Large‐area flexible, transparent, and highly luminescent films containing lanthanide (III) complex‐doped ionic liquids for efficiency enhancement of silicon‐based heterojunction solar cell

ABSTRACT Ionic liquid (IL)‐based lanthanide luminescent materials with luminescent downshifting properties are beneficial for enhancing the photovoltaic energy conversion efficiency ( η pv ) of silicon‐based solar cells. Herein, novel lanthanide (III) complex‐doped ILs have been successfully prepared by simply dissolving the complex Ln(pybox) 3 (Ln = Eu or Tb, pybox = 2,6‐bis[(4 R )‐4‐phenyl‐2‐oxazolinyl]pyridine) into a bidentate organophosphine functionalized IL (1,3‐bis‐[3‐(diphenylphosphinyl)propyl]imidazolebis (trifluoromethylsulfonyl)imide), showing improved luminescence efficiency attributed to the coordination of ILs with Ln 3+ ions and thus occurrence of the energy transfer from ILs to Ln 3+ ions and very high absolute quantum efficiency (up to 97.22%). Large area (17 × 17 cm 2 ) flexible, transparent, and luminescent poly(methyl methacrylate) thin films were prepared through a simple drop‐casting method and were applied as luminescent downshifting coatings to the silicon‐based heterojunction solar cells (active area: 235 cm 2 ). In the best case using the Tb 3+ ‐containing film, the η pv of the solar cell increases from 16.676 to 16.774%.