Fig. 2: UV-vis absorption spectra of thin films having Y6 and ITIC dispersed in PVK.

UV-vis absorption spectra of solid-state thin films having different loading ratios (1–100 wt%) of a Y6 and b ITIC in a PVK matrix. c Spectral shift (eV) and d spectral broadening (eV) for different concentrations of Y6 (red symbols with dashed line) and ITIC (black symbols with dashed line) relative to those in solution. The spectral shift is defined as the energy difference of the maximum absorption intensity between thin films and solution. The spectral broadening is calculated by finding the difference in spectral full-width half maximum (FWHM) between thin films and solution.