Copper Doped Window Layer for CdSe Solar Cells

CdSe solar cells with ZnTe as the window layer deposited by CSS process have shown Voc\u27s around 630mV. However the currents were very low and also the voltages were not meeting the desired objectives. To improve the performance the contact energy at the ZnTe/Cu interface should be minimized by doping the window layer. Thermal evaporation was used to deposit ZnTe to have more control over the composition of the film. Initial experiments were done by depositing Cu doped ZnTe films on plain glass by co-evaporating both ZnTe and Cu. The conductivity was in the order of 10e3 which shows copper present in the film in the order of 1e22 S/cm³. This accomplishes a tunneling contact with the top electrode. Using the ZnTe:Cu contacts in complete devices resulted in disappointing voltages and currents. Efforts were made to deal with the poor performance of the cells. Devices were made on different types of TCO coated glass substrates but, were resulting in the same numbers which shows the type of TCO has an insignificant effect on the performance. The Cu doping has been helping in raising the Vocs but at the same time marred the currents whose effect has been unexplainable. Further experiments have been made changing the ZnTe thickness and concentration of Cu doping. Experiments were done increasing the substrate temperature as high as 5000C during ZnTe deposition and a Se flux has been introduced so as to compensate the loss of Se from CdSe at such high substrate temperature. But these experiments resulted in dismal performance indicating the domination of defects in the undoped ZnTe layer