Researchers have overcome the extreme challenge of directly observing the dynamics of how light excites electrons and generates electricity in solar cell and photovoltaic technologies. The formation and dissociation of bound electron and hole pairs, known as excitons, were studied using a combination of broadband terahertz pulses (a trillion cycles per second) and selective laser pumping to reveal the light-induced excitation dynamics and charge transport mechanism within perovskites. Perovskites are a class of materials that show promise as industrial solar energy materials. Ultrafast spectroscopy provides an unambiguous approach to characterize genuine excitons and carriers and transition pathways. A particularly unique finding is that out-of-equilibrium excited quantum states are specifically revealed that dynamically evolve with a complex co-existence of excitons, unbound charge carriers, and phonons, e.g., even at what are considered long times after photoexcitation, 10’s of picoseconds (a trillionth of a second). This ultrafast characterization method is extremely relevant for understanding and potentially engineering high-speed electronic and optoelectronic devices. In the long run, the effects of internal excitonic quantum transitions and fundamental coherence provide a transformative opportunity to revolutionize field photovoltaic, quantum and optoelectronic technologies.
Ultrafast Terahertz Shapshots of Excitonic Rydberg States and Electronic Coherence in an Organometal Halide Perovskite