Self-Assembled Monolayers of a Fluorinated Phosphonic Acid as a Protective Coating on Aluminum.

Aluminum (Al) placed in hot water (HW) at 90 °C is roughened due to its reaction with water, forming Al hydroxide and Al oxide, as well as releasing hydrogen gas. The roughened surface is thus hydrophilic and possesses a hugely increased surface area, which can be useful in applications requiring hydrophilicity and increased surface area, such as atmospheric moisture harvesting. On the other hand, when using HW to roughen specified areas of an Al substrate, ways to protect the other areas from HW attacks are necessary. We demonstrated that self-assembled monolayers (SAMs) of a fluorinated phosphonic acid (FPA, CF3(CF2)13(CH2)2P(=O)(OH)2) derivatized on the native oxide of an Al film protected the underneath metal substrate from HW attack. The intact wettability and surface morphology of FPA-derivatized Al subjected to HW treatment were examined using contact angle measurement, and scanning electron microscopy and atomic force microscopy, respectively. Moreover, the surface and interface chemistry of FPA-derivatized Al before and after HW treatment were investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS), verifying that the FPA SAMs were intact upon HW treatment. The ToF-SIMS results therefore explained, on the molecular level, why HW treatment did not affect the underneath Al at all. FPA derivatization is thus expected to be developed as a patterning method for the formation of hydrophilic and hydrophobic areas on Al when combined with HW treatment.

Study of Se/Te-doped Cu2O as a hole transport material in perovskite solar cells.

Theoretically, cuprous oxide (Cu2O) is a particularly excellent potential material, for the hole transport layer (HTL) of perovskite solar cells (PSCs). However, the photoelectric conversion efficiency (PCE) of its experimental samples is still not ideal. The main reasons for this include the material, and inherent and interface defects of Cu2O, but this can be improved by doping. In this research, Te- and Se/Te-doped Cu2O were experimentally and numerically studied to check the improvement of the material and interface properties. It was found that, for both the electrical and optical properties, the Se/Te-doped Cu2O performed considerably better than that which had been Te-doped and the pure Cu2O. Compared with the pure Cu2O thin film, the carrier mobility of the Se/Te-doped Cu2O thin film is improved from 60 cm2 V-1 s-1 to 1297 cm2 V-1 s-1, and the bandgap changed from 2.05 eV to 1.88 eV. According to the results calculated using solar cell simulation software SCAPS, the cell efficiency of the Se/Te-doped Cu2O is improved by 22% when compared to that of pure Cu2O. This efficiency can be further improved to 34% by optimizing the thickness of the Se/Te-doped Cu2O thin film and the defect density of states between the material interfaces.