This article investigates the role of excitons versus free charges in organo-lead tri-halide perovskites, which are promising materials for solar cells. The study uses optical spectroscopy to estimate the exciton binding energy in mixed-halide perovskite crystals, finding it to be in the range of 50 meV. This value is consistent with almost complete ionization of excitons under photovoltaic cell operating conditions. However, at higher photoexcitation densities, excitonic species become dominant, suggesting potential applications in various optoelectronic devices. Perovskite solar cells, first introduced in a dye-sensitized configuration, have shown significant progress, with power-conversion efficiencies exceeding 15%. The fundamental question in these cells is whether bound excitons or free charges are primarily responsible for photovoltaic mechanisms. To address this, the study determines the exciton binding energy in the room temperature crystal phase of the perovskite absorber and the branching ratio between free carriers and excitons under operating conditions. The researchers analyzed the temperature dependence of optical absorption in CH3NH3PbI3 and its mixed-halide analogue, CH3NH3PbI3−xClx. They observed a sharp excitonic transition at lower temperatures, attributed to a phase transition from tetragonal to orthorhombic structure. The exciton binding energy was estimated to be 55 ± 20 meV using the temperature-dependent absorption line width. This value indicates that free charges are predominantly generated and responsible for PV operation, similar to conventional inorganic semiconductors. The study also models the fraction of free charges versus excitons under thermodynamic equilibrium, showing that at room temperature, free charges dominate for realistic photoexcitation densities. The results suggest that the role of the heterojunction in perovskite solar cells is to enable selective charge collection, not to facilitate exciton ionization. The findings highlight the potential of perovskites for optoelectronic applications due to their ability to generate free charges efficiently.This article investigates the role of excitons versus free charges in organo-lead tri-halide perovskites, which are promising materials for solar cells. The study uses optical spectroscopy to estimate the exciton binding energy in mixed-halide perovskite crystals, finding it to be in the range of 50 meV. This value is consistent with almost complete ionization of excitons under photovoltaic cell operating conditions. However, at higher photoexcitation densities, excitonic species become dominant, suggesting potential applications in various optoelectronic devices. Perovskite solar cells, first introduced in a dye-sensitized configuration, have shown significant progress, with power-conversion efficiencies exceeding 15%. The fundamental question in these cells is whether bound excitons or free charges are primarily responsible for photovoltaic mechanisms. To address this, the study determines the exciton binding energy in the room temperature crystal phase of the perovskite absorber and the branching ratio between free carriers and excitons under operating conditions. The researchers analyzed the temperature dependence of optical absorption in CH3NH3PbI3 and its mixed-halide analogue, CH3NH3PbI3−xClx. They observed a sharp excitonic transition at lower temperatures, attributed to a phase transition from tetragonal to orthorhombic structure. The exciton binding energy was estimated to be 55 ± 20 meV using the temperature-dependent absorption line width. This value indicates that free charges are predominantly generated and responsible for PV operation, similar to conventional inorganic semiconductors. The study also models the fraction of free charges versus excitons under thermodynamic equilibrium, showing that at room temperature, free charges dominate for realistic photoexcitation densities. The results suggest that the role of the heterojunction in perovskite solar cells is to enable selective charge collection, not to facilitate exciton ionization. The findings highlight the potential of perovskites for optoelectronic applications due to their ability to generate free charges efficiently.