Properties of Nanocrystalline Germanium-Carbon Films and Devices

2003 ◽  
Vol 762 ◽  
Author(s):  
X.J. Niu ◽  
Vikram L. Dalal ◽  
Max Noack
Keyword(s):  
Crystal Structure ◽  
Plasma Deposition ◽  
Amorphous Material ◽  
Carbon Films ◽  
Open Circuit ◽  
Base Layer ◽  
Photovoltaic Properties ◽  
Ecr Plasma ◽  
Hydrogen Dilution ◽  
N Doping

AbstractNanocrystalline Germanium-Carbon alloys, denoted by nc- (Ge,C):H, are a potentially useful new electronic material whose bandgap can be varied by changing the Ge:C ratios. We have shown previously that nanocrystalline (Ge,C):H films can be grown using remote ECR plasma deposition. In this paper, we report on the crystal structure, electron mobility and some device related properties of these materials. The materials were grown using mixtures of either Germane and methane, with significant hydrogen dilution, or from mixtures of ethylene and germane, also with significant hydrogen dilution. X-ray diffraction measurements indicated a predominantly <111> crystal structure. The grain size was in the range of 10 nm. Raman measurements clearly show the 300 cm-1 Ge peak in the films. Electron Hall mobilities were measured in these films and were found to be in the range of 2.5-3 cm2/V-sec. Proof-of-concept p+nn+ junction devices were fabricated and showed distinct photovoltaic properties. The open circuit voltage was found to be a strong function of the itnerfaces between n+ and n layers, and between p+ and n layers. The use of an amorphous n+/n interface at the back of the improved the device performance significantly. Capacitance measurements indicated that the device behaved according to standard p/n junction theory, with the n- doping in the base layer being in the 1017/cm3 range. Thus, the base layer was not intrinsic, but rather n type, as may be expected for a crystalline as opposed to amorphous material. Quantum efficiency data indicated that as C was added to the material, the edge of the QE curve shifted to higher photon energies, indicating larger bandgaps.

Nanocrystalline Germanium and Germanium Carbide Films and Devices

2005 ◽  
Vol 862 ◽  
Author(s):  
Xuejun Niu ◽  
Jeremy Booher ◽  
Vikram L. Dalal
Keyword(s):  
Grain Size ◽  
Plasma Deposition ◽  
Open Circuit ◽  
Image Sensors ◽  
High Hydrogen ◽  
Strong Function ◽  
Germanium Carbide ◽  
Ecr Plasma ◽  
Hydrogen Dilution ◽  
Steel Substrates

AbstractNanocrystalline Ge and its alloys with C are potentially useful materials for solar cells, thin film transistors and image sensors. In this paper, we discuss the growth and properties of these materials using remote, low pressure ECR plasma deposition. The materials and devices were grown from mixtures of germane, methane and hydrogen. It was found that high hydrogen dilutions (>40:1) were needed to crystallize the films. Studies of x-ray spectra revealed that the grains were primarily <220> oriented. The grain size was a strong function of hydrogen dilution and growth temperature. Higher growth temperatures resulted in larger grain size. High hydrogen dilution tended to reduce grain size. These results can be explained by recognizing that excessive amounts of bonded H can inhibit the growth of <220> grain, which is the thermodynamically favorable direction for grain growth. Grain sizes as large as 80 nm were obtained in nc-Ge. Addition of C reduced the crystallinity. Mobility and carrier concentrations in nc-Ge were measured using Hall effect. Mobility values of ˜5cm2/V-sand carrier concentrations of ˜1x1016/cm3were obtained in larger grains. p+nn+ devices were fabricated on stainless steel substrates and compared with similar devices deposited in nc-Si:H. It was found that the voltage decreased and current increased in nc-Ge devices, in comparison with devices in nc-Si:H. Addition of C to Ge devices increased the open circuit voltage and shifted the quantum efficiency to larger photon energies, as expected.

