Se Atmosphere Research Articles

Electrical properties and conduction mechanisms of ε-GaSe films for selector and phase-change memory applications

Owing to the pressing requirement for advanced memory solutions driven by explosive data growth, nonvolatile and fast-operating 1S1R structured XPoint memory has become a prominent focus, with recent interest shifting towards the 1S structured selector-only memory. The use of chalcogenide-based materials in these technologies constrains the application of such memories because of their complex quaternary compositions. This study investigated the previously unreported potential of GaSe, a simple binary Se-based chalcogenide, for applications as a selector and phase-change memory (PCM). In this study, ε-GaSe thin films were deposited using thermal evaporation and subsequently annealed in a Se atmosphere for 1 and 2 h. These ε-GaSe thin film devices incorporated metal–insulator–metal construction to exhibit both selector and PCM characteristics. The ε-GaSe device that was Se-annealed for 1 h demonstrated superior performance with a lower threshold voltage and off current, high selectivity as a selector, and reduced set voltage and reset power as a PCM. These characteristics render the proposed device a highly promising candidate for dual selector/PCM applications. To explain the electrical behavior of the ε-GaSe device, we propose the conduction mechanism model depending on the Se-annealing time, which is related to the change in the physical properties of ε-GaSe.

From non-stoichiometric CTSe to single phase and stoichiometric CZTSe films by annealing under Sn+Se atmosphere

One of the new materials for next-generation thin film solar cells is Cu2ZnSnSe4 (CZTSe). However, achieving a single-phase CZTSe compound remains a challenge. This study describes the development of Cu2ZnSnSe4 thin films through the sequential deposition of stacked films of non-stoichiometric Cu2SnSe3 (CTSe) and ZnSe by magnetron sputtering. The structural, morphological, and electrical properties as well as the surface chemistry of the films were investigated and compared depending on the growth sequence of the thin films. By using Raman spectroscopy and grazing incidence X-ray diffraction, the tetragonal CZTSe structure was confirmed. Scanning electron microscopy and energy-dispersive spectroscopy measurements of the morphological and compositional properties indicated large grains and dense surfaces with an elemental composition close to the desired stoichiometry in SLG\\SnSe2\\Cu\\ZnSe and SLG\\SnSe2\\Cu2Se\\ZnSe stacks. To ascertain the surface chemistry and unique characteristics of the produced films, additional X-ray photoemission spectroscopy experiments were carried out. The optimal band gap values for the absorber layers were found using conventional spectroscopy, and they ranged from 0.88 to 1.47 eV. According to the electrical measurements, all the films were p-type and have high carrier concentrations between 1016 and 1020 cm−3. Our findings demonstrate that employing a sequential deposition approach and annealing in different atmospheres can yield CZTSe absorber layers with desirable properties, overcoming the challenge of non-stoichiometric CTSe precursors.

Enhancement of the structural, morphological, optical and thermoelectric power factor of polycrystalline BiInSe3 thin film

There is an immediate need for thermoelectric materials that are cost-effective and readily accessible. It has been recognized that semiconductors utilizing selenium can play a pivotal role in surmounting the barriers to their extensive commercial utilization. In this study, we demonstrate the synthesis of n-type bismuth indium selenide thin films on a glass substrate using a thermal evaporation technique, followed by post-annealing in a tube furnace at 200 °C for different durations (ranging from 1 to 5 h) in a Se atmosphere. Our primary focus is on the morphological, structural, optical, electrical, and thermoelectric power factor of both the as-deposited and post-annealed BiInSe3 thin films for varying durations. Morphological, structural, and optical analyses of the BiInSe3 films were performed using a scanning electron microscope, x-ray diffraction, and UV-spectroscopy. Furthermore, we used thermoelectric measurements to thoroughly investigate the mechanism of thermoelectric transportation at room temperature, focusing on the Seebeck coefficient and charge carrier mobility concerning the formation of thin film nanostructures. By tailoring the post-annealing process, we have optimized the structural, optical, and thermoelectric power factor of BiInSe3 films, enabling thermoelectric devices for energy applications to achieve commercial maturity.

