The development of organometal halide perovskite solar cells has grown rapidly and the highest efficiency of the devices has recently surpassed 22%. Because these solar cells contain toxic lead, a sustainable strategy is required to prevent environmental pollution and avoid healthy hazard caused by possible lead outflow. Here, in situ recycling PbI 2 from thermal decomposition CH 3 NH 3 PbI 3 perovskite films for efficient perovskite solar cells was developed. The thermal behavior of CH 3 NH 3 PbI 3 perovskite and its individual components were examined by thermogravimetric analysis. By optimizing the process of thermal decomposition CH 3 NH 3 PbI 3 film, the complete conversion from CH 3 NH 3 PbI 3 to pure PbI 2 layer with a mesoporous scaffold was achieved. The mesoporous structure readily promotes the conversion efficiency of perovskite and consequently results in high-performance device. A perovskite crystal growth mechanism on the mesoporous PbI 2 structure was proposed. These results suggest that in situ recycled PbI 2 scaffolds can be a new route in manipulating the morphology of the perovskite active layer, providing new possibilities for high performance. Meanwhile, the risk of lead outflow can be released, and the saving-energy fabrication of efficient solar cells can be realized.

A rapid annealing technique for fabricating perovskite materials via microwave radiation in air condition is presented. A planar-heterojunction perovskite device via microwave radiation within 6 min exhibits an efficiency of 10.29%, compared to 11.08% for a 90 minute heating-annealed device in inert atmosphere, which is higher than that (8.04%) of a heating-annealed device in air condition under high humidity (~60%). We believe that the microwave annealing technique provides a fast and less energy-intensive process for fabricating ideal perovskite active layers for high performance solar cells.

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We demonstrate the flexible and facile use of porous PbI2 layers to fabricate high quality perovskite films with a dense surface and without residual PbI2. PbI2 precursor solutions by adding polystyrene pore-forming agents are first spin-coated to fabricate the wet film. A porous PbI2 layer is formed by washing off polystyrene using organic solvents. The porous PbI2 layer not only serves as a channel for transporting the CH3NH3I solution but also offers extremely enlarged contact areas, facilitating interfacial reaction with CH3NH3I. Shiny smooth perovskite films with excellent electronic quality and solar cells with an efficiency up to 17% are obtained.

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