Small grains as recombination hot spots in perovskite solar cells

Despite a decade of research, much remains unknown about the role that grain boundaries play in determining the photovoltaic performance of perovskite solar cells. In this talk, I will describe how by combining experimental studies with theoretical device simulations, we find that the recombination at grain boundaries is diffusion limited and depends on the grain area with small grains acting as recombination hot spots. We show that the distribution of grain sizes not only influences the overall performance of perovskite solar cells, but also leads to significant current exchange between small and large grains at open-circuit conditions.