FAPbI3, FAPbBr3 and FAPbBr3-xIx perovskite thin films were 9 produced in a single step from a solution containing a mixture of FAI, PbI2, 10FABr, and PbBr2 (FA=Formamidinium). FAPbBr3-xIx perovskite thin films 11were deposited onto ITO-coated glass substrates by spin coating. X-ray 12 diffraction analyses confirmed that these thin film perovskites crystallize in the 13 cubic phase (Pm-3m) for all composition range 0 ≤ x ≤ 3. Mixed lead 14 perovskites showed a high absorbance in the UV-vis range. The optical 15 bandgap was estimated from spectral absorbance measurements. It was found 16 that the onset of the absorption edge for FAPbBr3-xIxthin films ranges between 17 1.47 and 2.20 eV for x=0 and x=3, respectively. Photoluminescence emission 18 energies for mixed halide perovskites were also dependent on their composition 19 and presented intermediate values from 810.4 nm for FAPbI 3 to 547.3 nm for 20 FAPbBr3. 21 22 B. Slimi et al. Monatsh Chem (2017) 148:835-844 DOI 10.1007/s00706-017-1958 Slimi et al. Monatsh Chem (2017) 148:835-844 DOI 10.1007/s00706-017-1958 3 Introduction 1 Organometal halide perovskites are currently one of the most actively 2 researched materials. They are typically composed of an organic group (A), 3 a metal ion (B), and one or two halides (X) forming the perovskite structure 4 ABX3. These hybrid perovskites have become one of the most attractive and 5 promising materials for photovoltaic over the last five years. In particular, 6 the methylammonium (MA) lead halide and formamidinium (FA) lead 7 halide perovskites, namely, CH3NH3PbX3 (or MAPbX3) and CH(NH2)2PbX3 8 (or FAPbX3) (X = Br, I, Cl) show remarkable properties for photovoltaic 9 applications [1-4] and light emitting diodes [5]. Solar power conversion 10 efficiencies of more than 20% have been reported [6], and tunable light 11 emitting diodes have been also reported [7]. Their low cost and ease of 12 production make them potential candidates for future technologies. Due to 13 their great absorption coefficient and high charge carrier mobility, these 14 groups of perovskites are well suited for converting solar energy [8, 9]. In 15 fact, halide perovskites drew an important impact in the field of thin film 16 photovoltaics in the last years, boosting up the energy conversion efficiency 17 from 3.8%,for the first perovskite-based solar cells in 2009 [1], up to more 18 than 20% [6,[10][11][12][13][14][15]. 19 Among these perovskites, MAPbI3is, by far, the most widely studied 20 perovskite for solar cell applications [13][14][15]. However, the FAPbI3 21 Slimi et al. Monatsh Chem (2017) 148:835-844 DOI 10.1007/s00706-017-1958 4 perovskite with broader light absorption has been attracting increasing 1 interest [6, 10,[16][17][18][19][20][21][22][23][24][25]. Like for MAPbI3, typical routes for depositing FAPbI3 2 perovskite thin films include one-step [6,18, 21] and sequential deposition 3 methods [6, 16,19] have been studied. More recently, many studies focusing 4 on material properties directly related to devic...
