@article{al shafe_schrickx_ding_ade_brendan t. o'connor_2023, title={Rubber-Toughened Organic Solar Cells: Miscibility-Morphology-Performance Relations}, volume={8}, ISSN={["2380-8195"]}, DOI={10.1021/acsenergylett.3c01124}, abstractNote={Tough organic solar cell (OSC) active layers are necessary to achieve robust, flexible, and stretchable devices. A major challenge is that the brittle small molecule acceptor (SMA) in polymer/SMA bulk heterojunctions results in films prone to mechanical failure. To improve mechanical toughness, we investigate the use of a thermoplastic elastomer (styrene-b-ethylene-butylene-styrene) (SEBS) as an additive in high-performance photoactive layers. We find a consistent transition of all measured parameters [e.g., fracture energy (Gc) and power conversion efficiency (PCE)] at a SEBS concentration of 5–10 wt %, which is driven by the miscibility of the SEBS. We use this insight to optimize the SEBS loading for PCE and toughness. Optimized OSCs are found to increase Gc significantly with a marginal decrease in PCE, resulting in a record Gc·PCE metric, considering all OSC photoactive layers. The pronounced miscibility–function relationship provides a framework to optimize elastomer addition in OSCs for performance and toughness.}, journal={ACS ENERGY LETTERS}, author={Al Shafe, Abdullah and Schrickx, Harry M. and Ding, Kan and Ade, Harald and Brendan T. O'Connor}, year={2023}, month={Aug} }
 @article{booth_khanna_schrickx_siddika_al shafe_brendan t. o'connor_2022, title={Electrothermally Actuated Semitransparent Shape Memory Polymer Composite with Application as a Wearable Touch Sensor}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.2c10290}, abstractNote={A semitransparent shape memory polymer (SMP):silver nanowire (AgNW) composite is demonstrated to be capable of low-temperature actuation, thus making it attractive for wearable electronics applications that require intimate contact with the human body. We demonstrate that the SMP:AgNW composite has tunable electrical and optical transparency through variation of the AgNW loading and that the AgNW loading did not significantly change the mechanical behavior of the SMP. The SMP composite is also capable of electrical actuation through Joule heating, where applying a 4 V bias across the AgNWs resulted in full shape recovery. The SMP was found to have high strain sensitivity at both small (<1%) and large (over 10%) applied strain. The SMP could sense strains as low as 0.6% with a gauge factor of 8.2. The SMP composite was then utilized as a touch sensor, able to sense and differentiate tapping and pressing. Finally, the composite was applied as a wearable ring that was thermally actuated to conformably fit onto a finger as a touch sensor. The ring sensor was able to sense finger tapping, pressing, and bending with high signal-to-noise ratios. These results demonstrate that SMP:AgNW composites are a promising design approach for application in wearable electronics.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Booth, Ronald E. and Khanna, Chetna and Schrickx, Harry M. and Siddika, Salma and Al Shafe, Abdullah and Brendan T. O'Connor}, year={2022}, month={Nov} }
 @article{al-tawhid_shafe_bagheri_guan_reddy_mita_moody_collazo_sitar_ahadi_2021, title={Weak localization and dimensional crossover in compositionally graded AlxGa1-xN}, volume={118}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0042098}, DOI={10.1063/5.0042098}, abstractNote={The interaction between the itinerant carriers, lattice dynamics, and defects is a problem of long-standing fundamental interest for developing quantum theory of transport. Here, we study this interaction in the compositionally and strain-graded AlGaN heterostructures grown on AlN substrates. The results provide direct evidence that a dimensional crossover (2D–3D) occurs with increasing temperature as the dephasing scattering events reduce the coherence length. These heterostructures show a robust polarization-induced 3D electron gas and a metallic-like behavior down to liquid helium temperature. Using magnetoresistance measurements, we analyze the evolution of the interaction between charge carriers, lattice dynamics, and defects as a function of temperature. A negative longitudinal magnetoresistance emerges at low temperatures, in line with the theory of weak localization. A weak localization fit to near zero-field magneto-conductance indicates a coherence length that is larger than the elastic mean free path and film thickness (lφ>t>lel), suggesting a 2D weak localization in a three-dimensional electron gas. Our observations allow for a clear and detailed picture of two distinct localization mechanisms that affect carrier transport at low temperature.}, number={8}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Al-Tawhid, Athby and Shafe, Abdullah-Al and Bagheri, Pegah and Guan, Yan and Reddy, Pramod and Mita, Seiji and Moody, Baxter and Collazo, Ramon and Sitar, Zlatko and Ahadi, Kaveh}, year={2021}, month={Feb} }