Optimization of Fabrication Processes of Non Halide Pb Precursor Based Perovskite Solar Cells

Abstract

The organic-inorganic halide perovskite solar cells have continued to attract serious research interest since the first introduction as solar light absorber by Miyasaka and co-workers with a power conversion efficiency (PCE) of 3.8% in 2009 to the current value of over 25.2%. This outcome is due to the tremendous advantages of the perovskite materials ( e.g., as the tunable bandgap, direct bandgap, large optical absorption coefficient, high charge carrier mobilities, low exciton binding energy, and cost-effective solution process-able). Despite the successes recorded so far on lead halide perovskite solar cells the problem of toxicity and stability is still unresolved. In this thesis, novel approaches were used to optimised the fabrication processes of perovskite solar cells obtained from dehydrated lead acetate as source materials in other to improve efficiency and stability. The impact of solution concentration on the photovoltaic and the material properties of perovskite solar cells (PSCs) obtained from dehydrated Pb-acetate precursors was investigated. The optimal solution concentration was found to be 1.0 M which provide the best efficiency. Reproducibility is also an important problem in perovskite solar cells fabrication processes. In this study, we reported a low-temperature, one-step solution process to fabricate perovskite solar cells. These perovskite films were aged at 200 sec before thermal annealing at 90 oC for 5 min. Uniform perovskite films with fewer pinholes were obtained by this technique. The inverted planar (n-i-p) perovskite solar cell device resulted in a power conversion efficiency of 13%. A substantial finding was that the devices demonstrated high reproducibility. We also investigated the effect of annealing temperature on the optical and structural properties of the films and the photovoltaic performances of the fabricated solar cell devices. For the aforementioned process, a low-temperature, one-step solution process, the optimal temperature was achieved at 90 oC. In another study, the role of hafnium acetylacetonate buffer on the performance and stability of perovskite solar cells were investigated. The optimum concentration of the Hfaca was found to be 1.0 mg/ml resulting in power conversion efficiency (PCE) of 12.23% corresponding to over 30% improvement when compared to the control device (PCBM/Ag) without Hfaca which has a PCE of 8.89%. Hfaca as a buffer layer leads to superior stability retaining about 90% of its original values of the PCE after 15 days of storage in the glove box compared to the control device which retains 70% of the initial PCE value under the same storage.