Benjamin Foley1 Katelyn Dagnall1 Tianran Chen1 Yingzhong Ma2 Seung-Hun Lee1 Joshua Choi1

1, University of Virginia, Charlottesville, Virginia, United States
2, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

Metal halide perovskites (MHPs) are revolutionizing the solar cell research field - the record power conversion efficiency of MHPs based solar cells has reached 22%, which rivals that of silicon solar cells. This represents the highest efficiency among all solution processable materials and the fastest rate of efficiency improvement in the history of all photovoltaic materials. Based on this trend, MHPs have been called the “next big thing in photovoltaics” and worldwide research efforts have grown explosively.
Despite the impressive solar cell performance demonstrations, the microscopic mechanisms of the high performance are poorly understood, precluding more rational progress toward further increase in efficiency. In this talk, I will present our work that employed a combination of temperature dependent neutron scattering, X-ray diffraction and time resolved optical spectroscopy to study the role of organic cations in MHPs in determining the optoelectronic properties relevant for photovoltaic performance. Our findings show that the rotation of organic cations provides a major contribution to long charge carrier lifetime responsible for the high solar cell efficiency. Implications of our results in achieving improved performance with MHP solar cells will be discussed.