Combinatorial Chemical Bath Deposition of CdS Contacts for Chalcogenide Photovoltaics

Structural and optical properties of amorphous Si-Ge-Te thin films prepared by combinatorial sputtering

The lack of order in amorphous chalcogenides offers them novel properties but also adds increased challenges in the discovery and design of advanced functional materials. The amorphous compositions in the Si–Ge–Te system are of interest for many applications such as optical data storage, optical sensors and Ovonic threshold switches. But an extended exploration of this system is still missing. In this study, magnetron co-sputtering is used for the combinatorial synthesis of thin film libraries, outside the glass formation domain. Compositional, structural and optical properties are investigated and discussed in the framework of topological constraint theory. The materials in the library are classified as stressed-rigid amorphous networks. The bandgap is heavily influenced by the Te content while the near-IR refractive index dependence on Ge concentration shows a minimum, which could be exploited in applications. A transition from a disordered to a more ordered amorphous network at 60 at% Te, is observed. The thermal stability study shows that the formed crystalline phases are dictated by the concentration of Ge and Te. New amorphous compositions in the Si–Ge–Te system were found and their properties explored, thus enabling an informed and rapid material selection and design for applications.

An Inter-Laboratory Study of Zn-Sn-Ti-O Thin Films using High-Throughput Experimental Methods

High-throughput experimental (HTE) techniques are an increasingly important way to accelerate the rate of materials research and development for many technological applications. However, there are very few publications on the reproducibility of the HTE results obtained across different laboratories for the same materials system, and on the associated sample and data exchange standards. Here, we report a comparative study of Zn-Sn-Ti-O thin films materials using high-throughput experimental methods at National Institute of Standards and Technology (NIST) and National Renewable Energy Laboratory (NREL). The thin film sample libraries were synthesized by combinatorial physical vapor deposition (cosputtering and pulsed laser deposition) and characterized by spatially resolved techniques for composition, structure, thickness, optical, and electrical properties. The results of this study indicate that all these measurement techniques performed at two different laboratories show excellent qualitative agreement. The quantitative similarities and differences vary by measurement type, with 95% confidence interval of 0.1-0.2 eV for the band gap, 24-29 nm for film thickness, and 0.08 to 0.37 orders of magnitude for sheet resistance. Overall, this work serves as a case study for the feasibility of a High-Throughput Experimental Materials Collaboratory (HTE-MC) by demonstrating the exchange of high-throughput sample libraries, workflows, and data.

Chemically Deposited CdS Buffer/Kesterite Cu2ZnSnS4 Solar Cells: Relationship between CdS Thickness and Device Performance

Earth-abundant, copper-zinc-tin-sulfide (CZTS), kesterite, is an attractive absorber material for thin-film solar cells (TFSCs). However, the open-circuit voltage deficit (V_oc-deficit) resulting from a high recombination rate at the buffer/absorber interface is one of the major challenges that must be overcome to improve the performance of kesterite-based TFSCs. In this paper, we demonstrate the relationship between device parameters and performances for chemically deposited CdS buffer/CZTS-based heterojunction TFSCs as a function of buffer layer thickness, which could change the CdS/CZTS interface conditions such as conduction band or valence band offsets, to gain deeper insight and understanding about the V_oc-deficit behavior from a high recombination rate at the CdS buffer/kesterite interface. Experimental results show that device parameters and performances are strongly dependent on the CdS buffer thickness. We postulate two meaningful consequences: (i) Device parameters were improved up to a CdS buffer thickness of 70 nm, whereas they deteriorated at a thicker CdS buffer layer. The V_oc-deficit in the solar cells improved up to a CdS buffer thickness of 92 nm and then deteriorated at a thicker CdS buffer layer. (ii) The minimum values of the device parameters were obtained at 70 nm CdS thickness in the CZTS TFSCs. Finally, the highest conversion efficiency of 8.77% (V_oc: 494 mV, J_sc: 34.54 mA/cm², and FF: 51%) is obtained by applying a 70 nm thick CdS buffer to the Cu₂ZnSn(S,Se)₄ absorber layer.

Solubility limits in quaternary SnTe-based alloys

A combined theoretical and experimental approach was used to determine the equilibrium as well as non-equilibrium solubility lines in the quaternary Sn_1−yMn_yTe_1−xSe_x alloy space, revealing a large area of accessible metastable phase space.