Browsing by Author "Peng, Weina"
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Item HIF-1α-PDK1 Axis-Induced Active Glycolysis Plays an Essential Role in Macrophage Migratory Capacity(American Physical Society) Anand, Benoy; Sampat, Siddharth; Danilov, E. O.; Peng, Weina; Rupich, Sara M.; Chabal, Yves J.; Gartstein, Yuri N.; Malko, Anton V.; 0000 0001 1969 6683 (Gartstein, YN); 0000 0001 2678 9765 (Malko, AV); 170647442 (Gartstein, YN); Anand, Benoy; Sampat, Siddharth; Peng, Weina; Rupich, Sara M.; Chabal, Yves J.; Gartstein, Yuri N.; Malko, Anton V.Ultrafast transient pump-probe measurements of thin CH₃NH₃PbI₃ perovskite films over a wide spectral range from 350 to 800 nm reveal a family of photoinduced bleach (PB) and absorption (PA) features unequivocally pointing to the fundamentally multiband character of the underlying electronic structure. Excitation pump-energy dependent kinetics of three long-lived PB peaks at 1.65, 2.55, and 3.15 eV along with a broad PA band shows the involvement of band-edge thermalized carriers in all transitions and at least four, possibly more, electronic bands. The evolution of the transient signatures is described in terms of the redistribution of the conserved oscillator strength of the whole system. The multiband perspective opens up different directions for understanding and controlling photoexcitations in hybrid perovskites.Item Influence of Growth Temperature on Bulk and Surface Defects in Hybrid Lead Halide Perovskite Films(Royal Society of Chemistry, 2015-12-14) Peng, Weina; Anand, Benoy; Liu, Lihong; Sampat, Siddharth; Bearden, Brandon E.; Malko, Anton V.; Chabal, Yves J.The rapid development of perovskite solar cells has focused its attention on defects in perovskites, which are gradually realized to strongly control the device performance. A fundamental understanding is therefore needed for further improvement in this field. Recent efforts have mainly focused on minimizing the surface defects and grain boundaries in thin films. Using time-resolved photoluminescence spectroscopy, we show that bulk defects in perovskite samples prepared using vapor assisted solution process (VASP) play a key role in addition to surface and grain boundary defects. The defect state density of samples prepared at 150 °C (~10¹⁷ cm⁻³) increases by 5 fold at 175 °C even though the average grains size increases slightly, ruling out grain boundary defects as the main mechanism for the observed differences in PL properties upon annealing. Upon surface passivation using water molecules, the PL intensity and lifetime of samples prepared at 200 °C are only partially improved, remaining significantly lower than those prepared at 150 °C. Thus, the present study indicates that the majority of these defect states observed at elevated growth temperatures originates from bulk defects and underscores the importance to control the formation of bulk defects together with grain boundary and surface defects to further improve the optoelectronic properties of perovskites.Item Lowering the Density of Electronic Defects on Organic-Functionalized Si(100) Surfaces(Amer Inst Physics) Peng, Weina; DeBenedetti, William J. I.; Kim, Seonjae; Hines, Melissa A.; Chabal, Yves J.; 0000 0000 4239 3958 (Chabal, YJ); 89624105 (Chabal, YJ)The electrical quality of functionalized, oxide-free silicon surfaces is critical for chemical sensing, photovoltaics, and molecular electronics applications. In contrast to Si/SiO₂ interfaces, the density of interface states (D-it) cannot be reduced by high temperature annealing because organic layers decompose above 300⁰C. While a reasonable D-it is achieved on functionalized atomically flat Si(111) surfaces, it has been challenging to develop successful chemical treatments for the technologically relevant Si(100) surfaces. We demonstrate here that recent advances in the chemical preparation of quasi-atomically-flat, H-terminated Si(100) surfaces lead to a marked suppression of electronic states of functionalized surfaces. Using a non-invasive conductance-voltage method to study functionalized Si(100) surfaces with varying roughness, a D-it as low as 2.5 x 10¹¹ cm⁻² eV⁻¹ is obtained for the quasi-atomically-flat surfaces, in contrast to > 7 x 10¹¹ cm⁻² eV⁻¹ on atomically rough Si(100) surfaces. The interfacial quality of the organic/quasi-atomically-flat Si(100) interface is very close to that obtained on organic/atomically flat Si(111) surfaces, opening the door to applications previously thought to be restricted to Si(111).