Electrical properties of the CdTe back contact: A new chemically etching process based on nitric acid/acetic acid mixtures

The performance of the back contact is one of the major issues of CdTe solar cell research. Standard nitric-phosphoric (NP) acid chemical etching before metallization is widely used to improve contact formation. However, previous studies of this traditional etching method indicated a blocking Schottky barrier at the back contact, and a roll-over phenomenon was found in the J-V curves of the CdTe solar cells. In this work, a new etching solution, i.e. a nitric-acetic (NA) acid was employed. The etching rate was slow and a Te-rich layer was formed on the surface, which was less than 1 nm. The CdTe solar cell with this new etching method showed no roll-over phenomenon and displayed a good ohmic back contact performance. XPS analysis demonstrated that the back contact barrier height was close to those of CdTe with standard NP etching. A possible mechanism was presented for the improvement of back contact properties.