  Solar cells are semiconductor devices that generate electricity through
charge generation upon illumination. For optimal device efficiency, the
photo-generated carriers must reach the electrical contact layers before they
recombine. A deep understanding of the recombination process and transport
behavior is essential to design better devices. Halide perovskite solar cells
are commonly made of a polycrystalline absorber layer, but there is no
consensus on the nature and role of grain boundaries. This review paper
concerns theoretical approaches for the investigation of extended defects. We
introduce recent computational studies on grain boundaries, and their influence
on point defect distributions, in halide perovskite solar cells. We conclude
the paper with discussion of future research directions.
