Modeling of charge transport across disordered organic heterojunctions

Organic electronic devices often consist of a sandwich structure containing several layers of disordered organic semiconductors. In the modeling of such devices it is essential that the charge transport across the organic heterojunctions is properly described. The presence of energetic disorder and of strong gradients in both the charge density and the electric field at the heterojunction complicates the use of continuum drift-diffusion approaches to calculate the electrical current, because of the discrete positions of the sites involved in the hopping transport of charges. We use the results of three-dimensional Monte Carlo simulations to construct boundary conditions in a one-dimensional continuum drift-diffusion approach that accurately describe the charge transport across the junction. The important effects of both short- and long-range Coulomb interactions at the junction are fully accounted for. The developed approach is expected to have a general validity.     

Semiconducting polymer-incorporated nanocrystalline TiO2 particles for photovoltaic applications

In this work, we study hybrid solar cells based on blends of the semiconducting polymer poly(3-octylthiophene-2,5-diyl)(P3OT) and [6,6]-phenyl C₆₁ butyric acid methyl (PCBM) coated titanium dioxide (TiO₂) nanocrystal film. The Fourier transform infrared spectra (FTIR), UV–vis absorption spectra and PL quenching researches show that the films had a stronger absorption in visible light range. The influence of the PCBM:P3OT ratio were researched and the optimized ratio of PCBM to P3OT (1:1.5) exhibit a short circuit current of 4.42 mA cm⁻², an open circuit voltage of 0.81 V, a fill factor of 0.73 and a light-to-electric conversion efficiency of 2.61% under a simulated solar light irradiation of 100 mW cm⁻².     

Effect of hydrogen dilution on intrinsic a-Si:H layer between emitter and Si wafer in silicon heterojunction solar cell

In silicon heterojunction solar cells, a thin intrinsic amorphous-silicon (a-Si:H) buffer layer between a doped emitter and a c-Si wafer is essential to minimize carrier recombination. This study examines the effect of H₂ dilution on the properties of the intrinsic a-Si:H layers deposited on Si wafers by plasma-enhanced chemical vapor deposition. A H₂/SiH₄ ratio of 24 led to improvements in the quality of intrinsic a-Si:H films and in the performance of passivation compared to a-Si:H film without H₂ dilution. A high H₂-dilution ratio, however, degraded the passivation of the a-Si:H film. The Si heterojunction solar cells with an optimal intrinsic a-Si:H layer showed an efficiency of 12.3%.     

Modeling of SiGe-base heterojunction bipolar transistor with gaussian doping distribution

The results of numerical modeling of the base transit time and collector current of SiGe-base heterojunction bipolar transistors with a Gaussian base doping profile and two Ge profiles (linearly graded and box) are presented for the first time. The importance of including the dependence of minority carrier mobility on the drift field and the dependence of the effective density of states on the Ge concentration along the base is demonstrated through the analysis of base transit time and collector current. A function describing the decrease of the density of states product in strained SiGe layers with increasing Ge concentration is proposed.     

CuO-ZnO异质结半导体陶瓷气敏机理的研究

ＣｕＯ－ＺｎＯ异质结气敏传感器是一种新型的气敏传感器,它有成本低,工艺简单、检测方便等众多优点,本工作主要研究了ＣｕＯ和ＺｎＯ不同比例情况下,该传感器的气敏性能。测试了它的阻温特性及在不同温度,不同气氛条件下器件的灵敏度,并从理论上对测试结果及敏感机理进行了分析和讨论。     

Ultra-high quality surface passivation of crystalline silicon wafers in large area parallel plate reactor at 40 MHz

We use a new in-house, large area and automated deposition system: the usable deposition area is 410 × 520 mm with RF-frequency of 40 MHz. We deposit intrinsic a-Si:H layer on flat p-type or n-type c-Si wafers after performing an HF dip. The overall recombination of these double-side passivated c-Si wafers is measured with an effective lifetime measurement set-up. We pay particular attention to the uniformity of the passivation obtained on the whole deposition area.We point out a major role of hydrogen dilution on quality of c-Si passivation. Excellent uniformity is obtained on the whole area with implied open-circuit voltages (V_oc) in a ± 1.5% range. We achieve excellent passivation with overall lifetimes approaching 7 ms (at Δn ≈ 4.5·10¹⁴ cm^− 3) resulting in implied V_oc of 708 mV on p-type c-Si; and lifetimes superior to 4.7 ms resulting in implied V_oc of 726 mV on n-type c-Si (S_eff less than 2 cm/s for both). These results open the way to very high efficiency heterojunction solar cell fabrication in large area reactors.     

One step from nanofiber to functional hybrid structure: Pd doped ZnO/SnO2 heterojunction nanofibers with hexagonal ZnO columns for enhanced low-temperature hydrogen gas sensing

In this paper, a novel hybrid structure of Pd doped ZnO/SnO₂ heterojunction nanofibers with hexagonal ZnO columns was one step synthesized from electrospun precursor nanofibers. Due to the synergistic effect of hexagonal ZnO, SnO₂ and Pd, the structure exhibited excellent hydrogen (H₂) gas sensing properties. At low-temperature of 120 °C, the response (R_a/R_g) to 100 ppm H₂ gas exceeded 160, the response/recovery time was only 20 s and 6 s respectively and the limit of detection was only 0.5 ppm. Meanwhile, it also had good selectivity for H₂ gas and excellent linearity. In addition, the materials were characterized by XRD, FESEM, HRTEM, XPS, and the synthesis mechanism and gas sensing mechanism were proposed.     

Performance of Silicon Heterojunction Photovoltaic modules in Qatar climatic conditions

We report on the performance of two cell technologies: Silicon Heterojunction (SHJ) and conventional diffused junction n-type mono-crystalline silicon Photovoltaic (PV) arrays, under a harsh environment condition with high temperature and dust accumulation, typical to Qatar. A comparison of the energy yield and Performance Ratio (PR) at plane of array global irradiance as well as module temperature (T_mod) of the two technologies is presented. The SHJ arrays showed a higher energy yield as compared with the conventional arrays thanks to the higher efficiency of the SHJ. The results showed also that dust accumulated on PV modules may cause a drop in the PR of up to approximately 15% if the module is not cleaned for one month. Scheduled module cleaning or raining will return the PR close to its initial value.     

SiGe HBT异质结势垒高度物理模型研究

基于SiGe HBT异质结势垒效应(HBE)产生的物理机制,综合考虑Ge引入集电区和大电流下电流感应基区中少子浓度对空穴浓度的影响,建立了异质结势垒高度解析模型。结果表明,将Ge引入集电区可有效地推迟HBE发生;同时,考虑少子浓度的影响,势垒高度具有明显的饱和趋势,峰值约为0.07 eV。