A simple approach to ohmic contacts for transition metal dichalcogenide solar cells

Abstract

Transition metal dichalcogenide (TMDC) semiconductors are promising materials for the manufacture of ultrathin solar cells due to their optoelectronic properties and their potential for low-cost fabrication. However, they still present several technological challenges, such as the development of ohmic contacts. The most common contact technology is based on the deposition of metals on the TMDC and subsequent annealing. It is known that this process damages the crystalline structure of the TMDC, leading to Fermi level pinning at the contact interface (Schottky barrier). In this work we explore an easy-to-implement ohmic contact for TMDC solar cells, in which a very flat metal surface has been prepatterned on the substrate and the TMDC laminae are transferred onto it. The TMDC atomic layers remain intact, and they are joined to the metal surface only by van der Waals forces. If a metal of suitable working function is chosen, an ohmic contact is produced without the need of thermal annealing. Using the transfer length method (TLM) we demonstrate that it is possible to obtain contact resistances in the order of 1.10-3Ω. cm2 for n and p doped MoS2, which means that this simple fabrication method for van der Waals metal/TMDC contacts produces sufficiently low series resistance for one-sun applications.