Characterization of mixed-ion perovskite solar cells prepared under different conditions.

In a time of global warming and increasing demand of energy, solar power is evidently an alternate source to the fossil fuels and nuclear resources. These two are declining in terms of quantity and popularity. Silicon solar cells have been developed for many years improving their efficiency and production. These progresses have reached their limits and new photovoltaic devices are emerging into this field. In the last few years many studies have been achieved on Perovskite materials showing high yield improvements and an ease of fabrication. However their stability in outdoor conditions remains an issue and a path of enhancement. Perovskite was mentioned by Miyasaka and his co-workers for solar cells in 2009. The perovskite solar cells consist of a succession of various active layers, the perovskite as the core absorber is connected to charge transporting materials leading to a Power Conversion Efficiency (PCE) above 22% and a higher stability. Here the material introduced is a mixed cation organo-lead halides perovskite connected to an electron transporting material (ETM) as well as a hole transporting material (HTM) layers. The ETM is made of different layers of titanium oxide while the HTM is mostly composed by spiroOMeTAD. Numerous samples were prepared with the same perovskite composition ((FAPbI3)0.85/ (MAPbBr3)0.15) by one step spin-coating. First many configurations of synthesis were tried with the aim of appreciating their influence on the perovskite thickness and purity. These properties being directly connected to the absorption of the compound, UV-Vis spectra were recorded. X-ray diffraction analysis were also performed to check the crystallinity of the perovskite and the present phases. Several samples were fully synthesized into solar cells with the deposition of gold counterelectrodes. Photovoltaic parameters and efficiencies were then measured thanks to a potentiostat and a light imitating sun. A SEM imagery was used to observe the different layers, their thickness and morphology. In order to have a global view of the charges carriers lifetime and to calculate the series resistance of the samples the Electrochemical Impedance Spectroscopy was performed. Emission decays measured by Time-Correlated Single-Photon Counting after the excitation with pico-second laser were used to get the information on the charge carriers decay to understand the recombination processes.