In this paper the effects of post-deposition annealing followed by hydrogen ionimplantation on the properties of CuIn0.75Ga0.25Se2 thin films have been investigated. The samples were grown by flash evaporation onto glass substrates heated at temperature between room temperature and 200°C. Selected samples were subsequently processed under several sets of conditions, including vacuum, selenium, inert (argon) and forming gas (a 9:1 mixture of N2:H2) followed by hydrogen ion-implantation. A high resolution near-infrared photoacoustic spectrometer of the gas-microphone type was used for room temperature analysis of non-radiative defect levels in the as-grown, annealed and hydrogen implanted thin films. The absorption coefficient has been derived from the PA spectra to determine the gap energy and to establish the activation energies for several defect-related energy levels. The changes observed in the PA spectra following annealing and ionimplantation has been directly correlated with the compositional and structural properties of the samples.