RESUMEN
This work reports on the properties of heterojunctions consisting of n-type Ga2O3 layers, deposited using ultrasonic spray pyrolysis at high temperature from water-based solution, combined with p-type NiO and Cu2O counterparts, deposited by radio frequency and reactive, direct-current magnetron sputtering, respectively. After a comprehensive investigation of the properties of the single layers, the fabricated junctions on indium tin oxide (ITO)-coated glass showed high rectification, with an open circuit voltage of 940 mV for Ga2O3/Cu2O and 220 mV for Ga2O3/NiO under simulated solar illumination. This demonstrates in praxis the favorable band alignment between the sprayed Ga2O3 and Cu2O, with small conduction band offset, and the large offsets anticipated for both energy bands in the case of Ga2O3/NiO. Large differences in the ideality factors between the two types of heterojunctions were observed, suggestive of distinctive properties of the heterointerface. Further, it is shown that the interface between the high-temperature-deposited Ga2O3 and the ITO contact does not impede electron transport, opening new possibilities for the design of solar cell and optoelectronic device architectures.
RESUMEN
A flexible transparent heater is presented, based on an all-sprayed composite architecture of indium-doped zinc oxide (IZO) layers that sandwich a network of silver nanowires, on a polyimide-foil substrate. This architecture could be materialized through the development of a low-temperature (240 °C) spray-pyrolysis process for the IZO layers, which is compatible with the thermal stability of the transparent polyimide substrate and allows for the formation of compact and transparent layers, without precipitates. The IZO layers entirely embed the silver nanowires, offering protection against environmental degradation and decreasing the junction resistance of the nanowire network. The resulting transparent heaters have a high mean transmittance of 0.76 (including the substrate) and sheet resistance of 7.5 Ω/sq. A steady-state temperature of ~130 °C is achieved at an applied bias of 3.5 V, with fast heater response times, with a time constant of ~4 s The heater is mechanically stable, reaching or surpassing 100 °C (at 3.5 V), under tensile, respectively, compressive-bending stress. This work shows that high-performance transparent heaters can be fabricated using all-sprayed oxide/silver-nanowire composite coatings, that are compatible with large-scale and low-cost production.
RESUMEN
The use of pre-synthesised Cu2ZnSnS4 (CZTS) sub-micron powders as a raw material for preparing CZTS thin films for photovoltaic absorber applications is examined. A challenge in preparing photovoltaic device-relevant CZTS films from submicron powders is producing a dense CZTS film by a sintering process. This is due to the nature of non-unimodal particle size and morphology that typically lead to the formation of pores after sintering. This work aimed to study the sintering behaviour of CZTS films that were prepared from a CZTS powder-containing ink. Complementary DT-TGA and in situ X-ray powder diffraction studies at elevated temperature reveal that the tetragonal kesterite phase in the as-sintered CZTS film is stable until 620 °C. An effective tendency of CZTS powder towards film recrystallisation occurs when alkali cations (Na and/or K) are added to the ink. For the first time, effects of additional natural gum as a binder in the CZTS powder-containing ink on the CZTS film sintering behaviour were also investigated. Contrary to the positive effects of alkali addition, the binder inhibits recrystallisation of CZTS. Therefore, the amount of binder was controlled in a quantity large enough to modify the ink viscosity, but low enough to allow large CZTS grain growth during sintering. A dense and compact as-sintered CZTS film can be produced from a CZTS powder-containing ink with 10 mol% Na and 2 mol% K alkali addition along with 3 wt% binder addition.