Abstract
Rutile-phase TiO2 nanoparticles are embedded within an organic SiO2 matrix (Spin-On Glass) and the final suspension is deposited by spinning on (a) thin aluminum stripes or (b) in between thin aluminum films and ultra-thin titanium stripes. The maximum processing temperature for both devices is 220 � C. The first device is a “horizontal” TiO2:SiO2/Al/Glass photoactive structure which is then electrically characterized under dark and illuminated conditions (I–V -Light) so that the total resistance of a simple aluminum stripe is measured before/after ultraviolet-visible (UV-Vis) irradiation. Compared to dark conditions, excess carriers are photogenerated within the TiO2 nanoparticles during light exposure and they are transferred to both ends of the aluminum stripe after applying a low potential difference. A large decrease in the resistance of the aluminum stripe (down to 43% of its original value) is obtained when this horizontal structure is irradiated with UV-B light thus acting as a photoresistor. The second device is a “vertical” Ti/TiO2:SiO2/Al/Glass photoactive structure. Here, the path for photogenerated and electrically-driven carriers occurs vertically, or inside a Metal-Insulator-Metal (MIM) capacitor. Because of the ultra-thin titanium layer (100 A in thickness), this gate electrode is highly transparent to most of the UV-Vis irradiation so that when all carriers are being photogenerated, they are almost immediately separated at the top/bottom electrodes by a small applied electric field due to the thin and high-dielectric constant of the photoactive TiO2:SiO2 film. This way, a fast and large increase/decrease in gate current (about 4–7 orders of magnitude) is observed when this device is under illumination/dark conditions. This vertical structure operates as a photocapacitor, where all photogenerated carriers could be efficiently stored within the MIM capacitor itself and thus, enable simultaneous conversion and storage of solar energy in the same device.
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