Atomic layer deposition of Zn_1−xMg_xO buffer layers for Cu(In,Ga)Se₂ solar cells

Abstract

Abstract Fabrication of Zn 1−x Mg x O films by atomic layer deposition (ALD) has been studied for use as buffer layers in Cu(In,Ga)Se 2 (CIGS)‐based solar cell devices. The Zn 1−x Mg x O films were grown using diethyl zinc, bis‐cyclopentadienyl magnesium and water as precursors in the temperature range from 105 to 180°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 Zn 1−x Mg x O with increasing x. It was found that the composition of the Zn 1−x Mg x O 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‐Zn 1−x Mg x O buffer layers were fabricated and showed efficiencies of up to 14·1%, which was higher than that of the CdS references. Copyright © 2006 John Wiley & Sons, Ltd.