Optical characterisation of high-quality CuInSe2 thin films synthesised by two-stage selenisation process

Photoluminescence (PL) and optical absorption (OA) measurements in the temperature range from 4.2 to 300 K were carried out on CuInSe2 (CIS) thin films, synthesised on soda-lime glass substrates by a two-stage selenisation process. For near stoichiometric films, intense band-to-band recombination generated a room temperature PL peak at 1.028 eV with full width at half maximum (FWHM) of approximately 50 meV. At 78 K, the A and B free exciton peaks appeared, in both PL and OA spectra, merged into a band at approximately 1.044 eV. The 4.2 K-PL spectrum contains a number of features. The A and B excitonic peaks shift to 1.0409 eV (A) and 1.0444 eV (B) and are well resolved in both the PL and OA spectra, with their FWHM reduced to 2.5 meV. Their spectral positions and FWHM are approaching those in high quality CIS single crystals. The absorption coefficient *a is derived from the OA spectra. Defects responsible for the observed PL bands are discussed.