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 1nm. 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.