Finding a more flexible mechanical sensor: Piezoelectric materials allow conversion between electricity and mechanical stresses. The most efficient piezoelectric materials are ceramics such as BaTiO ₃ or PbZrO ₃ , which are also extremely stiff. You et al. identified an organic perovskite structured piezoelectric material that is far more pliable yet has a piezoelectric response similar to that of traditional ceramics. This material may be a better option to use as a mechanical sensor for flexible devices, soft robotics, biomedical devices, and other micromechanical applications that benefit from a less stiff piezoelectric material. Science , this issue p. 306

Efficient all-perovskite tandem cells: Organic-inorganic perovskite films can boost the output of conventional silicon solar cells in tandem geometries by utilizing more of the light at the blue end of the solar spectrum. Tandem cells that use only perovskite films have been less successful because of the lack of a suitable material with a low bandgap that can replace silicon. Tong et al. report that a mixed tin-lead organic-inorganic material containing a small fraction of guanidinium thiocyanate has a low bandgap, long charge-carrier lifetime, and efficiencies around 25%. Science , this issue p. 475

A flexible strategy for piezoelectrics: Piezoelectric materials produce charge when they are deformed, making them ideal for various types of sensors. However, virtually all piezoelectric materials are ceramics, which are far from ideal for applications requiring flexible sensors. Liao et al. now describe a molecular material with piezoelectric properties comparable to the industry-standard ceramic lead zirconate titanate. The exceptional properties come from finding a molecular solid-solution series that allows for compositional optimization of the piezoelectric properties. Science , this issue p. 1206