FA<sub>0.88</sub> Cs<sub>0.12</sub> PbI<sub>3-</sub><sub>x</sub> (PF<sub>6</sub> )<sub>x</sub> Interlayer Formed by Ion Exchange Reaction between Perovskite and Hole Transporting Layer for Improving Photovoltaic Performance and Stability.
basic_science · Level V
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- Record sourced from PubMed, PMID 30141262.
- Also identified by DOI 10.1002/adma.201801948.
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Abstract
Interface engineering to form an interlayer via ion exchange reaction is reported. A FA<sub>0.88</sub> Cs<sub>0.12</sub> PbI<sub>3</sub> formamidinium (FA) perovskite layer is first prepared, then FAPF<sub>6</sub> solution with different concentrations is spin-coated on top of the perovskite film, which leads to a partial substitution of iodide by PF<sub>6</sub><sup>-</sup> ion. The second phase with nominal composition of FA<sub>0.88</sub> Cs<sub>0.12</sub> PbI<sub>3-</sub><sub>x</sub> (PF<sub>6</sub> )<sub>x</sub> is grown at the grain boundary, which has island morphology and its size depends on the FAPF<sub>6</sub> solution concentration. The lattice is expanded and bandgap is reduced due to inclusion of larger PF<sub>6</sub><sup>-</sup> ions. The power conversion efficiency (PCE) is significantly enhanced from 17.8% to 19.3% as a consequence of improved fill factor and open-circuit voltage (V<sub>oc</sub> ). In addition, current-voltage hysteresis is reduced. Post-treatment with FAPF<sub>6</sub> reduces defect density and enhances carrier lifetime, which is responsible for the improved photovoltaic performance and reduced hysteresis. The unencapsulated device with post-treated perovskite film demonstrates better stability than the pristine perovskite, where the initial PCE retains over 80% after 528 h exposure under relative humidity of around 50-70% in the dark and 92% after 360 h under one sun illumination.