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In this work, antimony selenide (Sb2Se3) thin films were prepared using electron-beam (e-beam) evaporation followed by selenization process (two-step method) for the first time. The effect of selenization temperature on the properties of Sb2Se3 thin films and solar cells was investigated systematically. Formation of pure polycrystalline Sb2Se3 was confirmed and the intensity of (hk1) and (hk2) patterns was found to decrease while that of (hk0) to increase with temperature elevating. However, when the temperature became higher than 360 °C, the shape of Sb2Se3 grains gradually changed to rod-like shape from round shape and some craters and cracks in the films can be observed. Sb2Se3 films prepared at 360 °C showed an average grain size of 450 nm, a roughness of 42 nm, an optical bandgap of 1.24 eV and a carrier concentration of 4.99 × 1012 cm−3. The corresponding Sb2Se3 solar cells exhibited an optimal power conversion efficiency of 1.15%. Our results demonstrated that the process of e-beam evaporation of Sb followed by selenization at appropriate temperature is a good way to prepare high quality Sb2Se3 thin films for solar cells. [ABSTRACT FROM AUTHOR]

Flexible Cu(InGa)Se2 (CIGS) solar cells on metallic substrates are highly desirable for versatile energy applications. However, related researches reported on CIGS devices usually used a diffusion barrier, which involves an issue of thermal expansion coefficient matching and complicates the fabrication process. In this study, CIGS solar cells were fabricated on Ni and Ti foils through selenization of metal stacks deposited by e-beam evaporation, without the use of diffusion barrier. The films on Ti foils showed (112) preferred orientation while those on Ni foils exhibited (220) preferred orientation, due to the different crystal orientation of substrates. In–Ni and Ga–Ni phase were observed in films prepared on Ni foils, which led to the existence of Cu2–xSe. As a result, the CIGS solar cells fabricated on Ni foils showed inferior photoelectric properties, whereas those on 50 and 100 μm Ti foils presented conversion efficiency of 4.9% and 6.6%. The discrepancy on efficiency between two cells on Ti foils was ascribed to the different structural properties induced by the thermal stress. After 100 bending cycles, efficiency of cells on 50 and 100 μm thick Ti foils decreased by 1.0% and 2.6% respectively, indicating that CIGS solar cell on 50 μm Ti foil is more promising as flexible device applied on harsh circumstance. [ABSTRACT FROM AUTHOR]

Two-step process is considered to be more simple than co-evaporation method in Cu(InGa)Se2 (CIGS) thin films preparation process. However, research on CIGS thin films prepared by two-step process based on evaporation of elemental metals Cu, In and Ga is hardly reported. In this work, four types of metal stacks engineered as In/Ga/Cu/Ga/In (type A), Cu/Ga/In (type B), Cu/In/Ga (type C) and Cu/Ga/In/Cu (type D) were prepared and effects of metal stack precursors on properties of CIGS thin films formed by two-step process were studied. All types of precursors consisted of Cu-In, Cu-Ga and In phases. CIGS thin film from type A precursor showed poor compactness and relative high surface roughness due to the ordered defect compounds on the surface. Type B precursor exhibited a better compactness and crystal quality which led to an optimal structural property of films among all types of CIGS thin films. The reduction of Ga/(Ga + In) and the gaps appeared at the Mo/CIGS interface of CIGS thin film from type C precursor were explained by the re-evaporation of Ga element and compensation of In element during selenization. Grain size in CIGS thin film from type D is a little smaller than that from type B. Models of selenization process in different types of precursors were given. CIGS solar cell from type B exhibited the highest conversion efficiency of 9.2%. [ABSTRACT FROM AUTHOR]

