Structural and electrical characterisation of MgCl2-treated CdTe solar cells

The impact of the back surface nitric-phosphoric (NP) acid etching treatment on CdTe solar cells following MgCl₂ activation treatment is investigated. A series of complete CdTe solar cells were produced with etching times in the 0-60 s range and compared via J-V analysis and SEM. Phases resulting from the treatment were observed via SEM analysis and shown to only be partially removed by NP etching for 60 s. Some of these residue phases contributed to high series resistance in un-etched cells. Analysis of J-V curve rollover showed the back contacting to be optimized following a 30 s NP etch, but this treatment did not correspond with that giving the highest efficiency devices. Further development to include 2 nm of Cu into the back contact allowed the formation of rollover-free contacts, with MgCl₂ treatment residues causing no negative effects.