Nature: potassium passivated halogenated perovskite to maximize and stabilize luminescence

Metal halide perovskite is a kind of ion semiconductor material with great potential After just a few years of development, it can be compared with commercial thin film photovoltaic materials in photoelectric conversion efficiency Perovskite is cheap and can be produced at low temperatures, making it a strong candidate for the next generation of solar cells and lighting materials Despite the huge potential of perovskite, there are still some limiting factors that hinder the improvement of its efficiency and stability The easier it is for electrons to move in solar cell materials, the more efficient it is for materials to convert light energy into electricity The tiny defects in perovskite crystal structure will "trip" the electron before its energy is utilized, which is called non radiation loss Although the band gap of perovskite can be adjusted continuously by modifying the chemical composition, the luminous efficiency of the most advanced perovskite solar cells is still far lower than 100% under the standard sunlight condition due to the limitation of non radiation loss Another problem is that in the mixed halogenated perovskite system designed for continuous band gap adjustability (band gap is about 1.7-1.9 V), the migration of ions induced by light makes the band gap unstable Recently, an international research team led by Sam stranks, a Cavendish Laboratory at Cambridge University, found that the addition of potassium iodide can break the limitation of the luminous efficiency of perovskite solar cells The team proved that by modifying the surface and grain boundary of perovskite with passivated potassium halide layer, the non radiation loss and photoinduced ion migration defects of perovskite can be improved, reaching 66% of the quantum yield of external photoluminescence and more than 95% of the internal yield The new perovskite can not only achieve high luminous efficiency, but also maintain a high mobility of 40 cm 2 v-1s-1 When it is connected with the electrode of solar cell device, the external luminous yield is still as high as 15%, indicating that the interface of calcium titanium ore layer is very clean Relevant papers were published on nature under the title of "maximizing and stabilizing luminescences from halide perovskites with potassium activation" (DOI: 10.1038 / nature25989) Figure 1 Enhancement of radiation efficiency and charge carrier mobility by passivation (source: nature) in this study, the researchers changed the chemical composition of perovskite by adding potassium iodide to the perovskite ink and then self assembling it into a thin layer This technology is compatible with the precise winding alignment process, which means that the technology is scalable and cheap Potassium iodide forms a modified layer on the top of perovskite, which can improve the defects in the crystal, so that the electron can move more freely, and can fix the ion movement to achieve a more stable band gap The researchers showed the calcium titanium layer with ideal performance, and superimposed it with silicon solar cells or other calcium titanium layers to form series solar cells By adding layers of calcium and titanium, solar cells can collect light energy from a wider spectrum The device composed of perovskite and potassium has good stability in the test The photoelectric conversion efficiency is 21.5%, which is similar to the best perovskite based solar cell, and not far from the actual limit (29%) of silicon-based solar cell The series cell consists of two layers of perovskite with ideal band gap The theoretical efficiency limit is 45% and the actual limit is 35% Both parameters are higher than the actual limit of silicon solar cell Figure 2 Enhanced solar cell power conversion efficiency (source: nature) correspondent: Dr Sam banks