  Next-generation low-cost semiconductors such as halide perovskites exhibit
optoelectronic properties dominated by nanoscale variations in their structure,
composition and photophysics. While microscopy provides a proxy for ultimate
device function, past works have focused on neat thin-films on insulating
substrates, missing crucial information about charge extraction losses and
recombination losses introduced by transport layers. Here we use a multimodal
operando microscopy toolkit to measure nanoscale current-voltage curves,
recombination losses and chemical composition in an array of state-of-the-art
perovskite solar cells before and after extended operational stress. We apply
this toolkit to the same scan areas before and after extended operation to
reveal that devices with the highest performance have the lowest initial
performance spatial heterogeneity - a crucial link that is missed in
conventional microscopy. We find that subtle compositional engineering of the
perovskite has surprising effects on local disorder and resilience to
operational stress. Minimising variations in local efficiency, rather than
compositional disorder, is predictive of improved performance and stability.
Modulating the interfaces with different contact layers or passivation
treatments can increase initial performance but can also lead to dramatic
nanoscale, interface-dominated degradation even in the presence of local
performance homogeneity, inducing spatially varying transport, recombination,
and electrical losses. These operando measurements of full devices act as
screenable diagnostic tools, uniquely unveiling the microscopic mechanistic
origins of device performance losses and degradation in an array of halide
perovskite devices and treatments. This information in turn reveals guidelines
for future improvements to both performance and stability.