Microcrystalline (Si,Ge):H Solar Cells

2003 ◽  
Vol 762 ◽  
Author(s):  
Jianhua Zhu ◽  
Vikram L. Dalal
Keyword(s):  
Solar Cells ◽  
Buffer Layer ◽  
Quantum Efficiency ◽  
Fill Factor ◽  
Open Circuit Voltage ◽  
Defect Density ◽  
Cell Structure ◽  
Open Circuit ◽  
Base Layer ◽  
Ecr Plasma

AbstractWe report on the growth and properties of microcrystalline Si:H and (Si,Ge):H solar cells on stainless steel substrates. The solar cells were grown using a remote, low pressure ECR plasma system. In order to crystallize (Si,Ge), much higher hydrogen dilution (∼40:1) had to be used compared to the case for mc-Si:H, where a dilution of 10:1 was adequate for crystallization. The solar cell structure was of the p+nn+ type, with light entering the p+ layer. It was found that it was advantageous to use a thin a-Si:H buffer layer at the back of the cells in order to reduce shunt density and improve the performance of the cells. A graded gap buffer layer was used at the p+n interface so as to improve the open-circuit voltage and fill factor. The open circuit voltage and fill factor decreased as the Ge content increased. Quantum efficiency measurements indicated that the device was indeed microcrystalline and followed the absorption characteristics of crystalline ( Si,Ge). As the Ge content increased, quantum efficiency in the infrared increased. X-ray measurements of films indicated grain sizes of ∼ 10nm. EDAX measurements were used to measure the Ge content in the films and devices. Capacitance measurements at low frequencies ( ~100 Hz and 1 kHz) indicated that the base layer was indeed behaving as a crystalline material, with classical C(V) curves. The defect density varied between 1x1016 to 2x1017/cm3, with higher defects indicated as the Ge concentration increased.

Properties of Substrate-Type a-Sihh Devices Prepared Using ECR Conditions

1996 ◽  
Vol 420 ◽  
Author(s):  
Vikram L. Dalal ◽  
Sanjeev Kaushal ◽  
Robert Girvan ◽  
Levent Sipahi ◽  
Swati Hariasra
Keyword(s):  
Stainless Steel ◽  
Quantum Efficiency ◽  
High Temperatures ◽  
Plasma Deposition ◽  
Type A ◽  
Substrate Type ◽  
Ecr Plasma ◽  
Hydrogen Dilution ◽  
Steel Substrates ◽  
Deposition Techniques

AbstractWe report on the preparation and properties of a-Si:H devices prepared at high temperatures on stainless steel substrates using low pressure ECR plasma deposition techniques. The devices were prepared using either Hydrogen or Helium as the plasma diluent gas. The use of He as the plasma gas led to films having significantly lower H concentration(4–5%) and a lower bandgap than comparable films made using hydrogen dilution. We find that we can make excellent devices, with good fill factors(over 70%) and voltages(over 0.86 V) using either H or He dilution. The use of He led to devices having smaller bandgap, by about 35–40 meV compared to devices made using H dilution. Detailed quantum efficiency measurements show that the hole collection in both types of devices is excellent, and that Urbach energies of tail states in each case is in the range of 43–45 meV.

Defect Densities, Diffusion Lengths and Device Physics in Nanocrystalline Si:H Solar Cells

2004 ◽  
Vol 808 ◽  
Author(s):  
Vikram L. Dalal ◽  
Puneet Sharma ◽  
David Staab ◽  
Max Noack ◽  
Keqin Han
Keyword(s):  
Solar Cells ◽  
Quantum Efficiency ◽  
Diffusion Length ◽  
Deep Level ◽  
Plasma Deposition ◽  
Solar Spectrum ◽  
Base Layer ◽  
Degree Of Crystallinity ◽  
High Hydrogen ◽  
Ecr Plasma

ABSTRACTWe report on the properties of nanocrystalline Si:H solar cells. The solar cells were of the p+nn+ type, with the n+ layer deposited first on a stainless steel substrates. The solar cells were prepared under high hydrogen dilution conditions using either ECR plasma deposition, or VHF diode plasma deposition processes. The deposition pressures were kept low, 5 mTorr in the ECR reactor and 50 mTorr in the VHF reactor. All the solar cells reported showed a high Raman ratio of crystalline to amorphous peaks. Properties such as dark current, deep level defects and shallow doping densities, and hole diffusion lengths were measured in these cells. It was found that the base layer was always n type, but that its doping could be changed by adding ppm levels of B during growth. A sufficient B doping even type converted the base layer to p type. It was found that there was a good one-to-one correlation between the shallow doping and deep level defects, suggesting that the same element, probably oxygen, is responsible for generating both shallow dopants and deep levels. The diffusion length of holes was measured in these cells using quantum efficiency vs. voltage techniques, and it was found that the diffusion length data could be explained very well by invoking trap-controlled recombination statistics. The dark I(V) curves could be represented by a standard diode model for highly crystalline materials, but as the degree of crystallinity was reduced, the diode factor increased. Voltage could be improved by reducing the crystallinity of the layer, but doing so resulted in a decrease in quantum efficiency in the infrared regions of the solar spectrum.

