There is an enormous variety of exotic properties in the methylammounium triiodideplumbate perovskite and related photovoltaic perovskites. A range of important questions are being discussed in meetings and papers. If there is consensus about one point among the main theorists of the field, it is that it is extremely unlikely that excitons persist for any significant time, due to dielectric screening. This view has been clearly expressed in the following papers
Frost, J. M.; Butler, K. T.; Brivio, F.; Hendon, C. H.; van Schilfgaarde, M.; Walsh, A. “Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells”. Nano Letters 2014, 14, 2584-2590. (They state: It is clear that excitons will not play a significant role in the photovoltaic device physics.)
Menendez-Proupin, E.; Palacios, P.; Wahnon, P.; Conesa, J. C. “Self-consistent relativistic band structure of the CH3NH3PbI3 perovskite”. Physical Review B 2014, 90, 045207.
Analysis of Multivalley and Multibandgap Absorption and Enhancement of Free Carriers Related to Exciton Screening in Hybrid Perovskites, Jacky Even, Laurent Pedesseau, and Claudine Katan, 2014, 118 (22), pp 11566–11572 (” Our analysis suggests exciton screening by collective orientational motion of the organic cations at room temperature, leading to almost free carriers.”)
For experimental results see