Physical and Analytical Chemistry Seminar
Lecturer: Dr. Omer Yaffe
Location: Faculty Seminar Room
Power conversion efficiency of solar cells based on hybrid (organic-inorganic) lead-halide perovskites has been rapidly increasing and is now over 20%. In an attempt to explain these remarkable results, theoretical studies have suggested that dynamic disorder, imposed by the rotation of anisotropic organic molecules in the inorganic octahedral network, plays a key role in determining its electronic properties and high photovoltaic activity.
I will present an experimental study that is aimed to understand the nature of dynamic disorder and its implications on carrier transport, carrier recombination and photovoltaic efficiency of these fascinating materials.
Using low-frequency Raman scattering as a probe, I will compare the structural dynamic properties of CH3NH3PbBr3, a hybrid lead-halide perovskite and CsPbBr3, an all-inorganic perovskite crystal. Both are of the general ABX3 perovskite chemical composition, have a similar band gap and similar structural phase sequence with temperature. The main finding is that the dynamic structural disorder is native to the ABX3 framework, including both the tilting motion of lead-halide octahedra and the off-center displacement of A cations. Hence, the lead halide perovskite crystals are dynamically disordered irrespective of rotation of the anisotropic organic molecule.
This study provides important design rules for new, more stable and efficient materials for photovoltaic applications.