An investigation on copper doping to CdTe absorber layers in CdTe thin film solar cells

Abstract

Polycrystalline Cadmium Telluride (CdTe) is the most stable compound that melts congruently. This leads to the feasibility of multiple methods of deposition, which consistently produce stoichiometric thin film CdTe. On the other hand, this has become a disadvantage of CdTe due to the tendency of self-compensation and limiting the doping capability hence limiting the improvement of solar cells efficiency and open-circuit voltage. AMPS 1D simulation of CdTe conventional device structure indicates significant open-circuit voltage improvement with effective acceptor concentration >1015 cm−3. Copper has been utilized commonly as p-type dopant in the R&D of CdTe thin film solar cells. In this work, different copper concentration were examined and introduced to CdTe thin film absorbers. Controlled amount of Cu were applied in solution form prior to the back contact formation process. The solar cells efficiency and open-circuit voltage indicate that doping of Cu in CdTe has an optimum range that limits the effective acceptor concentration. Exceeding the optimum concentration has adverse impact to efficiency and open-circuit voltage due to self-compensation. Short-circuit current density and fill factor saturates at high Cu concentration. This suggests that the method of Cu doping application through CdTe thin film surface has a saturation level.