Suppression of deep level defects in CIGS solar cells using proton implantations

The suppression effect on deep level defects and the defect generation in Cu(InGa)Se₂ solar cells by a proton implantation have been investigated using deep level transient spectroscopy (DLTS) and optical DLTS measurements. CIGS films with the thickness of ~3μm were grown on a soda-lime glass as substrate by co-sputtering method and implanted by proton with 2× 10¹⁶ cm^-3 dose and in 50 keV energy, and post-annealed under various conditions. To study the proton effect on deep level defects in CIGS films, DLTS and ODLTS were carried out and 5 hole traps and 3 electron traps were found. The calculated trap energies and densities for observed traps were summarized. After proton implantation and post annealing at 200°C for 5 min in N₂ ambient, the deep defects which is known to attribute to loss of the CIGS solar cell efficiency were remarkably reduced in intensity. Therefore, we report that electrical deep level defects in CIGS films can be passivated by proton implantation and post annealing and that a deep level defect with the activation energy of E_v+0.28 eV generates newly.