The current status and future perspectives of Cu(In 1Àx Ga x )Se 2 (CIGS) solar cells and modules will be discussed in this paper. The conversion efficiencies of the state of the art laboratory-scale CIGS solar cells exceeded 20%, which are comparable to those of crystalline Si solar cells. The requirements on the properties of CIGS absorbers to achieve such high efficiencies will be described. The CIGS modules are already commercially available based on two major CIGS deposition techniques such as co-evaporation and selenization. The current status, problems, and prospects of co-evaporation and selenization will also be discussed. High-efficiency flexible CIGS solar cells with efficiencies similar to those fabricated on soda-lime glass (SLG) substrates have been achieved by developing a novel Na incorporation technique. Critical issues to demonstrate high-efficiency flexible solar cells will also be discussed.

The aim of the present contribution is to give a review on the recent work concerning Cd-free buffer and window layers in chalcopyrite solar cells using various deposition techniques as well as on their adaptation to chalcopyrite-type absorbers such as Cu(In,Ga)Se 2 , CuInS 2 , or Cu(In,Ga)(S,Se) 2 . The corresponding solar-cell performances, the expected technological problems, and current attempts for their commercialization will be discussed. The most important deposition techniques developed in this paper are chemical bath deposition, atomic layer deposition, ILGAR deposition, evaporation, and spray deposition. These deposition methods were employed essentially for buffers based on the following three materials: In 2 S 3 , ZnS, Zn 1 À x Mg x O.

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Dramatic improvement of current–voltage (I–V) performance, especially the fill factor (FF) observed in the Cu(InGa)Se2-based thin-film circuits with Zn(O, S, OH) x buffer after postdeposition light soaking is discussed in this study. Considering the composition of Zn(O, S, OH) x buffer and the reversible behavior with respect to postdeposition light soaking, a model is proposed, in which H2O molecules released by the dehydration of Zn(OH)2 in the Zn(O, S, OH) x buffer are considered to play a dominant role in this behavior. Based upon this model, attempts to stabilize the pn heterojunction by making the reversible behavior irreversible are, for the first time, successfully achieved by adjusting the postdeposition light-soaking conditions. The reduction of the Zn(OH)2 concentration in the Zn(O, S, OH) x buffer through the combination of heating at 130°C for at least 40 min and irradiation using a constant-light solar simulator contributes to stabilizing the pn heterojunction and improving the I–V performance as well as the electrical yield.