Trigonal-Tellurium (t-Te) has recently garnered interest in the nanoelectronics community because of its measured high hole mobility and low-temperature growth. However, a drawback of tellurium is its small bulk bandgap (0.33 eV), giving rise to large leakage currents in transistor prototypes. We analyze the increase of the electronic bandgap due to quantum confinement and compare the relative stability of various t-Te nanostructures (t-Te nanowires and layers of t-Te) using first-principles simulations. We found that small t-Te nanowires (≤4 nm2) and few-layer t-Te (≤3 layers) have bandgaps exceeding 1 eV, making Tellurium a very suitable channel material for extremely scaled transistors, a regime where comparably sized silicon has a bandgap that exceeds 4 eV. Through investigations of structural stability, we found that t-Te nanowires preferentially form instead of layers of t-Te since nanowires have a greater number of van der Waals (vdW) interactions between the t-Te-helices. We develop a simplified picture of structural stability relying only on the number of vdW interactions, enabling the prediction of the formation energy of any t-Te nanostructure. Our analysis shows that t-Te has distinct advantages over silicon in extremely scaled nanowire transistors in terms of bandgap and the t-Te vdW bonds form a natural nanowire termination, avoiding issues with passivation.

The impact of device architecture on organic photovoltaic device performance has been problematic to quantify due to extraction layer materials and device testing issues. In particular, published reports have used different pairs of hole and electron extraction layer materials for conventional versus inverted devices. The origins of the large apparent discrepancy in device J-V characteristics become difficult to understand, arising from differences in built-in potentials and in the extraction layers' conductivities that can affect collection of stray current outside of device

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Although cyclic voltammetry (CV) measurements in solution have been widely used to determine the highest occupied molecular orbital energy (EHOMO) of semiconducting organic molecules, an understanding of the experimentally observed discrepancies due to the solvent used is lacking. To explain these differences, we investigate the solvent effects on EHOMO by combining density functional theory and molecular dynamics calculations for four donor molecules with a common backbone moiety. We compare the experimental EHOMO values to the calculated values obtained from either implicit or first solvation shell theories. We find that the first solvation shell method can capture the EHOMO variation arising from the functional groups in solution, unlike the implicit method. We further applied the first solvation shell method to other semiconducting organic molecules measured in solutions for different solvents. We find that the EHOMO obtained using an implicit method is insensitive to solvent choice. The first solvation shell, however, produces EHOMO values that are sensitive to solvent choices and agrees with published experimental results. The solvent sensitivity arises from a hierarchy of three effects: (1) the solute electronic state within a surrounding dielectric continuum, (2) ambient temperature or solvent atoms changing the solute geometry, and (3) electronic interactions between the solute and solvents. The implicit method, on the other hand, only captures the effect of a dielectric environment. Our findings suggest that EHOMO obtained by CV measurements should account for the influence of solvent when the results are reported, interpreted, or compared to other molecules.