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Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m−2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date.

Stacking solar cells with decreasing band gaps to form tandems presents the possibility of overcoming the single-junction Shockley-Queisser limit in photovoltaics. The rapid development of solution-processed perovskites has brought perovskite single-junction efficiencies >20%. However, this process has yet to enable monolithic integration with industry-relevant textured crystalline silicon solar cells. We report tandems that combine solution-processed micrometer-thick perovskite top cells with fully textured silicon heterojunction bottom cells. To overcome the charge-collection challenges in micrometer-thick perovskites, we enhanced threefold the depletion width at the bases of silicon pyramids. Moreover, by anchoring a self-limiting passivant (1-butanethiol) on the perovskite surfaces, we enhanced the diffusion length and further suppressed phase segregation. These combined enhancements enabled an independently certified power conversion efficiency of 25.7% for perovskite-silicon tandem solar cells. These devices exhibited negligible performance loss after a 400-hour thermal stability test at 85°C and also after 400 hours under maximum power point tracking at 40°C.

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Thermally-induced tensile strain that remains in perovskite films following annealing results in increased ion migration and is a known factor in the instability of these materials. Previously-reported strain regulation methods for perovskite solar cells (PSCs) have utilized substrates with high thermal expansion coefficients that limits the processing temperature of perovskites and compromises power conversion efficiency. Here we compensate residual tensile strain by introducing an external compressive strain from the hole-transport layer. By using a hole-transport layer with high thermal expansion coefficient, we compensate the tensile strain in PSCs by elevating the processing temperature of hole-transport layer. We find that compressive strain increases the activation energy for ion migration, improving the stability of perovskite films. We achieve an efficiency of 16.4% for compressively-strained PSCs; and these retain 96% of their initial efficiencies after heating at 85°C for 1000 hoursthe most stable wide-bandgap perovskites (above 1.75 eV) reported so far.