Search Results (8)

This study successfully fabricated the quaternary topological insulator thin films of Bi_1.2Sb_0.8Te_0.4Se_2.6 (BSTS) with a thickness of 25 nm, improving the intrinsic defects in binary topological materials through doping methods and achieving the separation of transport characteristics between the bulk and surface of topological insulator materials by utilizing a comprehensive Physical Properties Measurement System (PPMS) and Terahertz Time-Domain Spectroscopy (THz-TDS) to extract electronic transport information for both bulk and surface states. Additionally, the dielectric polarization behavior of BSTS in the low-frequency (10–10⁷ Hz) and high-frequency (0.5–2.0 THz) ranges was investigated. These research findings provide crucial experimental groundwork and theoretical guidance for the development of novel low-energy electronic devices, spintronic devices, and quantum computing technology based on topological insulators. Full article

Thin-film solar cells have been referred to as second-generation solar photovoltaics (PV) or next-generation solutions for the renewable energy industry. The layer of absorber materials used to produce thin-film cells can vary in thickness, from nanometers to a few micrometers. This is much thinner than conventional solar cells. This review focuses on inorganic thin films and, therefore, hybrid inorganic–organic perovskite, organic solar cells, etc., are excluded from the discussion. Two main families of thin-film solar cells, i.e., silicon-based thin films (amorphous (a-Si) and micromorph silicon (a-Si/c-Si), and non-silicon-based thin films (cadmium telluride (CdTe) and copper–indium–gallium diselenide (CIGS)), are being deployed on a commercial scale. These commercial technologies, until a few years ago, had lower efficiency values compared to first-generation solar PV. In this regard, the concept of driving enhanced performance is to employ low/high-work-function metal compounds to form asymmetric electron and hole heterocontacts. Moreover, there are many emerging thin-film solar cells conceived to overcome the issue of using non-abundant metals such as indium (In), gallium (Ga), and tellurium (Te), which are components of the two commercial thin-film technologies, and therefore to reduce the cost-effectiveness of mass production. Among these emerging technologies are kesterite CZTSSE, intensively investigated as an alternative to CIGS, and Sb₂(S,Se)₃. In this review, after a general overview of the current scenario of PV, the three main challenges of inorganic thin-film solar cells, i.e., the availability of (safe) metals, power conversion efficiency (PCE), and long-term stability, are discussed. Full article

Antimony selenide (Sb₂Se₃) is emerging as a promising photovoltaic material owing to its excellent photoelectric property. However, the low carrier transport efficiency, and detrimental surface oxidation of the Sb₂Se₃ thin film greatly influenced the further improvement of the device efficiency. In this study, the introduction of tellurium (Te) can induce the benign growth orientation and the desirable Sb/Se atomic ratio in the Te-Sb₂Se₃ thin film. Under various characterizations, it found that the Te-doping tended to form Sb₂Te₃-doped Sb₂Se₃, instead of alloy-type Sb₂(Se,Te)₃. After Te doping, the mitigation of surface oxidation has been confirmed by the Raman spectra. High-quality Te-Sb₂Se₃ thin films with preferred [hk1] orientation, large grain size, and low defect density can be successfully prepared. Consequently, a 7.61% efficiency Sb₂Se₃ solar cell has been achieved with a V_OC of 474 mV, a J_SC of 25.88 mA/cm², and an FF of 64.09%. This work can provide an effective strategy for optimizing the physical properties of the Sb₂Se₃ absorber, and therefore the further efficiency improvement of the Sb₂Se₃ solar cells. Full article

Bismuth telluride-based thin films have been investigated as the active material in flexible and micro thermoelectric generators (TEGs) for near room-temperature energy harvesting applications. The latter is a class of compact printed circuit board compatible devices conceptualized for operation at low-temperature gradients to generate power for wireless sensor nodes (WSNs), the fundamental units of the Internet-of-Things (IoT). CMOS and MEMS compatible micro-TEGs require thin films that can be integrated into the fabrication flow without compromising their thermoelectric properties. We present results on the thermoelectric properties of (Bi,Sb)₂(Se,Te)₃ thin films deposited via thermal evaporation of ternary compound pellets on four-inch SiO₂ substrates at room temperature. Thin-film compositions and post-deposition annealing parameters are optimized to achieve power factors of 2.75 mW m⁻¹ K⁻² and 0.59 mW m⁻¹ K⁻² for p-type and n-type thin films. The measurement setup is optimized to characterize the thin-film properties accurately. Thin-film adhesion is further tested and optimized on several substrates. Successful lift-off of p-type and n-type thin films is completed on the same wafer to create thermocouple patterns as per the target device design proving compatibility with the standard MEMS fabrication process. Full article

