnS4 for metal oxides system during the sulfurization process is analyzed in detail through the phase analysis in several continuous temperature ranges in combination with thermodynamic calculation. The effects of annealing temperature on the structural, morphological, compositional and optical properties of absorber layer were studied. The UV–vis spectra revealed the band gap of as-prepared thin films varying from 1.48 to 1.34 eV along with rising the sulfurization temperature. It was found that secondary phase with narrow band gap significantly affects the band gap of Cu2ZnSnS4. The best performance of the Cu2ZnSnS4 thin film solar cells prepared by the combustion method achieved a powder conversion efficiency (PCE) of 1.6% with a short circuit current density of 10.5 mA/cm2 and an open circuit voltage of 505 mV. This low-cost non-vacuum technique has a promising application in synthesis of light-absorbing layers for photovoltaic devices, which can vastly reduce the costs and simplify the preparation process.

•Stacked SnS/Cu layers byCBD were used to fabricate CTS solar cells.•Monoclinic CTS thin film with Cu/Sn=1.68 was demonstrated in this study.•Mo/SnS/Cu stacked order of layers was found to produce most efficient solar cell.•Up to 1% efficient CTS solar cells were obtained with high Jsc of 19.2 mA cm−2.In present study, monoclinic Cu2SnS3 crystalline thin films have been successfully fabricated for the first time using stacked layer SnS/Cu by a CBD–annealing route. The chemical composition, stack order and effects of annealing temperature on Cu2SnS3 thin films and devices have been studied in detail. SEM, XRD, Raman, EDX and UV–vis analyses indicate that Cu2SnS3 absorber layers fabricated by this CBD–annealing route have good morphology, monoclinic crystal structure, relatively proper elements composition (Cu/Sn=1.68) and band gap (Eg~0.87 eV). Furthermore, the photovoltaic cells based Cu2SnS3 thin films have been prepared using CBD for the first time and the device with the order of Mo/SnS/Cu annealed at 600 °C for 10 min with S powder shows the best performance, nearly 1% efficiency (Voc: 157 mV, Jsc: 19.20 mA cm−2, and FF: 31.9%). Alternative approach to produce low-cost and large-scale solar cells may be provided by this CBD–annealing route without the need for expensive vacuum-based deposition equipment.

•Cu and CuS are introduced and compared in fabrication of CZTS based solar cells.•CZTS thin films fabricated by stack SnS/Cu/ZnS show better morphology.•CZTS solar cells annealed by stack SnS/CuS/ZnS with Sn powder show better performance.•3.79% efficient CZTS solar cell was obtained by CBD method with stack SnS/Cu/ZnS.In this study, two types of Cu source, namely Cu and CuS, are introduced and compared in fabrication of Cu2ZnSnS4 thin films and solar cells with stacked layers SnS/Cu(S)/ZnS by CBD-annealing route, including the comparison of morphologies, chemical composition, phase structure and photoelectric properties. The results show that Cu2ZnSnS4 thin films with high quality of morphology and phase purity that fabricated by stack SnS/Cu/ZnS are more proper for the high performance of Cu2ZnSnS4 thin film solar cells. The Cu2ZnSnS4 solar cells fabricated with the stack SnS/Cu/ZnS by chemical bath deposition-annealing route exhibit an improved conversion efficiency of 3.79% relative to that using the stack SnS/CuS/ZnS.

•Sb2Se3 thin film were fabricated by selenizing the metal precursors deposited by sputtering.•We compared different Sb2Se3 thin films prepared by different thermal process.•We investigated the temperature effect of grain growth for Sb2Se3 thin film by Rapid Thermal Process.•We fabricated Sb2Se3 solar cell as the same structure as CIGS thin film solar cell and achieved an efficiency of 3.47%.Sb2Se3 thin films have been grown on Mo-coated glass substrate by rapid thermal process (RTP). In this paper, we investigate the effects of annealing temperature on selenizing metal precursor deposited by sputtering method. At optimized temperature, the best performed devices with the same structure as CIGS solar cells achieved the efficiency of 3.47% with an open circuit voltage of 414 mV. This study provides a guideline to fabricate Sb2Se3 thin film by RTP and possibility in large scale industry application.

•A presulfurization step is creatively used in combination with combustion method.•Precursor layers composed of Cu-Zn-Sn-S and Cu-Zn-Sn-O are compared.•The carrier concentration of CZTS is measured to be 2.4×1016 cm−3 by C-V method.•The experiment process is common to other Cu-based kesterite solar cells.In this study, a pulsed laser deposition process using single quaternary sulfide target to fabricate Cu2ZnSnS4 thin films was described. The mixed metal oxides powder prepared by combustion method was further utilized to fabricate quaternary CZTS target by adopting a presulfurization step. In addition, CZTO target directly made from combustion synthesized oxide powder was also fabricated as comparison to study the effects of precursor composition form on the grain growth and absorber/Mo interface properties. The carrier concentration of the annealed Cu2ZnSnS4 film was determined by capacitance-voltage measurement.

