2023, Bai, Shaoling, Yang, Lin, Haase, Katherina, Wolansky, Jakob, Zhang, Zongbao, Tseng, Hsin, Talnack, Felix, Kress, Joshua, Andrade, Jonathan Perez, Benduhn, Johannes, Ma, Ji, Feng, Xinliang, Hambsch, Mike, Mannsfeld, Stefan C. B.

Organic phototransistors can enable many important applications such as nonvolatile memory, artificial synapses, and photodetectors in next-generation optical communication and wearable electronics. However, it is still a challenge to achieve a big memory window (threshold voltage response ∆V ) for phototransistors. Here, a nanographene-based heterojunction phototransistor memory with large ∆V responses is reported. Exposure to low intensity light (25.7 µW cm ) for 1 s yields a memory window of 35 V, and the threshold voltage shift is found to be larger than 140 V under continuous light illumination. The device exhibits both good photosensitivity (3.6 × 10 ) and memory properties including long retention time (>1.5 × 10  s), large hysteresis (45.35 V), and high endurance for voltage-erasing and light-programming. These findings demonstrate the high application potential of nanographenes in the field of optoelectronics. In addition, the working principle of these hybrid nanographene-organic structured heterojunction phototransistor memory devices is described which provides new insight into the design of high-performance organic phototransistor devices.

2023, Rao, Shraddha M., Kiligaridis, Alexander, Yangui, Aymen, An, Qingzhi, Vaynzof, Yana, Scheblykin, Ivan G.

Defects in metal halide perovskites (MHP) are photosensitive, making the observer effect unavoidable when laser spectroscopy methods are applied. Photoluminescence (PL) bleaching and enhancement under light soaking and recovery in dark are examples of the transient phenomena that are consequent to the creation and healing of defects. Depending on the initial sample composition, environment, and other factors, the defect nature and evolution can strongly vary, making spectroscopic data analysis prone to misinterpretations. Herein, the use of an automatically acquired dependence of PL quantum yield (PLQY) on the laser pulse repetition rate and pulse fluence as a unique fingerprint of both charge carrier dynamics and defect evolution is demonstrated. A simple visual comparison of such fingerprints allows for assessment of similarities and differences between MHP samples. The study illustrates this by examining methylammonium lead triiodide (MAPbI3) films with altered stoichiometry that just after preparation showed very pronounced defect dynamics at time scale from milliseconds to seconds, clearly distorting the PLQY fingerprint. Upon weeks of storage, the sample fingerprints evolve toward the standard stoichiometric MAPbI3 in terms of both charge carrier dynamics and defect stability. Automatic PLQY mapping can be used as a universal method for assessment of perovskite sample quality.

2019, Elsmann, Tino, Becker, Martin, Olusoji, Olugbenga, Unger, Sonja, Wondraczek, Katrin, Aichele, Claudia, Lindner, Florian, Schwuchow, Anka, Nold, Johannes, Rothhardt, Manfred

The photosensitivity of various cerium-doped fibers has been experimentally investigated for both excimer- and femtosecond-laser illumination. The results of single-pulse, few-pulse and multi-pulse inscription of fiber-Bragg-gratings with both laser systems and the thermal aging of those gratings demonstrated the restrictions of the conventional color center model for cerium-doped fibers. To explain the short-term stability of single-pulse gratings against long-term stability of multi-pulse gratings, an extension into a two-step-model was deduced.