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The family of organic-inorganic halide perovskite materials has generatedtremendous interest in the field of photovoltaics due to their high powerconversion efficiencies. There has been intensive development of cells based onthe archetypal methylammonium (MA)and recently introduced formamidinium (FA)materials, however, there is still considerable controversy over theirfundamental electronic properties. Two of the most important parameters are thebinding energy of the exciton (R$^{*}$) and its reduced effective mass $\mu$.Here we present extensive magneto optical studies of Cl assisted grownMAPbI$_{3}$ as well as MAPbBr$_{3}$ and the FA based materials FAPbI$_{3}$ andFAPbBr$_{3}$. We fit the excitonic states as a hydrogenic atom in magneticfield and the Landau levels for free carriers to give R$^{*}$ and $\mu$. Thevalues of the exciton binding energy are in the range 14 - 25 meV in the lowtemperature phase and fall considerably at higher temperatures for thetri-iodides, consistent with free carrier behaviour in all devices made fromthese materials. Both R$^{*}$ and $\mu$ increase approximately proportionallyto the band gap, and the mass values, 0.09-0.117 m$_{0}$, are consistent with asimple \textbf{k.p} perturbation approach to the band structure which can begeneralized to predict values for the effective mass and binding energy forother members of this perovskite family of materials.

Determination of the exciton binding energy and effective masses for the methylammonium and formamidinium lead tri-halide perovskite family