A three-dimensional quantum dot network stabilizes perovskite solids via hydrostatic strain

Compressive strain engineering improves perovskite stability. Twodimensional compressive strain along the in -plane direction can be applied to perovskites through the substrate; however, this in -plane strain results in an offsetting tensile strain perpendicular to the substrate, linked to the positive Poisson ratio of perovskites. Substrateinduced strain engineering has not yet resulted in state-of-the-art operational stability. Here, we seek instead to implement hydrostatic strain in perovskites by embedding lattice -mismatched perovskite quantum dots (QDs) into a perovskite matrix. QD-in-matrix perovskites show a homogeneously strained lattice as evidenced by grazing -incidence X-ray diffraction. We fabricate mixed -halide wide -band -gap (E-g; 1.77 eV) QD-in-matrix perovskite solar cells that maintain >90% of their initial power conversion efficiency (PCE) after 200 h of one -sun operation at the maximum power point (MPP), a significant improvement relative to matrix -only devices, which lose 10% (relative) of their initial PCE after 5 h of MPP tracking.