Abstract It is considered that alkaline elements (such as Na, K, Rb) introduced through post-deposition treatment are able to modify the near-surface region of Cu(InGa)Se 2 thin films. However, research on the effects of Ca element on properties of Cu(InGa)Se 2 thin films is hardly reported. In this paper, Cu(InGa)Se 2 thin films were prepared on quartz glass by e-beam evaporation via two-step process. Study of structural property showed that a certain amount of CaF 2 through post-deposition treatment was beneficial to the uniform composition distribution of Cu(InGa)Se 2 thin films. Near-surface region of Cu(InGa)Se 2 thin films was more Cu-depleted by increasing introduced amount of Ca element. It was inferred that Ca diffused into the Cu(InGa)Se 2 thin films substituted the In sites as Ca In so as to increase the carrier concentration. By calculation, the spike barrier of CdS/Cu(InGa)Se 2 heterojunction was shown to decrease with increased thickness of CaF 2 layers. As a result, Cu(InGa)Se 2 solar cell subjected to 20 nm CaF 2 post-deposition treatment, which possessed higher fill factor, open circuit voltage and short circuit current density, achieved the optimal power conversion efficiency. An efficiency of Cu(InGa)Se 2 solar cell was enhanced by 2.9% after 20 nm CaF 2 post-deposition treatment. Highlights • Well crystallized CIGS thin films were prepared on quartz glass via two-step process. • Ga graded distribution in the films was alleviated after CaF 2 PDT. • Near-surface region of CIGS thin films was more Cu-poor by increasing amount of Ca. • An efficiency of CIGS solar cell was enhanced by 2.9% through 20 nm CaF 2 PDT. [ABSTRACT FROM AUTHOR]

• CIGS solar cells were fabricated on ultrathin glass. • Potassium was doped by a simple method during the post-selenization process. • The efficiency of solar cell got enhanced by 2.5% after potassium incorporation. • It was first revealed that K doping retarded the property degradation of solar cell. Flexible Cu(InGa)Se 2 solar cells fabricated on metal foils and plastics have achieved high conversion efficiency so far. However, metal impurities and low temperature tolerance hinder them from further considerable development. Here, 150 μm-thick ultrathin glass with desirable advantages was applied as substrate for Cu(InGa)Se 2 solar cell. Potassium element was doped by a simple method during the post-selenization process. The results showed that the KInSe 2 phase existed in K-doped Cu(InGa)Se 2 films. The K-doped CIGS films were more compact than the pristine one due to the fact that K incorporated in films could form quasi-liquid alkali-metal-Se compounds and improve the compactness of films. K-incorporated CIGS films exhibited enhanced p-type conductivity and different surface energy level. Consequently, K-doped Cu(InGa)Se 2 solar cell achieved an optimal efficiency of 8.3%, which was relatively 43% higher than that of pristine solar cell. Investigation of performance and stability of solar cells manifested that the K incorporation retarded the performance degradation of device during cyclic bending. [ABSTRACT FROM AUTHOR]

• Cd-free CIGS solar cells with a-Si buffer layers are fabricated for the first time. • The conduction band alignment of CIGS/a-Si is a favorable spike. • SCAPS predicts enhanced efficiency by optimization of bandgap and E CB of CIGS films. • The efficiency of cell with modified CIGS film is relatively improved by over 30%. CdS, In 2 S 3 and ZnO-based materials are typically adopted as buffer layers in high efficiency CIGS solar cells. However, the drawbacks involved toxicity, complicated synthesis process and environmental damage of aforementioned materials would someday limit the development themselves. Here, for the first time, eco-friendly and low-cost a-Si thin films prepared by e-beam evaporation were used as buffer layers in CIGS solar cells. Thickness of a-Si films was changed to optimize the performance of CIGS solar cells through investigating their optical, structural and electrical properties. It revealed that the conduction band alignment of CIGS and a-Si is a favorable spike and a 60 nm a-Si film is optimal for CIGS/a-Si interface properties. Following the SCAPS simulation, bandgaps and conduction band energy level of CIGS films were facilely modulated through altering the Ga/(Ga + In) ratios. The conversion efficiency of solar cell with modified CIGS film was relatively improved by over 30% compared to the pristine one. The present work provides a new and eco-friendly strategy for fabrication of CIGS solar cells and expands the application of a-Si thin films as buffer layers for solar cells. [ABSTRACT FROM AUTHOR]