Defect Passivation and Phase Stabilization of Metal Halide Perovskites toward Efficient Optoelectronic Devices

Promovendus/a: Handong Jin

Promotor(en): Prof. dr. Johan Hofkens, Mevrouw Elke Debroye

Solar energy as clean and renewable resource has been a hot topic due to the environmental deterioration and lack of oil. So far, many semiconductor materials have been investigated for their efficiency as solar cells. It is still of great interest and practical importance to develop low-cost, effective photoactive materials for photovoltaic applications. Over the past few years, there is a growing interest in lead halide perovskites as promising materials for photovoltaic applications due to their appropriate bandgap, strong light absorption, defect tolerance, and long carrier diffusion lengths. However, the power conversion efficiencies and long-term stability are still two major hurdles preventing the long-term commercial profit of perovskite solar cells. The main causes are inevitable harmful lattice defects during crystal growth and easy phase transition under external stimuli. Firstly, to overcome these harmful defects, defect passivation is usually performed in lead halide perovskite materials for obtaining a higher performance. Chloride ions have been seen as prominent candidates, for passivating intrinsic and extrinsic surface defects. However, conclusive experimental evidence on chloride-induced trap passivation has not been provided yet. Moreover, the chloride post-treatment targeting surface passivation usually results in decreasing photovoltaic efficiencies. This dissertation provides detailed studies on passivating intrinsic and extrinsic defects, by exploring the morphology, structure, and optical properties upon chloride incorporation and post-treatment of methylammonium lead iodide perovskite nanoparticles (MAPbI3). Secondly, phase stability is the main issue on the optoelectronic application of full inorganic cesium lead iodide (CsPbI3) perovskite. In this project, a novel strain method is developed in to obtain a stable photoactive black phase of CsPbI3.