Nature Materials 16, 522–525 (2017); published online 7 November 2016; retracted after print 20 December 2017.

The authors of the study are retracting this Letter due to concerns about the reproducibility of the photovoltaic architecture performance presented, and with the interpretation of the data included in the manuscript and Supplementary Information. This Letter presented solar cells based on two perovskite layers separated by a monolayer of hexagonal boron nitride, deposited on graphene aerogel. The large variability of the current–voltage and spectral response of nominally identical devices and the rapid time evolution of key photovoltaic parameters undermine the authors' confidence in the conclusions that can be drawn at this stage regarding the performance of these architectures, and they therefore wish to retract the Letter. All the authors agree with the retraction.