An improved absorber tube (AT) design consisting of a semi-circular and an external flat fin with a flat plate radiation shield inside an evacuated annulus is proposed for large aperture parabolic trough concentrator (PTC) systems. In the present design, the AT's semi-circular part absorbs the most sun rays. The other rays originally absorbed by the AT's upper part is intercepted by the external two fins. The flat plate radiation shield reflects the external radiation energy from the AT's upper half back to the AT. The trough has an aperture of 8m and an 80 degrees half rim angle. The AT consists of a semicircle with a diameter of 100 mm and outer fins. The optical and thermal efficiency of this new design was up to 83.3% and 80.3%, respectively. The optical and thermal efficiency was 8%-units higher than that of the traditional optimal design. The maximum temperature always appears at the edge of the fin, which is up to 50 degrees C higher than that of the heat transfer fluid (HTF) at 0.5 m/s, which was the optimal fluid rate for the new design. The fins also contribute to the efficiency of the PTC: 6.5% to the optical and over 3.5% to the thermal efficiency. The improved AT design will help to plan more effective PTC systems. (C) 2020 Elsevier Ltd. All rights reserved.