Photophysics and solar cell devices of two dimensional perovskites

Hybrid lead halide perovskites materials are advancing the frontiers of photovoltaics and light emission, producing unprecedented performances for solution process devices, such as 25% efficient solar cells and 20% efficient LEDs. However some materials limitations still await convincing resolution, namely stability against degradation caused by water, oxygen and light needs to be improved and the content of lead in the perovskite formulation should be avoided to prevent environmental contamination. In this thesis, 2D perovskites have been investigated as a more stable alternative to 3D counterparts, since the large hydrophobic organic cations embedded in the structure provide a barrier for oxygen and water. 2D lead perovskite have been widely studied and to grow oriented thin film is a hot spot for high efficiency solar cells. Here, we employed quasi-2D lead perovskite PEA2MA4Pb5I16 (n=5) as light absorber for solar cell devices. We applied a vacuum-assisted method for film growth and a different hole transport layer for solar cell device. We successfully improved the PCE to 14.14 % by these processing. Tin perovskite is a potential candidate for lead-free perovskite, with the device PCE approaching to 10%. Different from lead perovskite, light-generated charge carriers of tin perovskites are not investigated much. Here, we fabricated BA2SnI4 (n=1) and BA2MASn2I7 (n=2) thin films and studied the charge carrier behavior by ultrafast optical measurements.