Crystalline-face-dependent photoelectrochemical properties of single crystalline CuGaSe2 photocathodes for hydrogen evolution under sunlight radiation

Photoelectrochemical (PEC) water splitting by using a electrode based on a single crystalline compound provide a good opportunity for studying on fundamental aspects of net semiconductor bulk properties related to PEC performance. In this study, single crystalline CuGaSe2 wafers exposed (321), (312), and (112) facets were used as sources of photocathodes for investigating PEC properties for water reduction into hydrogen under sunlight radiation related to their surface properties. A CuGaSe2 single crystalline ingot grown by using the zone melting method was cut along with different directions to obtain wafers with different crystal orientations. The electrical and electron-energy properties of wafers after annealing in an Se atmosphere indicated the formation of a Cu-deficient component on their surfaces when the wafers oriented (321) and (312) directions were used, whereas formation of a component was not observed on the wafer oriented in the (112) direction. Since the Cu-deficient component acted as a hole blocking layer to suppress the recombination of photoexcited carries at the heterojunction, photocathodes based on wafers having (321) and (312) orientations showed enhanced PEC performance for water reduction compared to the PEC performance of a photocathode based on a wafer having the (112) orientation. Highly active photocathodes for water reduction based on polycrystalline thin films usually have preferential (112) orientation, whereas those of densely packed powder forms would not be probable for controlling crystalline orientations. Therefore, present results would be a guide to achieve further improvements of PEC water reduction using such conventional systems.

RbF-related post-deposition treatments on Cu(In,Ga)(S,Se)2 absorbers: The role of the chalcogen atmosphere

An intriguing area in the field of alkali fluoride post-deposition treatment (PDT) on Cu(In,Ga)(S,Se)2 (CIGSSe) absorbers is the effect of the chalcogen atmosphere on the absorber’s surface during the PDT process. In this work, we focus on RbF-PDTs and we study (i) the effect of Se and S atmosphere and (ii) the impact of In and RbF co-evaporation under S vapor on the vibrational and chemical properties of the absorber’s surface. Using micro-Raman and X-ray photoelectron spectroscopy, we examine three different PDT processes: RbF under S atmosphere (RbF(S)-PDT), In and RbF co-evaporation under S atmosphere (In + RbF(S)-PDT) and In and RbF co-evaporation under Se atmosphere (In + RbF(Se)-PDT). Our results show that under Se atmosphere the formation of a Cu-poor chalcopyrite phase is enhanced, while under S atmosphere Cu-poor chalcopyrite phases are hindered. In addition, the In + RbF(S)-PDT leads to the formation of a Rb:InxSy compound at the surface of the absorber. This almost Cu –free surface compound seems to impedes Cu inclusion during the In + RbF(S)-PDT in the indium sulfide spinelle lattice thanks to the occupation of its cationic vacancies by Rb.

Optimization of the Selenization Temperature on the Mn-Substituted Cu2ZnSn(S,Se)4 Thin Films and Its Impact on the Performance of Solar Cells.

Cu2ZnSn(S,Se)4 (CZTSSe) films are considered to be promising materials in the advancement of thin-film solar cells. In such films, the amounts of S and Se control the bandgap. Therefore, it is crucial to control the concentration of S/Se to improve efficiency. In this study, Cu2MnxZn1-xSnS4 (CMZTS) films were fabricated using the sol-gel method and treated in a Se environment. The films were post-annealed in a Se atmosphere at various temperature ranges from 300 °C to 550 °C at intervals of 200 °C for 15 min to obtain Cu2MnxZn1-xSn(S,Se)4 (CMZTSSe). The elemental properties, surface morphology, and electro-optical properties of the CMZTSSe films were investigated in detail. The bandgap of the CMZTSSe films was adjustable in the scope of 1.11-1.22 eV. The structural propeties and phase purity of the CMZTSSe films were analyzed by X-ray diffraction and Raman analysis. High-quality CMZTSSe films with large grains could be acquired by suitably changing the selenization temperature. Under the optimized selenization conditions, the efficiency of the fabricated CMZTSSe device reached 3.08%.

