Anisotropic excitonic absorption in SbI3 films: Theory and experiment

•Optical properties of monoclinic SbI3 are investigated using DFT calculations and experiment.•The calculated absorption spectra of six (hkl) planes show highly anisotropic nature.•2.66 eV or 2.7 eV are possible indirect band gaps from band structure compared to measured 2.8 eV.•One exciton appears at 3.56 eV for (hkl) oriented film and two excitons at 2.95 eV and 3.30 eV for (130)•The experimental and theoretical optical properties match reasonably well.