Investigation of formamidinium and guanidinium lead tri-iodide powders as precursors for solar cells

• The investigation of formamidinium and guanidinium lead iodide powders is reported.
• Photoluminescence properties of guanidinium containing system are demonstrated.
• Fabrication of devices starting from the dissolution of the prepared powders.

Formamidinium and guanidinium lead tri-iodide powders (FAPbI3 and GUAPbI3 respectively) were prepared by self-organization processes in solutions. The XRD analysis detected the formation, at room temperature, of a trigonal structure (α-FAPbI3, space group P3m1), of a (non-perovskitic) hexagonal structure (δ-FAPbI3, space group P63mc) for FAPbI3, and the presence of orthorhombic (space group Pnma) and hexagonal structures for GUAPbI3 respectively. The morphological investigation revealed the growth of aggregated (α-FAPbI3 phase) and stripe-like crystallites (GUAPbI3) respectively. The infrared spectra (IR) confirmed the strong influence of additional C–N bonds on vibrational properties of GUA-containing system. Optical absorption measurements indicated that α-FAPbI3 and GUAPbI3 systems reveal direct energy band gaps of 1.42 eV and 1.92 eV respectively at room temperature. Photoluminescence measurements revealed emissions in the infra-red (IR) (for α-FAPbI3) and visible (Vis) ranges (for GUAPbI3). Films formation of GUAPbI3 was demonstrated, and solar cells devices were fabricated with average power conversion of 0.3%.

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