Implications of conductive grain boundaries in Chlorine-treated CdTe solar cells

The rear surfaces of CdTe photovoltaic devices without back contacts, grown by closed-space sublimation (CSS) were analyzed using conductive - atomic force microscopy (CAFM). As-deposited and CdCl
₂
treated CdTe samples were compared to clarify the effect of the treatment on charge flow through grains and grain boundaries. The CdCl
₂
treated samples exhibit a more homogenous and enhanced current flow across the grains as compared to the as-deposited samples. Under high bias, grain boundaries dominate current flow when the main junction is reverse biased and conducting current in reverse breakdown. The results are interpreted as resulting from the improved crystallinity of the CdTe with reduced p-type doping along the grain boundaries. Further, implications of these grain boundaries and guidelines for optimal device microstructure are discussed.