Cu2SnSe3 phase formation from different metallic and binary chalcogenides stacks using magnetron sputtering

Cu2SnSe3 (CTSe) is a polyvalent material that can be used as an absorber layer for thin film solar cells or as a starting layer for the synthesis of CZTSe or CZTSSe compounds. Obtaining CTSe single phase films with optimized properties for thin film solar cells is a difficult task. A systematic study using both metallic and binary chalcogenides precursors for the formation of the CTSe phase was not performed. The films consisting of four different stacks (Sn\\Cu, SnSe2\\Cu, Sn\\Cu2Se, and SnSe2\\Cu2Se) were prepared by magnetron sputtering on soda lime glass (SLG) and molybdenum (Mo) coated SLG substrates, followed by annealing at 550 °C under Sn + Se atmosphere. X-ray diffraction and Raman spectroscopy results indicated the formation of a single CTSe phase in most of the stacks deposited on both substrates. Scanning electron microscopy images showed compact surfaces with large grains in the films deposited on Mo substrate, while the films on SLG have more voids on their surfaces. The elemental analysis measured by energy dispersive spectroscopy revealed stoichiometric films on Mo, and copper and tin rich compositions on SLG substrates. The band gap values inferred by conventional spectroscopy are between 0.81 and 1.95 eV. It was found that the SnSe2\\Cu and Sn\\Cu2Se stacks are preferred for the formation of a single CTSe phase, with dense surface morphology, a stoichiometric composition, and an optimal absorber layer band gap. This study opens the way to comprehend the formation reactions during the selenization of metallic and binary chalcogenides precursors towards the optimization of kesterite absorber for photovoltaic device fabrication.

Phase transformation and grain growth in spray deposited wurtzite CuInS2 films

We report the processing of large-grained chalcopyrite-CuIn(S,Se)2 (ch-CISSe) films using spray deposition of wurtzite-CuInS2 (wz-CIS) nanoparticle ink and subsequent selenization. Wurtzite to chalcopyrite phase transformation and grain growth were studied at varying selenization temperatures of 350, 400, 450, 500 and 550 °C for 15 min. On annealing in selenium (Se) atmosphere at 400 °C, the film transformed from wurtzite to chalcopyrite phase completely, while the grain growth took place at higher temperatures (500–550 °C), requiring greater amounts of Se substitution (Se/Se + S > 0.7). Differential scanning calorimetry (DSC) indicates that the phase transformation temperature is sensitive to the heating rate and has a second-order character.

Surface Modification of Cu(in,Ga)Se2 Film with a Post‐Deposition Treatment Using a KI Solution and Its Effect on Solar Cell Performance

Alkali post‐deposition treatment (PDT) of Cu(In,Ga)Se2 (CIGS) film is an effective approach to obtain high‐efficiency CIGS solar cells. Herein, a low‐cost and scalable surface passivation process is reported when the potassium iodide (KI) alkali source is employed instead of the conventional potassium fluoride (KF). CIGS surface is modified by spin‐coating of KI solution and subsequent annealing at 350 °C in a Se atmosphere. With the KI PDT, the cell efficiency is enhanced by almost 20% due to the increase of shunt resistance and the lowering of reverse saturation current. To clarify the origin of the efficiency enhancement, the chemical state and electronic structure at the CIGS surface are investigated. The KI PDT yields a valence band lowering by 0.18 eV at the CIGS/CdS interface, leading to the suppression of the interface recombination. This is possible by Cu depletion and Cu cation reduction at the CIGS surface after KI treatment. The developed process may be considered an upcoming alternative alkali PDT for CIGS absorbers. The results provide the knowledge base for further optimization of the interface properties to form high‐quality heterojunction in the CIGS solar cells.

A simple method for Ge incorporation to enhance performance of low temperature and non-vacuum based CZTSSe solar cells

Despite the slow efficiency development, Cu2ZnSn(S,Se)4 still is a promising absorber material for solar cells for its easy and low cost way of fabrication and the abundance of its elements. Similarly, also CdTe faced a long period when the record efficiency would not improve over 16.5% until a different paradigm was introduced. CZTSSe, compared to other absorbers, has the advantage that can be successfully made by solution-based growth techniques which are unique for their low cost. However this is meaningful only if selenization process is not done at high temperatures and without complicated processes. So we have optimized an easy, low cost, non-vacuum fabrication process for Cu2(Zn,Sn)(S,Se)4 thin-film absorber layers by spin coating of precursor and subsequent lower temperature selenization. A precursor solution is deposited on a Mo coated glass and the stack is then annealed below 450 °C in Se atmosphere and without the application of toxic hydrazine. With this process, we have already presented efficiencies of around 5.5%, but in this work, we introduce a simple impurity inclusion process by treating the surface of the precursor film with chlorine-based compound containing either Na, K or Ge. This allows to improve the open circuit voltage and the current density, with an increase in efficiency of 25% compared to the non-treated sample. The structural modifications are addressed by X-ray diffraction, Raman spectroscopy, atomic force microscopy and scanning electron microscopy. Current-voltage, capacitance-voltage and drive level capacitance profiling are used to analyse performance and defect density in the finished devices.

