Today, the economic and industrial growth in both developed and emerging countries is progressing at an unprecedented pace. Electricity generation causes a large fraction of greenhouse gases emission worldwide, so realistic alternatives to fossil fuels need to be sought by the scientific community. In this complex scenario, converting solar energy into electricity represents a much-needed solution to meet climate targets and move towards a low-carbon economy. Besides conventional single junction and multi-junction semiconductor photovoltaic devices, new solar cell technologies have evolved from the early 1990s1. However, research into hybrid organic-inorganic metal-halide perovskite solar cells (PSCs) has flourished only over recent years, attracting strong interest by the scientific community. Indeed, this emerging class of devices has become increasingly popular due to the opportunity of reaching a high power conversion efficiency, while being compatible with wet chemistry processing for large area devices. The excellent photovoltaic performance of halide perovskites goes along with a high photoluminescence yield that makes them suitable for a wide range of photonic devices and various optoelectronic applications, such as photodetectors, lasers and light emitting diodes. Moreover, wide band gap PSCs are serious candidate to be the top cell of tandem devices that uses the mature silicon technology as the bottom cell. The tremendous recent progress in PSCs originated from rapid advances in precursor formulation, fabrication methods and device architecture - however, most of the progress has been obtained through empirical device improvements, and several key questions still remain unanswered. Open issues include the optimal chemical composition of the perovskite films, ion migration, scalable fabrication routes, device architecture and stability in operation. PSCs were proven to degrade on a timescale varying from hours to weeks, depending on a number of potential degradation factors, both intrinsic (e.g. stoichiometry, interfaces) and extrinsic (e.g. light, humidity or temperature). The goal of PROPHET is to directly relate the photovoltaic behaviour of PSCs to their optical, electrical, chemical and morphological properties by investigating their photophysics on a range of different length and time scales. Specifically, the action aimed to determine the correlation between physical and chemical properties of hybrid perovskite thin films and their influence on the photovoltaic performance of full devices as well as understand through ex-situ and in-situ characterisation the main degradation processes affecting perovskite thin films and solar cells.
