The research and development of Lead Halide perovskite solar cells is one of the most rapidly growing research areas. Since the discovery of these organic-inorganic metal halide perovskite solar cells in 2009, the devices have shown great promise, with efficiency up to over 20%. This efficiency is a factor 4 greater than organic semiconductor solar cells and the materials are cheaper compared to the traditional inorganic semiconductors such as silicon. Due to the rapid development of devices with the aim to get them to market, less work has been done on understanding the fundamental science, such that there are issues with the lifetime, the reliability and reproducibility of the materials and devices. This proposal looks to investigate these materials using the avoided level crossing technique, to provide further information on the underlying mechanisms, hence help bring them to market.