Stability of Cu(InxGa1-x)Se2 Solar Cells Utilizing RbF Postdeposition Treatment under a Sulfur Atmosphere

Alkali halide postdeposition treatments (PDTs) have become a key tool to maximize efficiency in Cu(InxGa1-x)Se-2 (CIGS) photovoltaics. RbF PDTs have emerged as an alternative to the more common Na- and K-based techniques. This study utilizes temperature-dependent current-voltage (JVT) measurements to study a unique RbF PDT performed in a S atmosphere. The samples are measured before and after 6 months in a desiccator to study device stability. Both samples contain Na and K which diffuse from the soda-lime glass substrate. A reference sample and a RbF + S PDT sample both show the development of a rear contact barrier after aging. The contact barrier is higher for the RbF + S PDT sample, leading to decreased current in forward bias. Series resistance is also higher in the RbF + S PDT device which leads to lower fill factor. However, after aging the reference sample has a larger decrease in open-circuit voltage (V-OC). Ideality factor measurements suggest Shockley-Read-Hall recombination dominates both samples. V-OC versus temperature and a temperature-dependent activation energy model are used to calculate diode activation energies for each sample condition. Both techniques produce similar values that indicate recombination primarily occurs within the bulk absorber.

Automated summary

Alkali halide postdeposition treatments (PDTs) are important for enhancing the efficiency of CIGS photovoltaics. RbF PDTs have emerged as an alternative to commonly used Na- and K-based techniques. This study investigates the effects of a unique RbF PDT performed in a S atmosphere using temperature-dependent current-voltage measurements. The results show that the RbF + S treated sample has a higher contact barrier and series resistance, resulting in decreased current and lower fill factor compared to the reference sample. However, the reference sample experiences a larger decrease in open-circuit voltage after aging.