| Autor: |
Zhao D; Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.; Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, U.K., Flavell TA; Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.; Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, U.K., Aljuaid F; Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.; Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, U.K., Edmondson S; Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, U.K., Spencer BF; Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.; Henry Royce Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K., Walton AS; Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.; Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, U.K., Thomas AG; Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.; Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.; Henry Royce Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K., Flavell WR; Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.; Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, U.K. |
| Abstrakt: |
Since the emergence of organometal halide perovskite (OMP) solar cells, there has been growing interest in the benefits of incorporating polymer additives into the perovskite precursor, in terms of both photovoltaic device performance and perovskite stability. In addition, there is interest in the self-healing properties of polymer-incorporated OMPs, but the mechanisms behind these enhanced characteristics are still not fully understood. Here, we study the role of poly(2-hydroxyethyl methacrylate) (pHEMA) in improving the stability of methylammonium lead iodide (MAPI, CH 3 NH 3 PbI 3 ) and determine a mechanism for the self-healing of the perovskite-polymer composite following exposure to atmospheres of differing relative humidity, using photoelectron spectroscopy. Varying concentrations of pHEMA (0-10 wt %) are incorporated into a PbI 2 precursor solution during the conventional two-step fabrication method for producing MAPI. It is shown that the introduction of pHEMA results in high-quality MAPI films with increased grain size and reduced PbI 2 concentration compared with pure MAPI films. Devices based on pHEMA-MAPI composites exhibit an improved photoelectric conversion efficiency of 17.8%, compared with 16.5% for a pure MAPI device. pHEMA-incorporated devices are found to retain 95.4% of the best efficiency after ageing for 1500 h in 35% RH, compared with 68.5% achieved from the pure MAPI device. The thermal and moisture tolerance of the resulting films is investigated using X-ray diffraction, in situ X-ray photoelectron spectroscopy (XPS), and hard XPS (HAXPES). It is found that exposing the pHEMA films to cycles of 70 and 20% relative humidity leads to a reversible degradation, via a self-healing process. Angle-resolved HAXPES depth-profiling using a non-destructive Ga Kα source shows that pHEMA is predominantly present at the surface with an effective thickness of ca. 3 nm. It is shown using XPS that this effective thickness reduces with increasing temperature. It is found that N is trapped in this surface layer of pHEMA, suggesting that N-containing moieties, produced during reaction with water at high humidity, are trapped in the pHEMA film and can be reincorporated into the perovskite when the humidity is reduced. XPS results also show that the inclusion of pHEMA enhances the thermal stability of MAPI under both UHV and 9 mbar water vapor pressure. |
