DIRECT FORMATION OF HOT ELECTRON BASED SOLID STATE TiO₂|Ag PHOTOVOLTAICS

TiO₂, a photoactive semiconductor (E_g= 3.2 eV), cannot generate enough current to sustain power in a photovoltaic device due to its limited UV spectral activity. Recently, it was shown that plasmonic nanoparticles can inject hot electrons into TiO₂ and extend the photovoltaic spectral response. However, in order to obtain these nanoparticles in a homogeneous and organized way, their formation requires patterning or special preparation techniques.

Using a combinatorial investigation we show that hot electron generation can occur in Ag nanostructures formed on TiO₂ using sputtering. We prepared a solid state plasmonic solar cell, based on TiO₂ and Ag, using direct deposition techniques and with no hole-transport material. To obtain these solar cells, silver was deposited with different thicknesses by sputtering. The silver nanostructures are formed by the rough nature of the TiO_2, which was prepared by spray pyrolysis. The Ag has a dual role both as the current conductor and as the metal forming a Schottky barrier with the TiO₂. The Ag generates hot electrons upon illumination that are injected into the TiO₂, enhancing the photovoltaic activity of the solar cells into the visible region of the solar spectrum.

We provide evidence for the plasmonic photovoltaic activity by carrying out IPCE measurements that show a current onset at around 700 nm, while XPS results reveal a wide spread plasmonic peak for the Ag. I-V measurements show photovoltaic activity dependent on the Ag back contact thickness. The best cell performances give short circuit currents up to 1.18 mA cm^-2 and open circuit voltages up to 380 mV. To our knowledge the obtained currents are much higher than any previous report for TiO₂/Ag solar cells.