Cd-Free Cu(In,Ga)(Se,S)₂ Thin-Film Solar Cell With Record Efficiency of 23.35%

Abstract

In this article, the excellent properties of state-of-the-art Cd-free Cu(In,Ga)(Se,S) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (CIGSSe) solar cells with Zn(O,S,OH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> O double buffer layers, deposited by a combination of chemical bath deposition and atomic layer deposition techniques, are presented. By the replacement of conventional CdS buffer layers with this double buffer layer, the open-circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> ) deficit of the devices could be significantly reduced, and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> increased by approximately 15 mV. In addition, the fill factor and short-circuit current were also improved, increasing the device efficiency by approximately 0.5 absolute percent compared with devices with CdS buffers. The Cd-free double buffer layer improved the device efficiency regardless of the bandgap of the CIGSSe absorber. The minority carrier lifetime (τ) measured via time-resolved photoluminescence became longer, indicating that carrier recombination is mitigated using the double buffer layer. Based on the device parameters extracted by fitting the Suns-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> characteristics to the double-diode model, the longer τ could be attributed to the decreased recombination rate in the space-charge region, rather than in the bulk and at the interface. The best performing cell was evaluated by a reliable third party, the National Institute of Advanced Industrial Science and Technology; this cell achieved a new world record efficiency of 23.35% for 1-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -sized thin-film polycrystalline solar cells. The device parameters of this cell are also discussed in this article.

Keywords

Affiliated Institutions

• Idemitsu Kosan (Japan) JP

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