CdTe thin films doped by Cu and Ag - a comparison in substrate configuration solar cells

One of the main problems to be solved in order to raise the efficiency of CdTe solar cells is the low acceptor concentration in polycrystalline CdTe layers which is limiting the open circuit voltage. The commonly used acceptor dopant Cu not only forms rather deep acceptor defects but is also likely to limit the net acceptor concentration due to the formation of compensating donor type defects. In this work, Ag is examined as a possible candidate for improving acceptor concentration in CdTe thin films. Hole density in CdTe layers with varying elemental Ag concentration follows a similar trend as previously reported for Cu doping. In finished solar cells efficiencies up to 11.6 % could be reached using Ag as acceptor dopant. Measurements of hole density, barrier height, space charge region width and depth dependent elemental distribution indicate the similarity of the Ag and Cu doping process.