Composition and bandgap control in Cu(In,Ga)Se2‐based absorbers formed by reaction of metal precursors

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Composition and bandgap control in Cu(In,Ga)Se2‐based absorbers formed by reaction of metal precursors

Kim, Kihwan

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 2 Se or H 2 S as the final step of a three‐step reaction process were compared as follows: a three‐step H 2 Se/Ar/H 2 S reaction and a three‐step H 2 Se/Ar/H 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 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 609 mV. The bandgap control in the metal precursor reaction is discussed in conjunction with the device behavior. 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 OC . A general approach to bandgap designs using Ga and S contents in the metal precursor reaction was also presented.