Carrier transport mechanisms and photovoltaic characteristics of p-H2Pc/n-Si heterojunctions

Heterojunction cells of p-H₂Pc/n-Si were fabricated by vacuum deposition of p-H₂Pc thin films onto n-Si single crystals. Measurements of the current-voltage (I-V) and the capacitance—voltage (C-V) characteristics have been evaluated to identify the mechanisms of barrier formation and, consequently, current flow. The forward current involves tunneling and could be explained by a multi-step tunneling recombination model due to a high density of interface defects. The C-V characteristics indicate an abrupt heterojunction model. The devices exhibit strong photovoltaic characteristics with an open-circuit voltage of 0.34 V, a short-circuit current density of 17.5 mA/cm² and a power conversion efficiency of 1.5%. These parameters have been estimated at room temperature and under constant illumination of 150 mW/cm².     

Electrical transport mechanisms and photovoltaic behavior of 2-(2-furanylmethylene) propanedinitrile/p-Si heterojunction

Au/2-(2-furanylmethylene) propanedinitrile/p-Si heterojunction was fabricated using conventional thermal evaporation technique. Current density–voltage (J–V) characteristics of the heterojunction were investigated at different temperatures. Tunneling conduction mechanism in the lower voltage range was identified from the forward bias (J–V) characteristics. The calculated value of the change of built-in voltage with respect to the absolute temperature is (−1.88 × 10⁻³ V K⁻¹). At higher voltages, a space charge limited current (SCLC) mechanism controlled by an exponential trapping distribution above the valence band edge was observed. The total concentration of traps was found to be 8.077 × 10²¹ m⁻³. Under reverse bias, the conduction mechanism is due to thermally generated carriers in the lower voltage range and the Poole–Frenkel effect is observed in the higher voltage range. The heterojunction showed a photovoltaic behavior under illumination with an open-circuit voltage of 0.19 V and a short-circuit current density of 102.7 mA m⁻².     

Thermomechanical processing and transport current density of Ag-sheathed (Tl,Cr)Sr2(Ca0.9,Pr0.1)Cu2O7 superconductor tapes

Powders with nominal composition (Tl,Cr_0.15)Sr₂(Ca_0.9,Pr_0.1)Cu₂O₇ (Tl-1212) and T_c90 K were used to fabricate Ag-sheathed superconducting tapes employing the powder-in-tube (PIT) method. The tapes were subjected to intermediate mechanical rolling or pressing. Conditions that enhance the transport critical current density (J_c) of the tapes were investigated. Optimum annealing temperature and period together with uniaxial pressing are necessary to increase J_c of the Tl-1212/Ag tapes. Annealing at 910 °C for 0.5–1 h enhanced the 1212 phase formation and improved intergranular connectivity between grains, as well as to provide healing for the fractured structure caused by deformation process. A relatively longer annealing time at higher temperature gave rise to secondary phases and resulted in the decrease of J_c. Mechanical uniaxial pressing greatly densified the tapes core and thus led to closer contact between grains. At liquid nitrogen temperature and zero field, J_c of the pressed tapes annealed at 910 °C for 1 h is 3060±127 A cm⁻². The initial drastic drop of J_c in low fields (<0.06 T) indicates the performance of the tapes is limited by weak links. No significant anisotropic transport properties were observed in applied magnetic field. This is due to the absence of texturing in the tapes as the grains are randomly oriented revealed through SEM micrographs.     

Comparative analysis for the crystalline and ferroelectric properties of Pb(Zr,Ti)O3 thin films deposited on metallic LaNiO3 and Pt electrodes

The crystalline quality and ferroelectricity of the Pb(Zr,Ti)O₃ (PZT) films deposited on the metallic LaNiO₃ (LNO) and Pt electrodes were comparatively analyzed to investigate the possibility for their application to non-volatile memory devices. LNO thin films were successfully deposited on various substrates by using r.f. magnetron sputtering even at a low temperature ranging from 250 to 500 °C, and the ferroelectric PZT thin films were spin-coated onto the LNO and Pt bottom electrodes. Metallic LNO thin films exhibited [100] orientation irrespective of the substrate species and PZT films coated onto LNO films had highly a- and c-axis orientations, while those with Pt bottom electrode were polycrystalline. PZT films with LNO bottom electrode had smaller grain size and larger dielectric constant compared to those grown on the Pt electrode. The ferroelectric thin films fabricated on LNO bottom electrode displayed an asymmetric D–E hysteresis loop, which was explained by the defect effects formed at the interface. Especially, the LNO/PZT/LNO capacitor was found to significantly improve the polarization fatigue and the effects of the LNO electrodes to the fatigue were discussed.     

分离有机/有机混合物的PVA、CA系列膜及其渗透汽化性能研究(Ⅱ) 成膜条件对渗透汽化性能的影响

用溶剂完全蒸发法制备了PVA复合膜 .经对MTBE/MeOH混合物的分离实验得到了PVA复合膜的最佳成膜条件 ,即 :铸膜液中PVA、马来酸浓度分别为 7%、3% ,热处理温度130～ 15 0℃ .在 1%～ 2 %丙酮水溶液中浸泡处理 4～ 8h ,CTA中空纤维RO膜被改性成渗透汽化膜 .CTA中空纤维膜的分离性能优于其它醋酸纤维素系列膜 ,PVA/CA复合膜的性能优于PVA/PAN复合膜和CA/PAN复合膜