From Copper Zinc Tin Sulfur to Perovskites: Fabrication and Characterization of New Generation of Solar Cells

In 2013, the worldwide production of renewable electricity accounted for 22.1% of the total energy production with 0.9% coming from solar photovoltaics (PVs). Recently, there has been a growing interest for Cu2ZnSnS4 (CZTS) quaternary semiconductor due to the abundance and low cost of its precursors. Moreover, this chalcopyrite material has an ideal direct band gap around 1.5 eV, high absorption coefficient (α \u3e104 cm-1) and high conductivity, making it suitable for nanostructured and dye-sensitized solar cell (DSSC) applications. Here, CZTS nanoparticles have been synthesized by pulsed laser deposition (PLD) and simultaneously deposited in the interstitial space of ZnO nanowire arrays to form bulk heterojunction 3D nanostructured solar cells. Secondly, vertically oriented CZTS nanoplates have been synthesized by PLD and used as counter electrode in platinum-free dye-sensitized solar cells. These CZTS nanostructures proved to be suitable in achieving workable solar cells, which could significantly cut down the cell cost and provide environmentally friendly photovoltaic devices. Alternately, hybrid organic–inorganic perovskite solar cells have become one of the most attractive photovoltaic technologies with easy solution fabrication and high conversion efficiencies. However, the devices remain unstable under certain processing and environmental conditions. Herein, formamidinium lead tri-halide perovskite (FAPbI3) planar heterojunction solar cells have been fabricated under a controlled environment. The fabrication parameters (precursor concentration, annealing, etc) and the effect of humidity on the structural, optical, and electrical properties of FAPbI3 thin films and devices have been investigated and proved to be critical in the processing of efficient devices. Solar cells with conversion efficiency of 16.6% have been obtained. Furthermore, in-situ techniques such as in-situ (scanning) transmission electron microscopy and in-situ XRD were performed to understand the crystallization and degradation mechanisms of FAPbI3 thin films.The in-situ data were correlated with planar heterojunction FAPbI3 devices efficiency data in order to improve the device fabrication process

From Copper Zinc Tin Sulfur to Perovskites: Fabrication and Characterization of New Generation of Solar Cells

In 2013, the worldwide production of renewable electricity accounted for 22.1% of the total energy production with 0.9% coming from solar photovoltaics (PVs). Recently, there has been a growing interest for Cu2ZnSnS4 (CZTS) quaternary semiconductor due to the abundance and low cost of its precursors. Moreover, this chalcopyrite material has an ideal direct band gap around 1.5 eV, high absorption coefficient (α \u3e104 cm-1) and high conductivity, making it suitable for nanostructured and dye-sensitized solar cell (DSSC) applications. Here, CZTS nanoparticles have been synthesized by pulsed laser deposition (PLD) and simultaneously deposited in the interstitial space of ZnO nanowire arrays to form bulk heterojunction 3D nanostructured solar cells. Secondly, vertically oriented CZTS nanoplates have been synthesized by PLD and used as counter electrode in platinum-free dye-sensitized solar cells. These CZTS nanostructures proved to be suitable in achieving workable solar cells, which could significantly cut down the cell cost and provide environmentally friendly photovoltaic devices. Alternately, hybrid organic–inorganic perovskite solar cells have become one of the most attractive photovoltaic technologies with easy solution fabrication and high conversion efficiencies. However, the devices remain unstable under certain processing and environmental conditions. Herein, formamidinium lead tri-halide perovskite (FAPbI3) planar heterojunction solar cells have been fabricated under a controlled environment. The fabrication parameters (precursor concentration, annealing, etc) and the effect of humidity on the structural, optical, and electrical properties of FAPbI3 thin films and devices have been investigated and proved to be critical in the processing of efficient devices. Solar cells with conversion efficiency of 16.6% have been obtained. Furthermore, in-situ techniques such as in-situ (scanning) transmission electron microscopy and in-situ XRD were performed to understand the crystallization and degradation mechanisms of FAPbI3 thin films.The in-situ data were correlated with planar heterojunction FAPbI3 devices efficiency data in order to improve the device fabrication process

Towards One Key to One Lock: Catalyst Modified Indium Oxide Nanoparticle Thin Film Sensor Array for Selective Gas Detection

Homogeneous In2O3 nanoparticles (NPs) were self-assembled into thin film sensor arrays on a single chip, with further surface modification by noble metal catalysts. The NP film sensor arrays show clear current responses when exposed to different target gases, and both sensitivity and selectivity were greatly improved. Particularly, the sensors modified with Au, Pd, and Pt nanocatalysts demonstrated higher sensitivity to H2S, H-2 and CO, respectively, making the gas discrimination direct and simple, like one key to one lock . The particle size dependence of the noble metal modifiers to the sensitivity was further investigated by tuning the sputtering parameters. Three different trends of sensitivities were observed, each attributed to different mechanisms. The modified nanoparticle film sensor was also fabricated on flexible substrates and the sensing performance was investigated at different bending angles

