SPLTRAK Abstract Submission
Effects of Novel In+RbF Post-Deposition Treatment on Cu(InxGa1-x)Se2 Solar Cells
Jake Wands1, Polyxeni Tsoulka2, Thomas Lepetit2, Nicolas Barreau2, Angus Rockett1
1Colorado School of Mines, Golden, CO, United States
/2Universite de Nantes, Nantes, France

Alkali halide post-deposition treatments (PDT) have been a critical technique in helping Cu(InxGa1-x)Se2 (CIGS) solar cells become a leading thin-film technology. While sodium and potassium based treatments have traditionally received most of the research focus, RbF has gained popularity in recent years. In this study the effects of a novel PDT using In+RbF co-evaporation are investigated and compared with as-deposited and RbF treated devices.
Temperature dependent current-voltage measurements were used to characterize the recombination mechanics of each device. Open circuit voltage (VOC) was measured to be 643mV for the as-deposited device, 593mV after RbF PDT, and 698mV after In+RbF PDT. The diode activation energy was determined by extrapolation of the VOC vs temperature plots to 0 K for all three devices. Each device has an activation energy approximately equal to the bandgap, which suggests recombination is dominated by states in the bulk absorber rather than at interfaces. The RbF PDT had increased reverse saturation current density (J0) compared to the as-deposited sample indicating an increased recombination rate. However, the In+RbF PDT had significantly lower J0 suggesting that the addition of In reduced recombination. The ideality factor for the as-deposited and In+RbF PDT samples is near 1.6, which is typically thought to be associated with Shockley-Read-Hall recombination through sub-bandgap defects. In the RbF PDT sample the ideality factor is much higher near 2.5 which could be a sign of tunneling recombination playing a role.