Abstract
The aim of this thesis is to provide systematic exploration of the photovoltaic characteristics in most popular 2D materials (graphene, MoS2, and WSe2) in recent years for designing devices compatible with conventional materials (such as Si) to expand the opportunity for mass production in the future semiconductor and energy industries. In this thesis, the fabrication and characterization of 2D material based photovoltaic devices including MoS2/Si heterojunction, graphene quantum dot in hybrid solar cells, and MoS2/WSe2 lateral heterojunction have been achieved for developing the nanoscale energy applications for the next generation. We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photo-generated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%. By employing graphene quantum dots in PEDOT:PSS, we have accomplished the efficiency of 13.22% in Si/PEDOT:PSS hybrid solar cells. The efficiency enhancement is based on concurrent improvement in optical and electrical properties by the photon downconversion process and the improved conductivity of PEDOT:PSS. The short circuit current and the fill factor are increased from 32.11 to 36.26 mA/cm2 and 62.85% to 63.87%, respectively. Finally, electrical and optical properties of lateral monolayer WSe2-MoS2 p-n heterojunction were characterized to demonstrate a high responsivity of 0.26 A/W with excellent omnidirectional photodetection capability. The heterojunction functioning as a diode exhibits prominent gate-tuning behavior with an ideality factor of 1.25. In addition, ultrafast photoresponse, low-light detectability, and high-temperature operation have been achieved.