Constructing PbS quantum dot sensitized ZnO nanorod array photoelectrodes for highly efficient photovoltaic devices

2016 ◽  
Vol 94 (7) ◽  
pp. 687-692
Author(s):  
Masood Mehrabian ◽  
Naser Ghasemian
Keyword(s):  
Quantum Dot ◽  
Short Circuit ◽  
Zno Nanorods ◽  
Growth Period ◽  
Short Circuit Current ◽  
Nanorod Array ◽  
Open Circuit ◽  
Zno Film ◽  
Photovoltaic Properties ◽  
Pbs Quantum Dot

Solar cells with ZnO film/ZnO nanorods (NRs)/PbS quantum dot (QD) photoelectrodes were constructed and various properties were studied. The ZnO NRs were grown for different periods varying from 0 (ZnO film) to 30 min (ZnO NR30) and the effect of growth period on the photovoltaic properties was investigated. The cell with ZnO film/PbS QD as photoelectrode showed the open circuit voltage VOC of 0.59 V, short circuit current density JSC of 10.06 mAcm−2, and the power conversion efficiency of 3.29% under one sun illumination (air mass 1.5 global illumination at 100 mWcm−2). In a device containing of ZnO film/ZnO NR10/PbS QD (as photoelectrode), mentioned photovoltaic parameters increased to 0.61 V, 10.47 mAcm−2 and 3.81%, respectively.

scholarly journals Dye-Sensitized Nanocrystalline ZnO Solar Cells Based on Ruthenium(II) Phendione Complexes

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
Hashem Shahroosvand ◽  
Parisa Abbasi ◽  
Mohsen Ameri ◽  
Mohammad Reza Riahi Dehkordi
Keyword(s):  
Thin Film ◽  
Solar Cells ◽  
Conversion Efficiency ◽  
Short Circuit ◽  
Photocurrent Density ◽  
Open Circuit ◽  
Zno Thin Film ◽  
Photovoltaic Properties ◽  
Dye Sensitized ◽  
Ft Ir

The metal complexes ( (phen)2(phendione))(PF6)2(1), [ (phen)(bpy)(phendione))(PF6)2(2), and ( (bpy)2(phendione))(PF6)2(3) (phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine and phendione = 1,10-phenanthroline-5,6-dione) have been synthesized as photo sensitizers for ZnO semiconductor in solar cells. FT-IR and absorption spectra showed the favorable interfacial binding between the dye-molecules and ZnO surface. The surface analysis and size of adsorbed dye on nanostructure ZnO were further examined with AFM and SEM. The AFM images clearly show both, the outgrowth of the complexes which are adsorbed on ZnO thin film and the depression of ZnO thin film. We have studied photovoltaic properties of dye-sensitized nanocrystalline semiconductor solar cells based on Ru phendione complexes, which gave power conversion efficiency of (η) of 1.54% under the standard AM 1.5 irradiation (100 mW cm−2) with a short-circuit photocurrent density () of 3.42 mA cm−2, an open-circuit photovoltage () of 0.622 V, and a fill factor (ff) of 0.72. Monochromatic incident photon to current conversion efficiency was 38% at 485 nm.

Effect of RF Negative Bias on the Structure and Performance of Diamond-Like Carbon Films in ECR Plasma

2013 ◽  
Vol 423-426 ◽  
pp. 756-761
Author(s):  
Li Jun Sang ◽  
Qiang Chen ◽  
Zhong Wei Liu ◽  
Zheng Duo Wang
Keyword(s):  
Friction Coefficient ◽  
Electron Cyclotron Resonance ◽  
Crystalline Silicon ◽  
Carbon Films ◽  
Diamond Like Carbon ◽  
Negative Bias ◽  
Film Property ◽  
Ecr Plasma ◽  
Peak Intensity ◽  
Stretching Vibration

Diamond-like carbon films (DLC) were deposited on single crystalline silicon surface under different RF negative bias in microwave electron cyclotron resonance (ECR) plasma source. The chemical structure and morphology were characterized by Fourier transformation infrared spectroscopy (FTIR) and atomic force microscopy (AFM). The friction coefficient of films was measured to examine the film property later. The results show that the smooth and compact deposited films were typical hydrogenated diamond-like carbon with CHn stretching vibration in 2800-3000cm-1. It is noticed that with the increase of RF bias on the substrate the peak intensity for C-H stretching vibration in spectrum between 2800cm-1~3000cm-1 increased at the beginning and then decreased, which caused the friction coefficient of the film being smaller and then larger in reverse. In 50W RF biased power one can obtain the maximum-CHn peak intensity and the minimum friction coefficient.

