Atomic layer deposition of Zn1-xMgxO buffer layers for Cu(In,Ga)Se2 solar cells

Fabrication of Zn1-xMgxO films by atomic layer deposition (AID) has been studied for use as buffer layers in Cu(InGa)Se-2 (CIGS)-based solar cell devices. The Zn1-xMgxO films were grown using diethyl zinc, bis-cyclopentadienyl magnesium and water as precursors in the temperature range from 105 to 180 degrees C. Single-phase ZnO-like films were obtained for x < 0.2, followed by a two phase region of ZnO- and MgO-like structures for higher Mg concentrations. Increasing optical band gaps of up to above 3.8 eV were obtained for Zn1-xMgxO with increasing x. It was found that the composition of the Zn1-xMgxO films varied as an effect of deposition temperature as well as by increasing the relative amount of magnesium precursor pulses during film growth. Completely Cd-free CIGS-based solar cells devices with ALD-Zn1-xMgxO buffer layers were fabricated and showed efficiencies of up to 14.1%, which was higher than that of the CdS references. Copyright (c) 2006 John Wiley & Sons, Ltd.