Characterization and performance of Cu( In, Ga)Se-2 thin films incorporating low-temperature pre-annealing process

This paper focuses on the characterization and performance evaluation of the Cu(In, Ga)Se-2 (CIGS) thin films fabricated using the low-temperature pre-annealing process, followed by the plasma-enhanced Se vapor selenization coupled with etching (PESVSE) and thermal-assisted Se vapor selenization (TASVS). The XPS data reveals that the increase of pre-annealing temperature can facilitate the diffusion of Ga towards the surface of CIGS thin film by stabilizing more Ga distribution on the surface of the annealed precursor. The PESVSE process can effectively increase Ga content on the film surface with the help of low-temperature pre-annealing process. Results also indicate that the PESVSE combined with a low-temperature pre-annealing process can significantly weaken and even eliminate the adverse phase separation to yield a single-phase CIGS thin film with a moderate Ga content. The PESVSE process helps to improve and even achieve a homogeneous depth distribution of Ga in the whole CIGS thin film in comparison with the TASVS process. The PESVSE process achieves a higher open circuit voltage and also higher conversion efficiency of CIGS solar cell treated by the low-temperature pre-annealing process. The feasibility of using this low-temperature pre-annealing method to make high-quality CIGS thin films for photovoltaic applications has been successfully validated in this work. (C) 2017 Elsevier B.V. All rights reserved.