For modern color-rendering applications, efficient blue, green, and red LEDs are required. While efficient green and red perovskite LEDs have been demonstrated, blue devices lag significantly behind due to the poor quality of chloride-based perovskites. Here, we show that doping manganese into blue perovskite nanocrystals increases their brightness and efficiency. By putting doped nanocrystals into LEDs, we see a 4-fold increase in efficiency, demonstrating that blue LEDs can be as efficient as their red and green cousins.

Utilizing solar energy to fix CO 2 with water into chemical fuels and oxygen, a mimic process of photosynthesis in nature, is becoming increasingly important but still challenged by low selectivity and activity, especially in CO 2 electrocatalytic reduction. Here, we report transition-metal atoms coordinated in a graphene shell as active centers for aqueous CO 2 reduction to CO with high faradic efficiencies over 90% under significant currents up to $60 mA/mg. We employed three-dimensional atom probe tomography to directly identify the single Ni atomic sites in graphene vacancies. Theoretical simulations suggest that compared with metallic Ni, the Ni atomic sites present different electronic structures that facilitate CO 2 -to-CO conversion and suppress the competing hydrogen evolution reaction dramatically. Coupled with Li + -tuned Co 3 O 4 oxygen evolution catalyst and powered by a triple-junction solar cell, our artificial photosynthesis system achieves a peak solar-to-CO efficiency of 12.7% by using earth-abundant transition-metal electrocatalysts in a pH-equal system.

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Recent advances in the development of perovskite solar cells based on CH 3 NH 3 PbI 3 have produced devices with power conversion efficiencies of >15%. While initial work in this area assumed that the perovskitebased cells required a mesoporous TiO 2 support, many recent reports have instead focused on the development of planar heterojunction structures. A better understanding of how both cell architecture and various design parameters (e.g., perovskite thickness and morphology) affect cell performance is needed. Here, we report the fabrication of perovskite solar cells based on a ZnO nanoparticle electron transport layer, CH 3 NH 3 PbI 3 light absorber, and poly(3-hexylthiophene) (P3HT) hole transport layer. We show that vapor-phase deposition of the PbI 2 precursor film produces devices with performances equivalent to those prepared using entirely solution-based techniques, but with very precise control over the thickness and morphology of the CH 3 NH 3 PbI 3 layer. Optimization of the layer thickness yielded devices with efficiencies of up to 11.3%. The results further demonstrate that a delicate balance between light absorption and carrier transport is required in these planar heterojunction devices, with the thickest perovskite films producing only very low power conversion efficiencies.

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