Despite rapid progress in the efficiency of organohalide perovskite based solar cells, physical mechanisms underlying their efficient charge separation and slow charge recombination still elude us. In this work, we provide first direct evidence of spontaneous charge separation via first-principles simulations.
The excitons are predicted to self-organize into stripes of photo-excited electrons and holes, spatially separated as effective channels for charge transport. The rotation of organic cations deforms the inorganic framework, and as the deformation reaches a critical value, a direct band gap transforms to an indirect one, and the photo-excited electrons rotate in alignment with the deformation-induced electric fields. The interplay between dynamic disorder, ionic bonding, and polarization is responsible for the formation of the charge stripes and the indirect band gap, both of which could lead to efficient charge separation and reduced charge recombination in the organohalide perovskites.
(Image, Left) CSUN PREM students participated the REU program at Princeton in the summer 2016. These students were housed on the Princeton campus and benefitted both from formal REU program events and from interaction with a larger group of REU students. The CSUN students were supervised by Princeton faculty members and their graduate students to carry out various research projects in Materials Science and Engineering.