Electrical properties of ZnO buffer layers and the performance of CdSeTe/CdTe solar cells

The electrical properties of as-deposited sputtered ZnO films with varying oxygen content in the Ar\O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> working gas have been investigated using an ultra-sensitive parallel dipole line (PDL) Hall effect system. Carrier concentration and mobility of the films have been extracted from the Hall effect measurements. Films deposited with below 0.5% oxygen in the Ar\O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> working gas have resulted in high carrier concentration on the order of 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm-<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>, whereas films with higher oxygen content were too resistive for measurement, suggesting a low carrier concentration below 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup>. ZnO films were used as a buffer layer in CdSeTe/CdTe devices, and the performance of complete devices was extracted from J-V measurements. Surprisingly, ZnO films with two extreme carrier concentrations did not lead to significant changes in device performance. The highest conversion efficiency was achieved with an as-deposited ZnO layer with low carrier concentration deposited with 0.5% oxygen in the Ar\O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> working gas.