[en] Junctions between two dissimilar materials have been a topic of significant research interest due to novel interface physics and its direct importance on device performance due to the influence of defect states, structural and electronic discontinuities. Due to atomically thin semiconductor layer in 2D-3D semiconductors, investigating and understanding the nature of interface and its influence on the device characteristics becomes even more complex and intriguing. In this presentation, the influence of 2D-3D interfaces on the device characteristics of G-Si solar cell, MoS₂-ZnS intermediate band gap semiconductor and MoS₂-Bi₂Te₃ thermoelectric devices will be discussed. In the first example, graphene layers prepared by CVD method have been used as a top layer in p-n silicon junctions and an increase in efficiency from 5.3% to 8.9% is observed. Surface potential changes at the graphene -Si junctions in surface and junction modes have been examined using Kelvin probe force microscopy investigations. Voc nanoscale maps derived from these measurements show that topographical impurities and wrinkled boundaries on the graphene surface affecting junction performance. In another study, patterned MoS₂ 2D layers having feature size varying from 10 um to 1 um have been grown by a combination of stencil lithography and magnetron sputtering technique. Composite layers having wide band gap ZnS films and 2D MoS₂ layers show increased interface voltage due to 2D character. In the third example, the influence of n-n and n-p interfaces in MoS₂-Bi₂Te₃ and MoS₂-Sb₂Te₃ devices on the electron and phonon scattering resulting in improved thermoelectric properties will be discussed. The methodology described in this presentation can be extended to other junction devices. (author)