Kuei-Hsien Chen

Tin monosulfide (SnS) is a promising light-harvesting material for solar cell applications, owing to its potential for large-scale production, cost-effectiveness, eco-friendly source materials, and long-term stability. However, SnS crystallizes in an orthorhombic structure, which results in a highly anisotropic charge transport behavior. Tailoring the crystallographic orientation of the SnS absorber layer plays a critical role in the enhancement of the transfer of charge carriers and the power conversion efficiency (PCE). By controlling the substrate tilting angle and temperature ramp rate in vapor transport deposition, the crystal growth orientation was tuned to a preferred direction which significantly suppressed the unfavorable (040) crystallographic plane. Through the combination of these two approaches, the PCE could be increased from 0.11% to 2%. The effect of the tilting angle was numerically simulated to investigate its role in controlling the film uniformity and directing the film growth. In addition, the correlation between the texture coefficient of the (040) plane and the charge transport properties was determined by a combination of analytical methods such as device performance studies, electrochemical impedance spectroscopy, along with transient photovoltage, space-charge-limited current, and dark current measurements. These techniques were blended together to prove that the marked improvement in PCE can be ascribed to a reduced charge recombination (in both SnS bulk and interfaces) and an enhanced hole mobility.

Bi doped Mg2Si0.4Sn0.6 had been synthesised in a high energy ball mill followed by compaction using a sintering hot press. The structural and compositional characterization of sintered mass indicated the formation of a highly densified single-phase product. The microstructure of the hot-pressed samples had been critically assessed. Thermoelectric properties were measured between room temperature and 723 K. A decrease in electrical conductivity was found with the increase in temperature but the Seebeck coefficient showed a reverse trend justifying the attainment of degenerate semiconducting behaviour. Meanwhile, the lattice thermal conductivity was subdued to 1.5 W/mK at 623 K. However, the highest zT value of 0.8 was achieved at 723 K. Moreover, the detailed X-ray photoelectron spectroscopic analysis was carried for the determination of binding energy of the constituent elements in the experimental alloy; it also provided the correct estimation of atomic percentage of the concerned elements. The Raman spectrum revealed a shift in F2g peak with respect to that of Mg2Sn and Mg2Si in correspondence with the composition of the synthesised alloy. The synthesised alloy showed micro and nano hardness of 3.7 and 4.03 GPa respectively, which implies that good mechanical strength could be achieved in the synthesised alloy.