UROP Proceedings 2020-21

School of Science Department of Physics 73 Stability Analysis in General Relativity Supervisor: WANG Yi / PHYS Student: BIAN Siyu / PHYS WANG Zun / PHYS-IRE Course: UROP1100, Spring UROP1100, Spring We investigate the possible obstacles of ”warp drive” superluminal travels in reality. Instead of discussing the reliabililty of the warp drive spacetime, we consider two factors which may interact with the spacecraft during the interstellar travel. The collision of interstellar dust particles and photons with the spacecraft, as well as the force exerted on spacecraft from the curved spacetime, will impose hylology constraints on the spacecraft. In our paper, we investigate the above two effects in detailed, and give analytical solutions in the limit where the speed of warp drive bubble is much larger than the speed of light. Then we also calculate the tidal force related to two points in the curved spacetime affecting on our spacecraft. Charge Generation and Carrier Diffusion in Organic Solar Cells Supervisor: WONG Kam Sing / PHYS Student: LIU Yidai / SSCI Course: UROP1000, Summer Organic solar cells are generally showing greater voltage loss and thus lower efficiency than their inorganic counterparts. The voltage loss mainly comes from the large energy offset serving as a driving force for charge separation and non-radiative recombination. In the once-popular fullerene-based OSCs, a large driving force was believed to be necessary for efficient charge separation. However, in recent years, some NFA-based organic solar cells which exhibit high charge generation yields with low driving force at the donor-acceptor interface have been developed, reducing the voltage loss. The mechanism behind these systems is still not quite clear. In this review, we try to summarize the possible mechanism of the efficient charge generation in low-energy-offset systems by presenting some of the now-existing theories: (1) the intermolecular electrostatic field is the new driving force; (2) the charge separation is thermally activated; (3) electron wavefunction delocalization at D/A interface reduces Coulomb attraction between electron-hole pairs. Photoexcited Charge Generation and Recombination Dynamics in Perovskite Solar Cells Supervisor: WONG Kam Sing / PHYS Student: KURNIAWAN Michael Alexander / SENG Course: UROP1000, Summer With the reported high stability of Dion Jacobson (DJ) phase 2D perovskites, bringing to light its optical characteristics and charge recombination properties will aid the development for their usage in optoelectronics such as LEDs, solar cells, and laser diodes. This work attempts to find trap densities and characterize the recombination dynamics of two DJ phase 2D perovskites with varying ligand length based on 1, 10–decanediammonium dibromide (DDA) by using time resolved photoluminescence. Photoluminescence quantum yield (PLQY) were carried out to show the much-improved light emission property via the modification of the ligand length. The non-radiative recombination rates were estimated from the experiments, showing that the increase in the rate of non-radiative recombination results in a decrease in light emission.