PEDOT:PSS as back contact for CdTe solar cells and the effect of PEDOT:PSS conductivity on device performance

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was studied as the back contact of Cadmium telluride (CdTe) solar cells and was compared with conventional Cu-based back contact. A series of PEDOT:PSS aqueous solutions with different conductivities were spin coated onto the glass/SnO2:F/SnO2/CdS/CdTe structures as back contact, and the PEDOT:PSS conductivity dependence of device performance was studied. It was found that PEDOT:PSS back contact with higher conductivity produces devices with lower series resistance and higher shunt resistance, leading to higher fill factor and higher device efficiencies. As the conductivity of PEDOT:PSS increased from 0.03 to 0.24 S/cm, the efficiency of the solar cell increased from 2.7 to 5.1 %. Methanol cleaning also played an important role in increasing the device performance. The efficiency of our best device with PEDOT:PSS back contact has reached 9.1 %, approaching those with conventional Cu/Au back contact (12.5 %).