Chemical bath deposited Zn(Se,OH)x on Cu(In,Ga)(S,Se)2 for high efficiency thin film solar cells: growth kinetics, electronic properties, device performance and loss analysis

Abstract

Zn(Se,OH)x thin films were grown on Cu(In,Ga)(S,Se)2 (CIGSS) substrate by chemical bath technique. The initial formation and subsequent development of the CIGSS/Zn(Se,OH)x interface are studied by XPS photoemission spectroscopy. Changes in the In 4d and Zn 3d core lines are used to directly determine the CIGSS/Zn(Se,OH)x heterojunction valence band discontinuity and the consequent heterojunction band diagram. For device optimization the thickness and good surface coverage were controlled by XPS-UPS photoemission spectroscopy. A Zn(Se,OH)x thickness below 10 nm has been found to be optimum for achieving a homogeneous and compact film on CIGSS. A remarkably high active area efficiency up to 15.7% (total area efficiency 13.26% with open circuit voltage (Voc) up to 565.74 mV, a fill factor (FF) of 71% and a short-circuit photocurrent density (Jph) greater than 33.01 mA/cm2) are obtained. The internal parameters, such as the saturation currents, the series resistance Rs and shunt resistance Rsh are calculated. Major losses in these cells are due to the significant influence of the series resistance Rs on the fill factor.