(Ag,Cu)(In,Ga)Se2 thin films fabricated on flexible substrates via non-vacuum process

Abstract

(Ag,Cu)(In,Ga)Se2 thin films with various contents of silver ions were successfully fabricated on the stainless steel substrates using the non-vacuum spin-coating process. The solar cells with the stainless steel/Mo/ACIGS/CdS/i-ZnO/ITO structure were prepared. After selenization at 550 °C for 30 min, the monophasic chalcopyrite-structured (Ag,Cu)(In,Ga)Se2 thin films were formed. The conversion efficiency of (Ag,Cu)(In,Ga)Se2 solar cells was significantly increased from 4.34 to 6.29% when the molar ratio of Ag ions to total (Ag + Cu) ions was increased from 0 to 0.2. The increase in conversion efficiency was attributed to the liquid phase that was formed from (Ag,Cu)2In intermediate compound. The formed liquid phase facilitated the grain growth and promoted the densification of thin films. The densified thin films of (Ag,Cu)(In,Ga)Se2 suppressed the additional shunt path and decreased the value of shunt conductance (G) to 12.57 mS/cm2. In addition, the values of ideal factor (A), saturated current density (J0), and series resistance (Rs) were respectively decreased to 2.96, 0.08 mA/cm2, and 0.23 Ωcm2 due to suppressing the additional shunt path. When an excess of silver ions were doped into the CIGS thin films, the microstructures of the prepared thin films became porous, and the conversion efficiency of the solar cells was reduced. This research reveals that adding an appropriate amount of silver ions effectively improved the performance of (Ag,Cu)(In,Ga)Se2 solar cells.