Bulk and surface modifications for highly efficient and stable medium-bandgap hybrid perovskite solar cells

In today’s energy-transition scenario, the pursuit of efficient, cost-effective, and environmentally sustainable strategies to harvest renewable energy is accelerating. Solar cells are a promising solution for sustainable energy production, offering efficient photovoltaic energy conversion. Among these, perovskite solar cells have gathered significant attention due to their high efficiency and low-cost fabrication processes. However, the practical application and marketability of perovskite solar cells are limited by their scalability and long term stability. In their operation, interfaces between perovskite and adjacent charge transport layers are crucial components for improving both efficiency and stability of perovskite solar cells. Reactions between perovskite and transport layers significantly affect the device stability, while defects presented at the interfaces increase charge recombination possibilities which consequently deteriorates the final power conversion efficiency of the device. Interface passivation can be employed to modify these interfaces, promoting better charge collection efficiency and device stability. In this thesis, three interfaces of a medium-bandgap hybrid inverted perovskite solar cell are investigated. Different materials and deposition techniques are studied. Emphasis is brought on the analysis of the performance and of the thermal stability tested at 85°C under dark conditions in Nitrogen atmosphere. The devices are furthermore characterized using different spectroscopy techniques to gather further insight into the behaviour of the passivated devices. The results show enhanced performance for devices with a self-assembled monolayer used to passivate the hole transport layer, reaching efficiencies close to 21%, compared to untreated devices yielding 20%. The long-term thermal stability shows significant improvement by evaporating Caesium Iodide onto the perovskite, maintaining 64.6% of the initial performance after 1000 hours, while untreated devices retain only 19.5%. Attempts to treat the perovskite layer directly with self-assembled monolayers proved ineffective, resulting in performance deterioration.