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The optoelectronic properties of organic lead halideperovskites（OLHPs） strongly depend on their underlying crystal symmetry and dynamics.Here, we exploit temperature-dependent synchrotron powder X-ray diffractionand temperature-dependent photoluminescence to investigate how thesubtle structural changes happening in the pure and mixed A-site cationMA1–xFAxPbBr3 （x = 0, 0.5, and 1） systems influencestheir optoelectronic properties. Diffraction investigations reveala cubic structure at high temperatures and tetragonal and orthorhombicstructures with octahedral distortion at low temperatures. Steadystate photoluminescence and time correlated single photon countingstudy reveals that the dual emission behavior of these OLHPs is dueto the direct-indirect band formation. In the orthorhombic phase ofMAPbBr3, the indirect band is dominated by self-trappedexciton （STE） emission due to the higher-order lattice distortionsof PbBr6 octahedra. Our findings provide a comprehensiveexplanation of the dual emission behavior of OLHPs while also providinga rationale for previous experimental observations.
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