Hydrothermally Grown TiO2 Nanorod Array Memristors with Volatile States
2020-05-20, Ebenhoch, Carola, Kalb, Julian, Lim, Joohyun, Seewald, Tobias, Scheu, Christina, Schmidt-Mende, Lukas
In the present study, the memristive characteristics of hydrothermally grown TiO2 nanorod arrays, particularly, the difference in the retention-time of the resistance state are investigated in dependence of the array growth temperature. A volatile behavior is observed and related to a redistribution of oxygen vacancies over time. It is shown, that the retention time increases for increasing array growth temperatures from several seconds up to 20 minutes. The relaxation behavior is also seen in the current-voltage characteristics, which do not show the common unipolar, bipolar, or complementary switching behavior. Instead, the temporal evolution depends on the duration of the applied voltage and on the nanowire growth temperature. Therefore, electronic measurements are combined with scanning electron and scanning transmission electron microscopy, so that the amount of oxygen defect-rich grain boundaries in the upper part of the nanowires can be linked to the differences in the current-voltage behavior and retention time.
Improving pore-filling in TiO2 nanorods and nanotubes scaffolds for perovskite solar cells via methylamine gas healing
2018-08, Nawaz, Asmat, Wong, Ka Kan, Ebenhoch, Carola, Zimmermann, Eugen, Zheng, Zhaoke, Akram, Muhammad Nadeem, Kalb, Julian, Wang, Kaiying, Fakharuddin, Azhar, Schmidt-Mende, Lukas
High performance in perovskite solar cells is often achieved using compact metal oxide layers or their mesoporous analogues. One dimensional scaffold materials such as nanorods or nanotubes are also employed in order to improve charge collection, however, perovskite pore-filling in these nanostructures is rather low. Herein, we introduce a method to more efficiently fill the pores in two most common nanostructure architectures namely, TiO2 nanorods and nanotubes. The method employs recrystallization of perovskite films in a methylamine rich environment– the so called perovskite healing. Whereas the scanning electron microscopy imaging revealed an improved pore-filling and formation of large perovskite grains upon healing, the complementary photoluminescence and electrical characterizations revealed improved charge transfer in the healed films than their pristine rivals. We also report a notable improvement in photoconversion efficiency and a better stability under continuous light soaking in the healed perovskite films.