scholarly journals Fabrication, N-doping Mechanism and Evaluation of N-doped TiO2 Thin Films Based on Laser Ablation Method

2009 ◽  
Vol 2 (1) ◽  
pp. 17-23 ◽  
Author(s):  
S. Somekawa ◽  
Y. Kusumoto ◽  
H. Yang ◽  
M. Abdulla-Al-Mamun ◽  
B. Ahmmad
Keyword(s):  
Crystal Structure ◽  
Methylene Blue ◽  
Photocatalytic Activity ◽  
Laser Ablation ◽  
Anatase Phase ◽  
Rutile Phase ◽  
Laser Ablation Method ◽  
Dye Decomposition ◽  
N Doping ◽  
Keywords Laser

The relation among the change of the crystal structure, the amount of doped N and the photocatalytic activity for the decomposition of methylene blue was studied. The N-doping was promoted by the change of the crystal structure from the rutile phase to the anatase phase. The photocatalytic activity for the decomposition of methylene blue was enhanced by an increase in the amount of anatase crystals and doped N. Keywords: Laser ablation; N-doping process; Crystal change; N-doped TiO2 thin film; Dye decomposition. © 2010 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v2i1.2992        J. Sci. Res. 2 (1), 17-23 (2010) 

scholarly journals Direct AFM-based nanoscale mapping and tomography of open-circuit voltages for photovoltaics

2018 ◽  
Vol 9 ◽  
pp. 1802-1808 ◽  
Author(s):  
Katherine Atamanuk ◽  
Justin Luria ◽  
Bryan D Huey
Keyword(s):  
Solar Cells ◽  
Open Circuit Voltage ◽  
Short Circuit ◽  
Photovoltaic Performance ◽  
Three Dimensional ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Photovoltaic Properties ◽  
Order Of Magnitude ◽  
Individual Grains

The nanoscale optoelectronic properties of materials can be especially important for polycrystalline photovoltaics including many sensor and solar cell designs. For thin film solar cells such as CdTe, the open-circuit voltage and short-circuit current are especially critical performance indicators, often varying between and even within individual grains. A new method for directly mapping the open-circuit voltage leverages photo-conducting AFM, along with an additional proportional-integral-derivative feedback loop configured to maintain open-circuit conditions while scanning. Alternating with short-circuit current mapping efficiently provides complementary insight into the highly microstructurally sensitive local and ensemble photovoltaic performance. Furthermore, direct open-circuit voltage mapping is compatible with tomographic AFM, which additionally leverages gradual nanoscale milling by the AFM probe essentially for serial sectioning. The two-dimensional and three-dimensional results for CdTe solar cells during in situ illumination reveal local to mesoscale contributions to PV performance based on the order of magnitude variations in photovoltaic properties with distinct grains, at grain boundaries, and for sub-granular planar defects.

Effect of temperature on organic Schottky barrier cells

1981 ◽  
Vol 59 (6) ◽  
pp. 727-732 ◽  
Author(s):  
Rafik O. Loutfy ◽  
Cheng-Kuo Hsiao
Keyword(s):  
Solar Cells ◽  
Power Conversion Efficiency ◽  
Schottky Barrier ◽  
Conversion Efficiency ◽  
Organic Solar Cells ◽  
Short Circuit ◽  
Power Conversion ◽  
Open Circuit ◽  
Effect Of Temperature ◽  
Photovoltaic Properties

The effect of temperature on the photovoltaic properties of indium/metal-free phthalocyanine Schottky barrier solar cells was investigated in the range 260–350 K. In general, the short circuit photocurrent, Jsc, and fill factor, ff, increased with increasing temperature (in contrast to inorganic photocells). The device series resistance and open circuit photovoltage, Voc, decreased (similar to inorganic photocells) as temperature was raised. An increase in the overall power conversion efficiency, η, has been observed with increase of temperature. In the case of x-H2Pc, the power conversion efficiency increased by 2.5 times due to a temperature rise of 60 °C above ambient. Thus, for operation at temperatures above ambient, organic solar cells may offer a significant advantage over inorganic cells.Analysis of the variation of the photovoltage with temperature showed that the decrease in Voc is mainly due to variation injunction impedance, which is controlled by thermionic current at high temperature and ionized impurity at low temperature.

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