Optimization of selenization process to remove Ga-induced pin-holes in CIGS thin films

In thin-film solar cells, deposition of pinhole and the crack-free absorber layer, with the right chemical stoichiometry is highly important for high-performance solar cell devices. In solution-based CIGS solar cell technology, a nanoparticle ink approach provides phase stability of the final chalcogenide absorber layer. However, the sintering of small nanoparticles to form large grains with reduced grain boundaries is an important challenge in the fabrication process. This is usually realized by annealing in the Se atmosphere, i.e. selenization process. However, the presence of Ga in CIGS films leads to pinholes after selenization. In this study, the synthesis and deposition of high-quality films of CuInS2 (CIS) and CuIn0.75Ga0.25S2 (CIGS), are studied by using FESEM, XRD, EDS, and DLS characterization of CIGS and CIS nanoparticles and final films. We show that by selenization at reduced pressure and optimizing time and temperature, growing pinhole-free CIGS films with large grains is possible.

Influence of co-electrodeposition parameters in the synthesis of kesterite thin films for photovoltaic

Abstract Electrodeposition is one of the most attractive techniques for the synthesis of thin films chalcogenides for photovoltaic applications, in particular for earth abundant kesterite. In this work, the influence of core parameters of this technique, such as the applied potential and deposition time, on the chemical composition of co-deposited Cu–Zn–Sn precursors is studied. Indeed, how the precursor composition affects the final composition of Cu2ZnSnSe4 after reactive annealing in Se atmosphere is also investigated, not only at the film level but also in solar cell devices. X-ray based techniques (XRF and XRD) reveal that the chemical and phase composition of electrodeposited precursors is highly sensitive to small modifications (25 mV) of the applied potential during electrodeposition. Only when the applied potential is −1.2 V (vs. Ag/AgCl) the precursor composition matches to what is required for operating devices. Multi-wavelength Raman spectroscopy of selenized precursors confirms that lower potential than −1.2 V favor the formation of Sn-rich secondary and ternary compounds after selenization, while a higher overpotential led to the formation of ZnSe in the film. On the other hand, the use of longer deposition times enhance the incorporation of zinc in the film, modifies the morphology of the precursor and promotes the formation ZnSe after selenization. Photovoltaic devices were only obtained at an electrodeposition potential of −1.2 V, and reaching a maximum efficiency close to 5% for a 10 min electrodeposited CZT precursor.

Optimization of selenization parameters for fabrication of CZTSe thin film

Abstract For the formation of CZTSe films, selenization time and temperature play a crucial role in a material synthesis which in turn highly affects the properties of the films. In this work, Cu, Zn, Sn and Se were thermally-deposited sequentially on Mo coated soda-lime glass (SLG) substrates. For the formation of Cu2ZnSnSe4 (CZTSe) deposited films were annealed in a two-step process (first step 230 °C for 10 min and second step 450 °C for 5 min–30 min with 5 min interval) in Selenium (Se) atmosphere. The effect of selenization time on the structural, surface morphology, compositional, optical and electrical properties of the CZTSe films was studied. The formation of CZTSe phase is observed from XRD and Raman spectra. It was observed that with the increase in selenization time the CuSe binary phase present in the film suppressed gradually. The grain size, conductivity and mobility of the films increase whereas the band gap decreases with the increase in the hold time in the second step of selenization. The selenization time improves the properties of the films which can be suitable for solar cell applications. The study shows that optimum selenization time is essential to get a good quality CZTSe film. The device has been attempted for sample M6 and the best device obtained gives a conversion efficiency of 3.97%

Solar Cell Applications of Solution-Processed AgInGaSe2 Thin Films and Improved Properties by Sodium Doping.

