Development of Efficient and Stable Perovskite Solar Cells with Composition and Interface Engineering

Organic-inorganic hybrid perovskites (OIHPs) have drawn tremendous research attention in the past years because of their various advantages for photovoltaic applications such as large absorption coefficient, suitable bandgap, excellent crystallinity and long carrier diffusion length. To judge the feasibility of commercialization of a photovoltaic technology, three factors are usually considered: cost, efficiency and stability. Perovskite solar cells are predicted to be low-cost because of its low material and fabrication costs, while the efficiency and stability still require further development. This dissertation focused on the efficiency and operation stability enhancement of OIHP solar cell by controlling the OIHP film fabrication process, interfacial layers, passivation techniques and compositional manipulation. In Chapter 2, the morphology of methylammonium lead iodide (MAPbI3) perovskite films fabricated by one-step method was studied and improved by adopting a non-stoichiometry precursor ratio. By using a unique double fullerene layer structure to passivate the trap states, devices with a high fill factor of 80.1% were achieved for perovskite solar cells under one sun illumination. In Chapter 3, a doped hole transporting polymer was used in MAPbI3 perovskite solar cells to further improve perovskite efficiency to 17.5%. Doping the transporting layer reduce device series resistance to increase device fill factor and open circuit voltage without sacrificing the short circuit current. In Chapter 4, a tunneling contact was used on top of MAPbI3 layers to increase the efficiency of perovskite solar cells to 20.3%. The tunneling layers made of hydrophobic polymers also significantly enhance the stability of perovskite solar cells in humid air. In Chapter 5, another promising inorganic perovskite material, cesium lead iodide (CsPbI3), was used improve the thermal stability of perovskite solar cells. Sulfobetaine zwitterion was mixed in the CsPbI3 perovskite precursor solution to stabilize the black phase of CsPbI3. In Chapter 6, a novel phenomenon, self-doping in MAPbI3 perovskite, was demonstrated and reported. MAPbI3 was found to be either n- or p-doped by changing the ratio of methylammonium halide (MAI) and lead iodine (PbI2) which are the two precursors for perovskite formationDoctor of Philosoph