1 research outputs found
Transient Photovoltage in Perovskite Solar Cells: Interaction of Trap-Mediated Recombination and Migration of Multiple Ionic Species
It
is highly probable that perovskite solar cells (PSCs) are mixed
electronic-ionic conductors, with ion migration being the driving
force for PSC hysteresis. However, there is much that is not understood
about the interaction of ion migration with other processes in the
cell. The key question is: what factors of a PSC are influenced when
ions are free to move? In this contribution, we employ a numerical
drift-diffusion model of PSCs to show that the migration of both anions
and cations in interaction with trap-mediated recombination in the
bulk and/or at the surfaces of the perovskite absorber can manifest
both current–voltage hysteresis and unusual nonmonotonic PSC
photovoltage transients. We identify that a key mechanism of this
interaction is the influence of the net ionic charge throughout the
perovskite bulkî—¸which varies as the ions approach new steady-state
conditionsî—¸on the distribution of electrons and holes and subsequently
the spatial distribution of trap-mediated recombination modeled after
Shockley Read Hall (SRH) statistics. Relative to intrinsic recombination
mechanisms, SRH recombination can be highly sensitive to local asymmetries
of the electron–hole population. We show that this sensitivity
is key to replicating nonmonotonic transients with multiple time constants,
the forms of which may have suggested multiple processes. This work
therefore supports the conceptualization of the hysteretic behavior
of PSCs as dominated by the interplay between ion migration and trap-mediated
recombination throughout the perovskite absorber