Binary nanoparticle inks comprising Ag2Se, In2Se3, and Ga2Se3 were fabricated via a wet ball-milling method and were further used to fabricate AgInGaSe2 (AIGS) precursors by sequentially spraying the inks onto a Mo-coated substrate. AIGS precursors were annealed under a Se atmosphere for 1 h at 570 °C. Na2Se thin layers of varying thicknesses (0, 5, 10, and 20 nm) were vacuum-evaporated onto the Mo layer prior to the AIGS precursors being fabricated to investigate the influence on AIGS solar cells. Sodium plays a critical role in improving the material properties and performance of AIGS thin-film solar cells. The grain size of the AIGS films was significantly improved by sodium doping. Secondary ion mass spectroscopy illustrated slight surficial sodium segregation and heavy sodium segregation at the AIGS/Mo interface. Double-graded band profiles were observed in the AIGS films. With the increase in Na2Se thickness, the basic photovoltaic characteristics of the AIGS solar cells were significantly improved. The highest solar cell conversion efficiency of 6.6% (open-circuit voltage: 775.6 mV, short-circuit current: 15.5 mA/cm2, fill factor: 54.9%, area: 0.2 cm2) was obtained when the Na2Se thickness was 20 nm.

Effect of selenization temperature on the formation of CZTSe absorber layer

Cu2ZnSnSe4 (CZTSe) thin-films were deposited on soda-lime glass (SLG) and Mo/SLG substrate by the thermal evaporation method. The deposition was followed by two-step annealing in Se atmosphere. It was found that the selenization temperature significantly affects the phase, surface morphology, optical properties and electrical properties of the films. The crystallinity of the films has been improved with a variation of annealing temperature from 400 °C to 500 °C. With an increase in annealing temperature binary phase of the film also disappeared. The optical band gap of the CZTSe film has varied from 1.33 eV to 1.12 eV with the variation of selenization temperature. The impurity present in the film also reduced with the increase in selenization temperature. This work gives the idea of the effect of selenization temperature on structural, optical and electrical properties of CZTSe film deposited using thermal evaporation technique. The good-quality film obtained can be further processed for device application.

Thin films of (AgxCu1−x)2ZnSn(S,Se)4 (x = 0.05–0.20) prepared by spray pyrolysis

The recent investigation of kesterite type quaternary compounds showed that one of the main detrimental problems, which limits the efficiency of the solar cells based on these materials, is related to the high defect concentrations, mainly CuZn disorder. To overcome this problem partial replacement of Cu or Zn cations in the classical Cu2ZnSn(S,Se)4 compounds was proposed. One of the promising cations was found to be Ag, which partially replaces Cu and the solid solution of (AgxCu1-x)2ZnSn(S,Se)4 (ACZTSSe) is formed. In the present study, ACZTSSe thin films with different Ag concentrations were deposited by the spray pyrolysis method, with subsequent annealing in S + Se atmosphere. From the analysis of the chemical composition of the thin films a good correlation of measured silver concentration with initial concentration (dissolved in the main solution for deposition) for the samples with up to 15% Ag were found. These results were also confirmed by the structural studies and analysis of the Raman scattering spectra. On the other hand, thin film with higher Ag concentration (20%) has shown strong compositional inhomogeneity and presence of secondary phases was detected. Analysis of the modulated surface photo-voltage yielded the optical transition at ~ 1.5 eV, correlated with the band gap energy, and a transition at lower energy. From the temperature dependence of resistivity investigation no significant change in the resistivity for the samples with low silver concentration and strong increase for the samples with 20% of Ag were found.

Vacuum-Free and Highly Dense Nanoparticle Based Low-Band-Gap CuInSe2 Thin-Films Manufactured by Face-to-Face Annealing with Application of Uniaxial Mechanical Pressure

Copper indium gallium sulfo-selenide (CIGS) based solar cells show the highest conversion efficiencies among all thin-film photovoltaic competition. However, the absorber material manufacturing is in most cases dependent on vacuum-technology like sputtering and evaporation, and the use of toxic and environmentally harmful substances like H2Se. In this work, the goal to fabricate dense, coarse grained CuInSe2 (CISe) thin-films with vacuum-free processing based on nanoparticle (NP) precursors was achieved. Bimetallic copper-indium, elemental selenium and binary selenide (Cu2−xSe and In2Se3) NPs were synthesized by wet-chemical methods and dispersed in nontoxic solvents. Layer-stacks from these inks were printed on molybdenum coated float-glass-substrates via doctor-blading. During the temperature treatment, a face-to-face technique and mechanically applied pressure were used to transform the precursor-stacks into dense CuInSe2 films. By combining liquid phase sintering and pressure sintering, and using a seeding layer later on, issues like high porosity, oxidation, or selenium- and indium-depletion were overcome. There was no need for external Se atmosphere or H2Se gas, as all of the Se was directly in the precursor and could not leave the face-to-face sandwich. All thin-films were characterized with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and UV/vis spectroscopy. Dense CISe layers with a thickness of about 2–3 µm and low band gap energies of 0.93–0.97 eV were formed in this work, which show potential to be used as a solar cell absorber.