Thin-film solar cells are simple and affordable to produce, but their efficiency is low compared to crystalline-silicon solar cells, and needs to be improved. This study investigates the photovoltaic performance of different absorber materials (CdTe, CIGS, Sb₂Se_3, and CZTS) with simple structure Au/absorber/CdS/ITO. The research uses the SCAPS (Solar Cell Capacitance Simulator), a mathematical model based on Poisson and continuity equations. The impact of various parameters on cell performance, such as absorber layer thickness, acceptor density, electron affinity, back contact work function, and temperature, are examined. As per the simulation results, an absorber thickness of 4 µm is suitable for achieving the maximum efficiency for all the absorber materials. The optimized acceptor density for CdTe/CIGS/ Sb₂Se₃ and CZTS is taken as 10¹⁶ cm⁻³ and 10¹⁷ cm⁻³, respectively. The back contact work function and device temperature were set to be 5.1 eV and 300 K, respectively, to achieve excellent performance. Among all the absorber materials, the highest efficiency of 28.2% was achieved for CZTS. The aim is to highlight the various absorber layers’ performances by optimizing the device parameters. The obtained results can be used in solar energy harvesting applications due to the improved performance characteristics. Full article

In this study, the efficient generation of terahertz radiation by a dipole photoconductive antenna, based on a thin island film of a topological insulator, was experimentally demonstrated. The performance of the Bi_1.9Sb_0.1Te₂Se antenna was shown to be no worse than those of a semiconductor photoconductive antenna, which is an order of magnitude thicker. The current–voltage characteristics were studied for the photo and dark currents in Bi_1.9Sb_0.1Te₂Se. The possible mechanisms for generating terahertz waves were analyzed by comparing the characteristics of terahertz radiation of an electrically biased and unbiased topological insulator. Full article

Antimony selenide (Sb₂Se₃) has been widely investigated as a promising absorber material for photovoltaic devices. However, low open-circuit voltage (V_oc) limits the power conversion efficiency (PCE) of Sb₂Se₃-based cells, largely due to the low-charge carrier density. Herein, high-quality n-type (Tellurium) Te-doped Sb₂Se₃ thin films were successfully prepared using a homemade target via magnetron sputtering. The Te atoms were expected to be inserted in the spacing of (Sb₄Se₆)_n ribbons based on increased lattice parameters in this study. Moreover, the thin film was found to possess a narrow and direct band gap of approximately 1.27 eV, appropriate for harvesting the solar energy. It was found that the photoelectric performance is related to not only the quality of films but also the preferred growth orientation. The Te-Sb₂Se₃ film annealed at 325 °C showed a maximum photocurrent density of 1.91 mA/cm² with a light intensity of 10.5 mW/cm² at a bias of 1.4 V. The fast response and recovery speed confirms the great potential of these films as excellent photodetectors. Full article

Recently, Kayyalha et al. (Phys. Rev. Lett., 2019, 122, 047003) reported on the anomalous enhancement of the self-field critical currents (I_c(sf,T)) at low temperatures in Nb/BiSbTeSe₂-nanoribbon/Nb Josephson junctions. The enhancement was attributed to the low-energy Andreev-bound states arising from the winding of the electronic wave function around the circumference of the topological insulator BiSbTeSe₂ nanoribbon. It should be noted that identical enhancement in I_c(sf,T) and in the upper critical field (B_c2(T)) in approximately the same reduced temperatures, were reported by several research groups in atomically thin junctions based on a variety of Dirac-cone materials (DCM) earlier. The analysis shows that in all these S/DCM/S systems, the enhancement is due to a new superconducting band opening. Taking into account that several intrinsic superconductors also exhibit the effect of new superconducting band(s) opening when sample thickness becomes thinner than the out-of-plane coherence length (ξ_c(0)), we reaffirm our previous proposal that there is a new phenomenon of additional superconducting band(s) opening in atomically thin films. Full article