Coupled effect of pre-alloying treatment and plasma-assisted Se vapor selenization process in Cu(In, Ga)Se2 thin film

In this work, we investigate the compositional, structural, morphological properties of CIGS film obtained from a plasma-assisted Se vapor selenization process (PASVS) coupled with a pre-alloying treatment. For comparison, a thermal-assisted Se vapor selenization process (TASVS) is also tested. A higher annealing temperature is more able to enhance the element interdiffusion of precursor film, which helps reduce the indium loss and also improve the crystallinity of CIGS film. However, the TASVS-based film exhibits an asymmetric CIGS phase with a broad shoulder due to adverse phase separation of CuInSe2 and CuGaSe2. Through the use of the PASVS process, the improved film achieves uniform depth distribution of Ga through the CIGS film, resulting in a pure CIGS phase with moderate Ga concentration at the surface region. Results also indicate that the PASVS process causes more indium losses with the increase of selenization plasma power. From device performance point of view, the PASVS process and higher temperature pre-alloying treatment both are more feasible to yield an enhanced open circuit voltage and efficiency of the device.