Developing Novel HTM Thin Films for Hybrid Perovskite Photovoltaics

Abstract

With an increase of global energy consumption, utilizing sustainable energy sources such as solar energy has attracted significant research interest. Solar energy can be converted into electrical energy using photovoltaic cells. Silicon photovoltaic cells have been dominating the market. However, the production of these photovoltaic cells requires both high temperatures and high purity materials. A potentially cheaper and more efficient alternative to silicon photovoltaic cells is the thin film hybrid perovskite, MAPbI3, photovoltaic cell. However, to make the MAPbI3 photovoltaic cells competitive with silicon photovoltaic cells, the efficiency and long term stability have to be increased further as well as a reduction of the material costs. One approach to achieve this is to replace the expensive organic hole transport materials used in MAPbI3 photovoltaic cells with transition metal oxides. Within this research, undoped and 0.1-to-10 mol% Co2+ doped NiO as well as undoped Co3O4 thin films have been prepared on both FTO and glass substrates to act as hole transport materials for MAPbI3 photovoltaic cells. These metal oxide thin films were coated uniformly on FTO whereas a partial coating on glass was observed. The effect of Co2+ dopant was observed with an increase of the unit cell parameter of the NiO cubic crystal lattice as well as an increase in the crystallite size going from respectively 4.639 Å and 173 Å for undoped NiO to 4.668 Å and 254 Å for 10 mol% Co doped NiO. An increase on the photoluminescence quenching of MAPbI3 from 14.7% for undoped NiO to 90.8% for 10 mol% Co doped NiO and 98.8% for Co3O4 was observed. The MAPbI3 photovoltaic cells achieved low photon-to-current efficiencies of 0.25% due to rapid decomposition of MAPbI3 upon sputtering of a silver cathode layer as observed with XRD.