Stability Issues of Cu(In,Ga)Se₂-Based Solar Cells

Abstract

Stability aspects of the Mo/Cu(In,Ga)Se 2 /CdS/ZnO solar cell are reviewed and assessed. These include (i) the chemical stability of the various interfaces present in the device, (ii) the long-term behavior of metastable defects found in the Cu(In,Ga)Se 2 (CIGS) compound, and (iii) the impact of Cu migration on device performance and lifetime. We find that (i) all interfaces within the structure are chemically stable, (ii) metastable defects have a beneficial effect on performance, and (iii) Cu migration effects are reversible and their possible detrimental effects are eclipsed by the beneficial effect of the metastable states. Moreover, Cu out-diffusion from the CIGS layer is absent in photovoltaic-quality CIGS. Finally, we propose a model that explains the exceptional radiation hardness and impurity tolerance of CIGS-based devices, based on the synergetic effect of copper migration and point defect reactions.

Anion vacancies as a source of persistent photoconductivity in II-VI and chalcopyrite semiconductors

“…Specifically, we predict that the oxygen vacancy V O leads to persistent electron photoconductivity (n-type PPC) in n-ZnO observed recently after proton irradiation [18], whereas the Se vacancy V Se causes persistent hole photoconductivity (p-type PPC) in p-CuInSe 2 or p-CuGaSe 2 , constituting the unusual case where a donor-like defect causes p-type PPC. Thus, our results shed new light on hitherto unknown physical origin of the phenomenon of light-induced metastability in chalcopyrite CuInSe 2 based photovoltaic devices exhibiting p-type PPC [19,20,21,22,23]. Here, this light-induced effect leads to performance enhancement [19,21,23], in stark contrast to "light-induced degradation" of other solar cells, e.g.…”

“…Thus, our results shed new light on hitherto unknown physical origin of the phenomenon of light-induced metastability in chalcopyrite CuInSe 2 based photovoltaic devices exhibiting p-type PPC [19,20,21,22,23]. Here, this light-induced effect leads to performance enhancement [19,21,23], in stark contrast to "light-induced degradation" of other solar cells, e.g. Staebler-Wronski degradation in a-Si [24].…”

“…Note that the initial ionized charge state here is different from the initial neutral state required in ZnO. Illumination [19,20,21,22,23] or electron injection [68] of such CuInSe [69]. Immediately after the optical excitation, the electron in the state occupies the shallow PHS rather than the DLS (viz.…”

Defect Spectroscopy on Damp-Heat Treated ZnO/CdS/Cu(In,Ga)(S,Se)2/Mo Heterojunction Solar Cells

“…In particular, the influence of water vapor and oxygen on the charge transport properties of the heterostructure 0932-0784 / 03 / 1200-0691 $ 06.00 c 2003 Verlag der Zeitschrift für Naturforschung, Tübingen · http://znaturforsch.com cells is the focus of our paper. Oxygen-related phenomena have been discussed in the literature for more than a decade [6], and extensive work covering oxygenation [7] and related topics [8] is available. The impact of water vapor on the cell characteristics goes beyond the magnitude of the influence of oxygen [9], even though both effects are closely related to each other.…”

Solar cells on CMOS chips as energy harvesters : integration and CMOS compatibility

“…The efficiency at indoor light is reportedly larger than 5% [23,105]. Last but not least, very good long-term reliability and radiation hardness are further reported for this type of thin-film solar cell [182].…”