•Cu/SnS precursors was fabricated by CBD with ARR.•Firstly to investigate the growth mechanism of CTS with Cu/SnS precursors.•Initial Cu2−xS and succedent Cu8S5 from decomposing of CuS react with SnS forming CTS.•Tetragonal CTS transform to monoclinic CTS according to Raman date at 430 °C.Cu2SnS3 is one kind of new promising material for low-cost thin film solar cells. In this letter, Cu2SnS3 film has been fabricated through sulfurization of Cu/SnS precursors stacked layers by Chemical bath deposition(CBD) with rapid thermal system. To study the growth mechanism of CTS, the phase structural and micro-structural properties of the films with different annealing temperature were taken out carefully. In brief, binary sulfide Cu2−xS forms at low temperature and decomposes to Cu8S5 with the increase of annealing temperature showed by XRD analysis. Gradually, top binary sulfide layer disappears with the generation of Cu2SnS3, which is consistent with the result of SEM that the boundary line disappears with the temperature rising. Moreover, Raman analysis confirms that tetragonal Cu2SnS3 begins transforming to monoclinic Cu2SnS3 at 430 °C and monoclinic Cu2SnS3 is obtained at 500 °C.

Sb2Se3 with suitable bandgap and non-toxic, abundant composition represents a promising absorber material as a replacement for Cu2ZnSnS4 and Cu(In,Ga)Se2 for thin film solar cells. In this paper, we investigated the effect of annealing temperature on selenizing metal precursor deposited by sputtering. With optimized temperature, the best performance of the devices achieved the efficiency of 0.72 % with an open circuit voltage of 368 mV. This study provide the guideline to fabricate Sb2Se3 thin film solar cell as the same structure as CIGS.

•Stacked layer by a CBD method was introduced to fabricate CZTSSe/CZTS solar cells.•3.0% and 2.2% efficiency of CZTSSe/CZTS solar cells were obtained.•The order of ZnS/Cu/SnS/Mo was demonstrably proper for a CBD-annealing route method.•ARR was introduced to deposit Cu thin film during the deposition of stacked layer.A novel idea that using chemical bath deposition-annealing route for preparing absorber films of the Cu2ZnSnS4−xSex solar cells with stacked layers (ZnS/Cu/SnS) was proposed and carried out in this study. The absorber layers fabricated by this new method were demonstrably proper for solar cell devices. The solar cells based on the as-synthesized Cu2ZnSnS4−xSex/Cu2ZnSnS4 layers showed high photoelectric transformation efficiency, nearly 3.0% and 2.2% with the large area 1.27 cm2 and 1.80 cm2, respectively. The new method introduced here based on chemical bath deposition without the complexity of vacuum equipment may provide an alternative approach to produce large area solar cells for practical application. In addition, during the deposition of the stacked layers, a new concept called Assistant Reduction Reaction was firstly carried out to deposit metallic Cu thin film on the SnS film, which acted as not only a substrate, but also an assistant reductive agent. If the present technique is properly extended, it is possible for the preparation of other metal thin films for practical application.

•The influences of Na on the crystalline and electrical properties of Cu2ZnSnSe4 have been systemically studied.•Na was incorporated into the CZTSe films by PLD system to accurately control the concentration of Na element.•The sodium incorporation had positive effects on the performances of solar cell.•With the superfluous alkalis doping, the cell performances decreased quickly.In this paper, the influences of Na on the crystalline and electrical properties of Cu2ZnSnSe4 have been systemically studied. Na was incorporated into the CZTSe films with two different substrates (SiO2/Si and Mo coated Soda-lime-glass) by pulse laser deposition to accurately control the concentration of Na element. The results showed that the sodium incorporation had positive effects on the performances of solar cell based on the as-prepared CZTSe absorber layer, including the open circuit voltage, short circuit current, fill factor and thereby power efficiency. But, with the superfluous alkalis doping, the cell performances decreased quickly, which have been systemically studied to investigate the influences of Na doping on the crystalline and electrical properties of absorber layer and to get the optimal alkalis doping concentration.

•A simple low cost universal method is introduced to fabricate multi-element films.•Cu2MSnS4 (M:Cd,Mn) thin films are firstly fabricated by CBD- annealing route.•XRD and Raman indicate that Cu2MSnS4 (M:Zn,Cd,Mn) are almost pure phase.•The bandgaps of Cu2MSnS4 (M:Zn,Cd,Mn) are 1.41, 1.07 and 1.45 eV, respectively.•Composition can be easily controlled by adjust the thickness of each stacked layers.In this letter, a simple and low cost route is proposed to fabricate Cu2MSnS4 (M: Cd, Mn) thin films. As a comparison, Cu2MSnS4 (M: Zn) is also listed. The precursor films of Cu2MSnS4 (M: Zn, Cd, Mn), stacked as SnS, Cu, and ZnS(CdS or MnS), are deposited by the CBD method, along with a subsequent sulfurization heat treatment. All films show good morphology, analogous crystal structure, strong optical absorption characteristics and proper values of band gaps (CZTS-1.41 eV, CCTS-1.07 eV and CMTS-1.45 eV) for thin film solar cells, which suggest that the high quality Cu2MSnS4 (M: Zn, Cd, Mn) thin films can be easily obtained by this CBD-annealing route. If the present technique was properly extended, it would be also possible for the low cost and large-scale preparation of other multi-elements thin films with stacked layers for practical application.

