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Improved perovskite photovoltaic performance
A recent entry in the solar cell race is perovskite cells, named for the structure adopted by salt made from metal halides and organic cations that absorb the light and generate charges. The charges generated have to be transferred to a metal oxide (typically titanium oxide), and some of these charge carriers are lost in the transfer. Mei et al. made this process more efficient by growing a more crystalline perovskite with fewer defects inside porous versions of titanium and zirconium oxide. They added a second organic cation that stuck to the pore walls and directed the growth of the perovskite crystals. The improved solar cells operated for more than 1000 hours under full sunlight.
Science, this issue p. 295
We fabricated a perovskite solar cell that uses a double layer of mesoporous TiO2 and ZrO2 as a scaffold infiltrated with perovskite and does not require a hole-conducting layer. The perovskite was produced by drop-casting a solution of PbI2, methylammonium (MA) iodide, and 5-ammoniumvaleric acid (5-AVA) iodide through a porous carbon film. The 5-AVA templating created mixed-cation perovskite (5-AVA)x(MA)1-xPbI3 crystals with lower defect concentration and better pore filling as well as more complete contact with the TiO2 scaffold, resulting in a longer exciton lifetime and a higher quantum yield for photoinduced charge separation as compared to MAPbI3. The cell achieved a certified power conversion efficiency of 12.8% and was stable for >1000 hours in ambient air under full sunlight.