Film formation from plasma-enabled surface-catalyzed dehalogenative coupling of a small organic molecule.

This work demonstrates a new pathway to the direct on-surface fabrication of surface coatings by showing that application of a plasma can lead to dehalogenative coupling of small aromatic molecules at a catalytic surface. Specifically, we show that a room temperature, atmospheric pressure plasma can be used to fabricate a coating through a surface-confined dehalogenation reaction. Plasma treatments were performed using a dielectric barrier discharge (DBD) technique under pure nitrogen with a variety of power levels and durations. Samples were analysed by optical and helium ion microscopy (HIM), X-ray photoelectron spectroscopy (XPS), optical profilometry, and contact angle measurement. By varying the plasma parameters we could control the chemistry, morphology and roughness of the film. Surface wettability also varied with the plasma parameters, with high-dose plasmas leading to a hydrophobic surface with water contact angles up to 130°.

Tuning the Amount of Oxygen Vacancies in Sputter-Deposited SnOx films for Enhancing the Performance of Perovskite Solar Cells.

This work demonstrates the effect of oxygen vacancies in SnOx thin films on the performance of perovskite solar cells. Various SnOx films with different amounts of oxygen vacancies were deposited by sputtering at different substrate temperatures (25-300 °C). The transmittance of the films decreased from 82 to 66 % with increasing deposition temperature from 25 to 300 °C. Both X-ray photoelectron spectroscopy and electron-spin resonance spectroscopy confirmed that a higher density of oxygen vacancies was created within the SnOx film at a high substrate temperature, which caused narrowing of the SnOx bandgap from 4.1 (25 °C) to 3.74 eV (250 °C). Combined ultraviolet photoelectron spectroscopy and UV/Vis spectroscopy showed an excellent conduction band position alignment between the methylammonium lead iodide perovskite layer (3.90 eV) and the SnOx electron transport layer deposited at 250 °C (3.92 eV). As a result, a significant enhancement of the open-circuit voltage from 0.82 to 1.0 V was achieved, resulting in an increase of the power conversion efficiency of the perovskite solar cells from 11 to 14 %. This research demonstrated a facile approach for controlling the amount of oxygen vacancies in SnOx thin films to achieve a desirable energy alignment with the perovskite absorber layer for enhanced device performance.