Charge transfer in photorechargeable composite films of TiO2 and polyaniline

A photorechargeable battery (PRB) is a photovoltaic device having an energy storage function in a single cell. The photoactive electrode of PRB is a bilayer film consisting of bare porous TiO2 and a TiO2-polyaniline (PANi) mixture that work as a photovoltaic current generator and an electrochemical energy storage by ion dedoping, respectively. To study the charge transfer between TiO2 and PANi, the photorechargeable quantum efficiency QE ([electron count on discharge]/[incident photon count on photocharge]) was measured by varying the thickness L-S of the TiO2-PANi mixture. The quantum efficiency QE(uv) for UV photons had a maximum of similar to 7% at L-S similar to 7 mu m. The time constant t(TP) for the charge transfer was about 10(-1) s, which was longer ten times or more than the lifetime of excited electrons within TiO2. These facts reveal that the main rate-limiting factor in the photocharging process is the charge transfer between TiO2 and PANi. (C) 2015 The Japan Society of Applied Physics