Effect of Ordered Vacancy Compounds on the Carrier Collection in Wide‐Gap (Ag,Cu)(In,Ga)Se2 Solar Cells

Abstract

This contribution studies the effect of ordered vacancy compounds (OVCs) on the minority carrier collection in wide‐gap (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells. For this purpose, three samples with different ([Ag]+[Cu])/([In]+[Ga]) (I/III) values were processed: 1) a very off‐stoichiometric absorber (I/III = 0.31), consisting of isolated chalcopyrite patches embedded in a major OVC bulk phase, 2) a moderately off‐stoichiometric absorber (I/III = 0.77) with OVC patches at the front and back interfaces and 3) a close‐stoichiometric absorber (I/III = 0.94) with only very few, isolated OVC patches. For each of these samples, synchrotron‐based X‐ray fluorescence (XRF) was measured on a nanoscale (55 nm resolution), while simultaneously recording the X‐ray beam induced current (XBIC). The results, complemented by transmission electron microscopy and electron‐beam induced current analyses, clearly indicate that the presence of the OVC phase reduces the carrier collection and thus the short‐circuit current density of off‐stoichiometric wide‐gap ACIGS solar cells.