•CuInS2 thin film was fabricated by sulfurization the oxides based precursors.•Through high-temperature sulfurization, the metastable CuAu ordered phase is avoided.•The high quality CuInS2 thin film with nearly pure chalcopyrite structure is obtained.In this letter, a low-cost non-vacuum process is introduced to fabricate the pure crystalline chalcopyrite (CH) CuInS2 thin films. Since the Chalcopyrite (CH) and CuAu (CA) ordering phases have very close formation energy and structures and tend to coexist in CIS films, it is very difficult to get single-phase chalcopyrite CIS in normal way. Simply, in this study, the high-temperature sulfurization of copper indium oxide nanoparticles precursor layers has been taken out and the presence of the metastable CuAu (CA) ordering phase is successfully avoided in the chalcopyrite CIS thin films. In addition, films sulfurized at high temperature show pure chalcopyrite phase, good crystallization and reliable optical properties, which are suitable for preparation of high efficiency solar cells.

•Solvent-free synthesis of binary sulfide nanoparticles for CZTS and CZTSSe thin films has been described.•Cu, Zn, Sn sulfides nanoparticles are synthesized via a facile, solvent-free route, which is low cost and easy to scale-up.•The influences of incorporation of sulfur/selenium on the CZTS/CZTSSe films have been investigated.A low-cost non-vacuum process for fabrication of Cu2ZnSnS4 (CZTS) and Cu2ZnSn(SxSe1−x)4 (CZTSSe) films by solvent-free mechanochemical method and doctor blade process is described. First, CuS, ZnS and SnS nanoparticles are synthesized via a facile, solvent-free route, which is low cost and easy to scale-up. Second, the sulfides nanoparticulates precursors are deposited in a thin layer by doctor blade technique. Finally, the dry layers are sintered into CZTS/CZTSSe thin films. Different annealing processes are used, and the influences of incorporation of sulfur/selenium on the CZTS/CZTSSe films have been investigated. These structure, morphology and optical properties of CZTS/CZTSSe films are suitable for thin film solar cell fabrication.

•Densification studies were performed to improve the grain size and morphology of the oxides derived CZTSe films.•The CZTSe films showed the dominant CZTSe structure without ZnSe and Cu2SnSe3 secondary phase.•The compressed and untreated CZTSe films showed the Kesterite and Stannite structure respectively.Cu2ZnSnSe4 (CZTSe) films were prepared by selenization of oxides nanoparticles. A novel densification method was performed to improve the grain size and morphology of the CZTSe films. From absorption spectroscopy measurement, it was also found that the compressed CZTSe films showed Kesterite structure with a band gap of 0.92 eV, while the untreated CZTSe films showed partially disordered Kesterite structure with a band gap of 0.86 eV. The phase transition during the selenization of oxides nanoparticles is affected significantly by the compact density. The nucleation and growth of Kesterite phase is considered to be facilitated by the mass transfer around the particle contacts. The different characterization techniques show that the dense CZTSe layer with very large grain size can be achieved by using compression method.

CuInSe2 thin films have been synthesized by selenization of co-sputtered Cu-In precursors using rapid thermal processing (RTP). Heat treatments from 400 to 450 °C for periods between 1 min and 10 min were carried out on (Cu-In)/Se precursors. Phase evolution as function of reaction temperature and holding time was analyzed according to XRD and SEM results. Severe Se loss during RTP was proved in our experiments and has been reported by many other researchers. To solve the problem, a new effective way of reducing Se loss was presented, which is based on low temperature heat treatment at 250 °C before high temperature annealing. Nearly single-phase CuInSe2 thin films have been achieved by annealing precursors at 250 °C for 5 min then 450 °C for 1 min. Se loss can be significantly reduced via low temperature heat treatment by the fact that under 250 °C, Se is evaporated mildly and largely consumed as Cu-Se and In-Se binary selenides.

Undoped ZnO film was obtained at ambient temperature using magnetron sputtering and further annealed in vacuum and oxygen atmosphere. A (103) texture was observed on the surface of as-deposited (002)-preferred ZnO film. XPS shows that the majority zinc remains in the valence state of Zn2+, meanwhile the close inspection of O 1s shows that O 1s is composed of components including OI, OII and chemically- or physically-adsorbed oxygen. By the relative intensity of OI/OII and broadened OI the oxygen vacancy concentration variation was considered in different annealing processes. Since the Zn atoms are mostly located in the ZnO1−x matrix, the (002) peak shift in the XRD of the vacuum- and oxygen-annealed films is attributed to the variation of the oxygen vacancy concentration, suggesting that the oxygen vacancies in the ZnO thin films are responsible for the decrease of the lattice parameters.Highlights► (002)-preferred ZnO thin film was deposited at ambient temperature with good quality. ► (103) texture was observed on the surface of the as-deposited film. ► VO concentration variation in the annealed films was confirmed from XPS O 1s analysis. ► VO was supposed to decrease the lattice parameter in the ZnO film.