Towards One Key to One Lock: Catalyst Modified Indium Oxide Nanoparticle Thin Film Sensor Array for Selective Gas Detection

Homogeneous In2O3 nanoparticles (NPs) were self-assembled into thin film sensor arrays on a single chip, with further surface modification by noble metal catalysts. The NP film sensor arrays show clear current responses when exposed to different target gases, and both sensitivity and selectivity were greatly improved. Particularly, the sensors modified with Au, Pd, and Pt nanocatalysts demonstrated higher sensitivity to H2S, H-2 and CO, respectively, making the gas discrimination direct and simple, like one key to one lock . The particle size dependence of the noble metal modifiers to the sensitivity was further investigated by tuning the sputtering parameters. Three different trends of sensitivities were observed, each attributed to different mechanisms. The modified nanoparticle film sensor was also fabricated on flexible substrates and the sensing performance was investigated at different bending angles

Investigating the Surface Modification of In2O3 Nanocrystals for Enhanced Chemical Sensing

In2O3, with a wide-band gap (3.6 eV), is an n-type semiconductive material, which has been extensively studied in the field of chemical sensors. Pt deposition on metal oxide gas sensors was found to increase the sensitivity of the device towards specific gases. Our work focuses on comparing the effects of physical and chemical methods of Pt deposition on In2O3 nanocrystal thin films, on the sensitivity of the fabricated chemical sensors. A one-step synthesis was used to attach the Pt nanoparticles on the In2O3 nanocrystals. Devices fabricated using unmodified, physically modified, and chemically modified In2O3 were compared under H2S atmosphere

Effect of Water Vapor, Temperature, and Rapid Annealing on Formamidinium Lead Triiodide Perovskite Crystallization

Perovskite-based solar cells are one of the emerging candidates for radically lower cost photovoltaics. Herein, we report on the synthesis and crystallization of organic–inorganic formamidinium lead triiodide perovskite films under controlled atmospheric and environmental conditions. Using in situ (scanning) transmission electron microscopy, we make observations of the crystallization process of these materials in nitrogen and oxygen gas with and without the presence of water vapor. Complementary planar samples were also fabricated in the presence of water vapor and characterized by in situ X-ray diffraction. Direct observations of the material structure and final morphology indicate that the exposure to water vapor results in a porous film that is metastable, regardless of the presence of argon, nitrogen, or oxygen. However, the optimal crystallization temperature of 175 °C is unperturbed across conditions. Rapid modulation about the annealing temperature of 175 °C in ±25 °C steps (150–200 °C) promotes crystallization and significantly improves the film morphology by overcoming the presence of impregnated water trapped in the material. Following this processing protocol, we demonstrate substantial growth to micron-size grains via observation inside of an environmentally controlled transmission electron microscope. Adapting this insight from our in situ microscopy, we are able to provide an informed materials protocol to control the structure and morphology of these organic–inorganic semiconductors, which is readily applicable to benchtop device growth strategies

Mechanisms of Electron-Beam-Induced Damage in Perovskite Thin Films Revealed by Cathodoluminescence Spectroscopy

Electron-beam-induced damages in methylammonium lead triiodide (MAPbI₃) perovskite thin films were studied by cathodo­luminescence (CL) spectroscopy. We find that high-energy electron beams can significantly alter perovskite properties through two distinct mechanisms: (1) defect formation caused by irradiation damage and (2) phase transformation induced by electron-beam heating. The former mechanism causes quenching and broadening of the excitonic peaks in CL spectra, whereas the latter results in new peaks with higher emission photon energy. The electron-beam damage strongly depends on the electron-beam irradiation conditions. Although CL is a powerful technique for investigating the electronic properties of perovskite materials, irradiation conditions should be carefully controlled to avoid any significant beam damage. In general, reducing acceleration voltage and probing current, coupled with low-temperature cooling, is more favorable for CL characterization and potentially for other scanning electron-beam-based techniques as well. We have also shown that the stability of perovskite materials under electron-beam irradiation can be improved by reducing defects in the original thin films. In addition, we investigated effects of electron-beam irradiation on formamidinium lead triiodide (FAPbI₃) and CsPbI₃ thin films. FAPbI₃ shows similar behavior as MAPbI₃, whereas CsPbI₃ displays higher resistance to electron-beam damage than its organic–inorganic hybrid counterparts. Using CsPbI₃ as a model material, we observed nonuniform luminescence in different grains of perovskite thin films. We also discovered that black-to-yellow phase transformation of CsPbI₃ tends to start from the junctions at grain boundaries