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Perovskite processing for photovoltaics: a spectro-thermal evaluation

Author:
Williams, Alice E., Holliman, Peter J., Carnie, Matthew J., Davies, Matthew L., Worsley, David A., Watson, Trystan M.
Source:
Journal of materials chemistry A 2014 v.2 no.45 pp. 19338-19346
ISSN:
2050-7496
Subject:
Fourier transform infrared spectroscopy, annealing, desiccants, differential scanning calorimetry, hydrochloric acid, lead, manufacturing, phase transition, photovoltaic cells, silica gel, solar energy, solvents, stoichiometry, temperature, thermal degradation, thermogravimetry
Abstract:
Thermal analysis (TGA and DSC), coupled with evolved gas FTIR spectroscopy, has been used to study the changes occurring during, and differences between materials after, the annealing step of mixed-halide methylammonium lead halide perovskites. This is important because, to date, the material is the most efficient light harvester in highly efficient, 3ʳᵈ generation perovskite photovoltaic devices, and processing plays a significant role in device performance. TGA-FTIR data show only solvent evolution during the annealing step, whilst post-annealing analysis shows that the resulting material still contains a significant amount of residual solvent; however, efficient DMF removal was possible using a silica gel desiccant for a period of 3 days. The data also show that methylammonium halide decomposition does not occur until temperatures well above those used for perovskite processing, suggesting that this is not a significant issue for device manufacture. The absence of a well-defined, reversible tetragonal – cubic phase change around 55 °C in the DSC data of the annealed material, and the presence of HCl in evolved gas analysed following thermal decomposition, demonstrates that CH₃NH₃I₃₋ₓClₓ does retain some Cl after annealing and does not simply form stoichiometric CH₃NH₃PbI₃ as has been suggested by some workers.
Agid:
6708684