Chalcopyrite Thin-Film Tandem Solar Cells with 1.5 V Open-Circuit-Voltage

Abstract

We have fabricated two-terminal mechanical stacked chalcopyrite-based tandem devices to identify the technical issues required to achieve high performance solar cells in the near future. A tandem device with a Ag(ln <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> )Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (AIGS) top cell and a Cu(ln,Ga)Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (CIGS) bottom cell showed an open-circuit-voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> ) of 1.46 V. It was, however, found that the short-circuit current (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> ) of a two-terminal tandem device was limited by the low J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> of the filtered bottom cell because of a current mismatch between the top and bottom cells. In order to improve the Jsc of the filtered bottom cell, we have tried two process options, replacing ITO back contacts with high-mobility (Mo-doped ln <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) IMO and the use of low-Ga content CIGS bottom cells. The J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> of the filtered bottom cells increased significantly using these techniques. As a result, an 8 % total-area (0.5 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) efficiency 2-terminal mechanical stacked tandem device was achieved using a CIGS (15% Ga) bottom cell with an AIGS top cell fabricated with an IMO back contact