Investigation on the Selenization Treatment of Kesterite Cu2Mg0.2Zn0.8Sn(S,Se)4 Films for Solar Cell.

High-selenium Cu2Mg0.2Zn0.8Sn(S,Se)4 (CMZTSSe) films were prepared on a soda lime glass substrate using the sol–gel spin coating method, followed by selenization treatment. In this work, we investigated the effects of selenization temperature and selenization time on the crystal quality, and electrical and optical properties of CMZTSSe films. The study on the micro-structure by XRD, Raman, X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS) analysis showed that all CMZTSSe samples had kesterite crystalline structure. In addition, the crystalline quality of CMZTSSe is improved and larger Se takes the site of S in CMZTSSe with the increase of selenization temperature and selenization time. When increasing the selenization temperature from 500 to 530 °C and increasing the annealing time from 10 to 15 min, the morphological studies showed that the microstructures of the films were dense and void-free. When further increasing the temperature and time, the crystalline quality of the films began to deteriorate. In addition, the bandgaps of CMZTSSe are tuned from 1.06 to 0.93 eV through adjusting the selenization conditions. When CMZTSSe samples are annealed at 530 °C for 15 min under Se atmosphere, the crystal quality and optical–electrical characteristics of CMZTSSe will be optimal, and the grain size and carrier concentration reach maximums of 1.5–2.5 μm and 6.47 × 1018 cm−3.

Impact of KF-post deposition treatment on Cu(In,Ga)Se2 surface and Cu(In,Ga)Se2/CdS interface sulfurization

Partial sulfurization of Cu(In,Ga)Se2 (CIGSe) absorbers contributes to enhance photovoltaic performance of chalcopyrite based solar cells. Alternatively, KF post-deposition treatment (KF-PDT) performed under Se atmosphere has recently been used to improve the efficiency of CIGSe thin film based solar cells. In this work, we study the potential sulfurization of KF-treated CIGSe during the chemical bath deposition of the CdS buffer layer. Therefore, buried interfaces between KF-PDT CIGSe under Se or S atmosphere and CdS are investigated with the help of non-destructive and depth sensitive X-ray emission spectroscopy. No CIGSe sulfurization is detected at the absorber/CdS interface when KF treatment is performed under selenium atmosphere. In contrast, when KF treatment is done under sulfur atmosphere, partial sulfurization of CIGSe is detected at the CIGSe/CdS interface. We show through X-ray photoemission spectroscopy that the CIGSe sulfurization occurs during the KF-PDT performed under sulfur atmosphere. We also demonstrate that alkali favors greatly CIGSe surface sulfurization when the chalchopyrite is exposed to sulfur atmosphere.

Influence of the annealing atmosphere and precursor's thickness on the properties of CZTSSe based solar cells

Cu-Zn-Sn-S sulfide precursors with various thicknesses, ranging from 0.8 µm to 1.7 µm were annealed under two types of annealing atmosphere: a pure (Se) atmosphere and a mix of (S+Se) one. Pure (Se) annealing led to the Cu2ZnSn(S,Se)4 (CZTSSe) phase with a Se gradient from front to back surface. Annealing under mixture of (S+Se) improved the homogeneity of the CZTSSe solid solution across the whole layer thickness and prevented the S loss from sulfide precursor. This increased the band gap of the absorber, but enhanced the occurrence of S-rich secondary phases, mainly ZnS thin layers formed at the Mo/CZTSSe interface. The decrease of the absorber thickness can limit the occurrence of secondary phases and affects electrical parameters of the solar cells. While the best cell efficiency of 7.1% was obtained for a 1.7 µm-thick layer annealed under pure Se atmosphere, the best and homogeneous average efficiencies on 2.5 × 2.5 cm2 samples were obtained for a 0.8 µm-thick layer annealed under (S+Se) atmosphere. These results showed clearly the trade-off to find between the annealing atmosphere and the thickness of the absorber.