Probing Exciton States in Hybrid Perovskite Semiconductors

Hybrid Organic-Inorganic Perovskites are a new generation of photovoltaic semiconductors that do not use scarce metals. Study of the viability of these materials involves detailed understanding of the various states an electron may go through in the material. Exciton states are bound excited electronic states just below the conduction band where the electron is essentially orbiting the “hole,” or positive charge, left behind by the promotion of an electron to the conduction band. These exciton states guard the transition between free and lattice electron, but their dynamics and timescales are not yet well understood. Proper characterization of the electron lifetime in the material involves understanding the timescales, and vibrational dynamics of these loosely bound states. We report an optically pumped, time resolved terahertz spectrum of MAPbBr3, a well-studied hybrid perovskite. Transitions between exciton states are resonant in the far-IR, or terahertz region of the electromagnetic spectrum, an area that has been difficult to study until relatively recent advances in generation and detection of this light. Obtaining details of the internal exciton dynamics between hydrogen-atom like states of electron-hole pairs provides an important piece of information for the directed evolution of this promising family of materials.