Impact of RbF Postdeposition Treatment Dose on Defects and the Barrier at the Back Contact in (Ag, Cu)(In, Ga)Se 2 Solar Cells

The impact of RbF postdeposition treatment, including the influence of the total RbF dose, on bulk defects and the back contact barrier in (Ag, Cu)(In, Ga)Se 2 (ACIGS) solar cells is investigated. Deep level transient spectroscopy (DLTS) reveals three signatures: H1, H2, and N1. H1 and H2 are attributed to hole traps within the material bulk, and N1 is attributed to the back contact barrier. The H2 trap acts as a recombination center and is found to affect the room temperature capacitance–voltage ( C – V ) results, necessitating “fast C – V ” measurements. The N1 signature has increasing activation energy (barrier height) with increasing RbF dose, and good quantitative agreement is obtained between energies measured using DLTS and admittance spectroscopy, as well as qualitative agreement with current–voltage–temperature ( J – V – T ) measurements. Macroscale SIMS and nanoscale transmission electron microscopy‐based X‐ray energy dispersive spectroscopy measurements reveal Rb accumulation at the ACIGS/MoSe 2 interface that increases, along with Rb concentration in the ACIGS bulk, with increasing RbF dose. The accumulation of compensating charges near this interface is proposed to be the explanation for the increased back contact barrier height observed here.