Hot Electron‐Based Solid State TiO₂|Ag Solar Cells

Abstract

plasmonic effect in the cells, and is not just supported or enhanced by it.The operation of plasmonic solar cells is dependent upon the optical excitation of surface plasmons, which are collective oscillations of the surface electronic cloud in metallic nanoparticles. One of the important characteristics of metallic nanoparticles is the coupling interaction of their plasmonic oscillations with incident photons of the same frequency; this coupling excites surface plasmon resonance (SPR). [ 1 ] The SPR gives rise to strong electromagnetic fi elds, which can be used for trapping or refl ecting light, enhancing photovoltaic activity, [ 2 ] surfaceenhanced Raman spectroscopy (SERS), [ 3 ] and photo-catalysis. [ 4 ] When the surface plasmon decays to the ground state it can cause electron excitation within the metallic nanoparticle itself, the excited electrons are often referred to as "hot" electrons. The "hot" electrons are highly active nonequilibrium electrons that have suffi cient kinetic energy to overcome potential barriers, or tunnel through thin layers of semiconductors. [ 5 ] Since the "hot" electrons are energetic they can be used in conjunction with a semiconductor, to form a Schottky barrier photovoltaic device. As the absorption and excitation of the SPR is very wide and extends beyond the visible range of the solar spectrum, depending on the material and structure, the "hot" electrons that are formed can extend the spectral response of the photovoltaic device. The "hot" electrons are directly injected into the conduction band of the semiconductor, forming and improving the photovoltaic activity.One of the semiconductors that is used extensively for renewable energy applications is TiO 2 , which is a wide bandgap (3.2 eV) metal oxide semiconductor. As it is a highly n-type material, it is utilized namely as an electron conducting layer in solar cells to help with charge separation, [ 6 ] or as a photocatalyst for water splitting. [ 7 ] The wide bandgap of the TiO 2 only allows it to be used for solar cells in conjunction with an absorbing material, be it dye, quantum dots, or other materials, since by itself it would only absorb light from the UV part of the solar spectrum. To improve or form the photovoltaic activity of the TiO 2 as an independent photovoltaic system, silver metallic nanoparticles or nanostructures can be used. The metallic nano particles form a Schottky barrier solar cell with the TiO 2 , and the "hot" electrons that have enough kinetic energy to overcome the Schottky barrier height are injected into the TiO 2 , asThe present work reports a simple and direct sputtering deposition to form solid state TiO 2 |Ag independent plasmonic solar cells. The independent plasmonic solar cells are based on a Schottky barrier between two materials, TiO 2 and Ag. The Ag functions as the absorber generating "hot" electrons, as well as the contact for the solar cell. The Ag sputtering is performed for different durations, to form Ag nanoparticles with a wide size distribution on the surface of rough sp...

How Transparent Oxides Gain Some Color: Discovery of a CeNiO3 Reduced Bandgap Phase As an Absorber for Photovoltaics

“…Together with the calculated bandgap ( E g ), of 1.6 eV for the CeNiO 3 and 3.28 eV for the TiO 2 , we were able to determine the energy positions of the materials, as can be seen in Figure a and b. The band positions show that the TiO 2 is a highly n-type material, which is to be expected for TiO 2 as the electron transport layer. The CeNiO 3 seems to be slightly p-type, which is beneficial for the solar cell activity as it will form a p-n heterojunction.…”

High‐Throughput Electrical Potential Depth‐Profiling in Air

“…Detailed band diagram of the FTO|TiO 2 |Co 3 O 4 structure. The ionization energy of Co 3 O 4 was measured using air‐photoemission and the band gaps of TiO 2 and Co 3 O 4 were determined from Tauc plots reported elsewhere . For the band diagram we used the 1.5 eV optical band gap for Co 3 O 4 .…”

Hot Electrons in TiO2–Noble Metal Nano-Heterojunctions: Fundamental Science and Applications in Photocatalysis

“…A very typical hot electron harvesting system consists of a TiO 2 –noble metal nanoparticle heterojunction. Au and Ag are the most common plasmonic noble metals utilized in plasmonic photocatalysis applications, while TiO 2 is a benchmark material for semiconductor-based photocatalysis [ 130 , 237 , 238 , 239 ]. In this section, we will briefly review hot electron phenomena in three categorical applications of photocatalytic technology: (i) photocatalytic degradation/aerobic oxidation of organic compounds, (ii) photocatalytic CO 2 reduction and H 2 generation, and (iii) photoelectrochemical water-splitting.…”

“…Apart from the electronic structure of the metal nanoparticle, numerous other properties, including the loading amount and size [ 151 ], architecture of the noble metal nanoparticle [ 58 , 60 , 181 , 238 ], the amplitude of UV irradiation [ 151 ], the structural distribution of the noble metal nanoparticle forming the semiconductor heterojunction (composite plasmonic nanostructure systems where the plasmonic noble metal is embedded within the semiconductor nanostructure as opposed to decorating the nanostructure have resulted in greater performance efficiencies), all influence the mechanism of hot electron injection in noble metal nanoparticle–semiconductor heterojunctions [ 195 , 249 , 289 ].…”