  With rapidly growing photoconversion efficiencies, hybrid perovskite solar
cells have emerged as promising contenders for next generation, low-cost
photovoltaic technologies. Yet, the presence of nanoscale defect clusters, that
form during the fabrication process, remains critical to overall device
operation, including efficiency and long-term stability. To successfully deploy
hybrid perovskites, we must understand the nature of the different types of
defects, assess their potentially varied roles in device performance, and
understand how they respond to passivation strategies. Here, by correlating
photoemission and synchrotron-based scanning probe X-ray microscopies, we
unveil three different types of defect clusters in state-of-the-art triple
cation mixed halide perovskite thin films. Incorporating ultrafast
time-resolution into our photoemission measurements, we show that defect
clusters originating at grain boundaries are the most detrimental for
photocarrier trapping, while lead iodide defect clusters are relatively benign.
Hexagonal polytype defect clusters are only mildly detrimental individually,
but can have a significant impact overall if abundant in occurrence. We also
show that passivating defects with oxygen in the presence of light, a
previously used approach to improve efficiency, has a varied impact on the
different types of defects. Even with just mild oxygen treatment, the grain
boundary defects are completely healed, while the lead iodide defects begin to
show signs of chemical alteration. Our findings highlight the need for
multi-pronged strategies tailored to selectively address the detrimental impact
of the different defect types in hybrid perovskite solar cells.
