Effect of temperature on structural phase transition and photoluminescence in organic-inorganic hybrid CH₃NH₃PbI_3-xCl_x perovskite

Organic-inorganic hybrid (CH3NH3PbI3-xClx) perovskite is a useful light accumulating material. Its characteristic features are found to be very sensitive to synthesis and environmental conditions. We studied its structural phase transformation, inter band transitions, and photoluminescence as a function of temperature, which are key parameters governing its light absorbing characteristics. We found that photoluminescence peaks exhibit several finer features, which are identified, deconvoluted, and discussed in detail. Our analyses revealed the presence of multiple phases, defects (mainly Cl), excitonic binding energies, and radiative recombination of trap states in the perovskite. Based on the results, a schematic energy band diagram has been proposed, and it is concluded that the trap states will become less active at elevated temperatures. Moreover, increased post annealing temperature will decrease the recombination at interfaces due to improved crystallinity and large grain sizes. Control over the surface and interface trapping by using the appropriate working and annealing temperature for the device may be key to increasing the efficiency of perovskite based solar cells.