Thin Film Co₃O₄/TiO₂ Heterojunction Solar Cells

Abstract

Co 3 O 4 is investigated as a light absorber for all‐oxide thin‐film photovoltaic cells because of its nearly ideal optical bandgap of around 1.5 eV. Thin film TiO 2 /Co 3 O 4 heterojunctions are produced by spray pyrolysis of TiO 2 as a window layer, followed by pulsed laser deposition of Co 3 O 4 as a light absorbing layer. The photovoltaic performance is investigated as a function of the Co 3 O 4 deposition temperature and a direct correlation is found. The deposition temperature seems to affect both the crystallinity and the morphology of the absorber, which affects device performance. A maximum power of 22.7 μW cm −2 is obtained at the highest deposition temperature (600 °C) with an open circuit photovoltage of 430 mV and a short circuit photocurrent density of 0.2 mA cm −2 . Performing deposition at 600 °C instead of room temperature improves power by an order of magnitude and reduces the tail states (Urbach edge energy). These phenomena can be explained by larger grains that grows at high temperature, as opposed to many nucleation events that occur at lower temperature.