Growth of Hybrid Perovskites (HP) Light Harvesting Layer and TiO 2 Electron Transport Material for Solar Cells Application

Hybrid Perovskites (HP) recently emerged as alternative light harvesting layer to fabricate high efficiency thin film solar cells. The perovskite based solar cells took advantage of the experience gained in the field of the dye sensitizes solar cells and the extremely thin absorber (ETA) solar cells. It is worth mentioning that the structure of the perovskite solar cell is very similar to a dye sensitized solar cell and ETA solar cell. These cells are composed of the transparent conducting layer (TCO), the electron transport material (ETM) the absorber, the hole transport material, and the back contact. Our work focuses on the deposition and characterization of two components of the perovskite based solar cell. These components are the ETM which is titanium dioxide layer (TiO2) in this case and the absorber material which is the perovskite layer. Dip coating technique was used to grow compact and pinhole free TiO2 films from a solution of Titanium alkoxide diluted in isopropanol. The dip coating technique is particularly attractive for thin film solar cell application due to its simplicity, low cost, and good quality of films. For a compact film, dipping was restricted to two dips and four dips. The films were structurally and morphologically characterized by X-ray diffraction and scanning electron microscope (SEM). XRD analysis showed the deposited TiO2 films have anatase structure. SEM results showed a full coverage of the films with less pinholes. The two step sequential physical vapour deposition was performed to grow HP thin films using thermal evaporation technique. Thin films of HP were deposited using thermal evaporator under high vacuum from two sources namely lead iodide and methylamine iodide. Firstly, Lead iodide was deposited which acts as a template for the crystallization of perovskite layers. Then methylamine iodide was deposited for the desired film. X-ray diffraction of the as deposited film showed the presence of mixed phases of lead iodide and perovskites. This indicates at room temperature methylamine iodide diffused deep enough in the lead iodide film to form the perovskite structure. Films were then annealed at 110 °C for 1 hour in nitrogen atmosphere for better crystallinity which is proven by the sharper and high pick intensities. Also, varying the ratio of both organic and inorganic sources did not influence the presence of lead iodide phases as confirmed by XRD. Further optimization are in progress to form single perovskite phase formation.