Composition and bandgap control in Cu(In,Ga)Se sub(2)-based absorbers formed by reaction of metal precursors

The control of composition and bandgap in chalcopyrite thin-film absorber layers formed by a metal precursor reaction is addressed. Two processes using reaction with either H sub(2)Se or H sub(2)S as the final step of a three-step reaction process were compared as follows: a three-step H sub(2)Se/Ar/H sub(2)S reaction and a three-step H sub(2)Se/Ar/H sub(2)Se reaction. In both processes, significant Ga homogenization was obtained during the second-step Ar anneal, but the third-step selenization resulted in Ga depletion near the Cu(InGa)Se sub(2) surface, whereas the third-step sulfization did not. Solar cells were fabricated using absorbers formed using each method, and the surface Ga depletion significantly affected device performances. The solar cell incorporating the sulfization yielded a better device performance, with an efficiency of 14.4% (without an anti-reflection layer) and an open-circuit voltage of 609mV. The bandgap control in the metal precursor reaction is discussed in conjunction with the device behavior. Copyright copyright 2014 John Wiley & Sons, Ltd. In this work, we discuss composition and bandgap controls in CIGS-based absorbers by comparing two metal precursor reactions. A small difference in Ga composition near the top surface of an absorber was enough to significantly affect the activation energy for recombination determining V sub(OC). A general approach to bandgap designs using Ga and S contents in the metal precursor reaction was also presented.