Investigation of the effect of I-ZnO window layer on the device performance of the Cd-free CIGS based solar cells

Cu(In,Ga)Se2 (CIGS) thin films were deposited on Molybdenum coated soda lime glass (SLG/Mo) substrates, using physical vapor deposition (PVD) 3-stage process. The CIGS films were treated by ammonium hydroxide solution before depositing the I-ZnO buffer layer. The I-ZnO layer was deposited using metallorganic chemical vapor deposition (MOCVD) at different substrate temperatures of 200°C, 250°C, and 300°C. The thickness of this buffer layer was varied according to the location of the substrates with respect to the gas flow direction. The CIGS devices were completed by depositing the Al-ZnO window layer by rf magnetron sputtering and applying the Ni/Al front contact grids. The thickness of the I-ZnO buffer layer was measured using a Dek-tak profilometer on soda lime glass substrates which were used as reference samples during the deposition process of I-ZnO buffer layer on CIGS films. Surface depth profiling survey for the elements and their chemical states, as well as their relative concentration was analyzed by X-Ray Photoelectron Spectroscopy (XPS) for as deposited and ammonium hydroxide treated CIGS films. In addition, the performance of the completed CIGS devices was evaluated under standard conditions of 1000 W/m² and 25°C.