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M. Ibrahim Dar1 Michael Grätzel1

 

1, Ecole Polytechnique Federale de Lausanne, Lausanne, , Switzerland

The confluence of band gap modulation with the wide absorption range and spontaneous dissociation of excitons of hybrid organic-inorganic metal halide perovskites has led to the rapid evolution of efficient perovskite solar cells. The low temperature (<100 K) time-integrated photoluminescence of the methylammonium based perovskites CH3NH3PbI3 and CH3NH3PbBr3 revealed two well defined emission peaks, whereas formamidinium based perovskite, CH(NH2)2PbBr3 showed a single emission peak throughout the entire temperature range. Furthermore, the photoluminescence (PL) of perovskites irrespective of their composition, exhibited a continuous blueshift by raising the temperature from 15 K to 300 K. Density functional theory and classical molecular dynamics simulations allowed us to assign the additional PL peak observed in methylamonium based perovskites at low temperature to the presence of molecularly disordered orthorhombic phase, and also rationalizes that the unconventional blue shift of the PL peaks with the temperature is due to the thermal expansion of the lattice. In my presentation, I will discuss the temperature-dependence of band gap and decay dynamics of photoluminescence in various perovskites using time-integrated and time-resolved photoluminescence spectroscopy.

References:

Dar, M. I. et al. submitted.
Dar, M. I. et al. Sci. Adv. 2016, 2, e1601156.
Dar, M. I. et al. Adv. Funct. Mater. 2017, 27, 1701433.

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