Annealing effect of E-beam evaporated TiO2 films and their performance in perovskite solar cells

Abstract

Titanium dioxide (TiO2) films have been deposited on indium-doped tin oxide (ITO) glass substrate by electron-beam evaporation (EBE) system at room temperature (RT, 25 °C). After that, prepared TiO2 films are annealed at different temperatures of 150, 250, 350, 400, 450 and 500 °C. The novelty of this work is to investigate the effect of annealing temperature on the photovoltaic performances of perovskite solar cell (PeSC) with these annealed TiO2/ITO structures. For the fabrication of PeSC, perovskite (PRV) layer has been fabricated on TiO2 films by two-steps method. The TiO2 film prepared at RT shows the amorphous structure with the compact surface and Ti3+ state. Interestingly, crystallinity and porosity of the TiO2 films increase with the increase of annealing temperature. The TiO2 films annealed at 500 °C have shown high crystallinity with Ti4+ state and mixed phases (anatase and rutile). The grain boundary becomes visible, the size and porosity of TiO2 films increase with the increase of annealing temperature. The PeSC with TiO2 films prepared at RT shows the highest photoelectric conversion efficiency (PCE) of 6.15% with maximum photocurrent (14.37 mA/cm2) than the other PeSCs with annealed TiO2 films. The PCE, photocurrent and fill factor of PeSC decrease but the photovoltage increases with increase in annealing temperature, which may be caused by carrier leakage between PRV layer and ITO substrate, high series and low shunt resistances, and also the enhanced sheet resistance of ITO substrate.