Physical manipulation of ultrathin-film optical interference for super absorption and two-dimensional heterojunction photoconversion**Project supported by the National Natural Science Foundation of China (Grant Nos. 61675142 and 61875143), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20140359), the Natural Science Research Project of the Higher Educational Institutions of Jiangsu Province, China (Grant No. 17KJA480004), the Postgraduate Research & Practice

Abstract

Ultrathin optical interference in a system composed of absorbing material and metal reflector has attracted extensive attention due to its potential application in realizing highly efficient optical absorption by using extremely thin semiconductor material. In this paper, we study the physics behind the high absorption of ultrathin film from the viewpoint of destructive interference and admittance matching, particularly addressing the phase evolution by light propagation and interface reflection. The physical manipulations of the ultrathin interference effect by controlling the substrate material and semiconductor material/thickness are examined. We introduce typical two-dimensional materials — i.e., MoS2 and WSe2 — as the absorbing layer with thickness below 10 nm, which exhibits ∼ 90% absorption in a large range of incident angle (0° ∼ 70°). According to the ultrathin interference mechanism, we propose the ultrathin (< 20 nm) MoS2/WSe2 heterojunction for photovoltaic application and carefully examine the detailed optoelectronic responses by coupled multiphysics simulation. By comparing the same cells on SiO2 substrate, both the short-circuit current density (up to 20 mA/cm2) and the photoelectric conversion efficiency (up to 9.5%) are found to be increased by ∼ 200%.