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

Formamidinium and guanidinium lead tri-iodide powders (FAPbI(3) and GUAPbI(3) respectively) were prepared by self-organization processes in solutions. The XRD analysis detected the formation, at room temperature, of a trigonal structure (alpha-FAPbI(3), space group P3m1), of a (non-perovskitic) hexagonal structure (delta-FAPbI(3), space group P63mc) for FAPbI(3), and the presence of orthorhombic (space group Pnma) and hexagonal structures for GUAPbI(3) respectively. The morphological investigation revealed the growth of aggregated (alpha-FAPbI(3) phase) and stripe-like crystallites (GUAPbI(3)) 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 alpha-FAPbI(3) and GUAPbI(3) 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 alpha-FAPbI(3)) and visible (Vis) ranges (for GUAPbI(3)). Films formation of GUAPbI(3) was demonstrated, and solar cells devices were fabricated with average power conversion of 0.3%. (C) 2015 Elsevier B.V. All rights reserved.