Local Current Flow in Mixed-Phase Silicon Solar Cells and Correlation to Light-Induced Open-Circuit Voltage Enhancement

2006 ◽  
Vol 910 ◽  
Author(s):  
Baojie Yan ◽  
C.-S. Jiang ◽  
H. R. Moutinho ◽  
M. M. Al-Jassim ◽  
Jeffrey Yang ◽  
...  
Keyword(s):  
Solar Cells ◽  
Current Flow ◽  
Volume Fraction ◽  
Cell Structure ◽  
Open Circuit ◽  
Phase Region ◽  
Mixed Phase ◽  
High Current ◽  
Conductive Atomic Force Microscopy ◽  
Local Current

AbstractWe use conductive atomic force microscopy (C-AFM) to measure the local current flow in the mixed-phase hydrogenated silicon n-i-p solar cell structure without the top ITO contact. The forward biased C-AFM images reveal that for the fully amorphous region the current is very low on the entire surface. However, high current spikes appear in the mixed-phase region, where the current spikes are correlated to the formation of nanocrystallite aggregations with a diameter of ~500 nm. Furthermore, the density of the current spikes increases from the mixed-phase to the substantially nanocrystalline regions. The nanocrystallite aggregation supports our previously proposed parallel-connected two-diode model for Voc drops with crystalline volume fraction and light-induced Voc increase in the mixed-phase solar cells. Adding a 50-nm thick a-Si:H buffer layer between the p and i layers significantly reduces the magnitude of the high current spikes, even the top morphology appears unaffected. This result is also consistent with the previously proposed two-diode model for explaining the carrier transport in the mixed-phase solar cells.

Light Soaking and Thermal Annealing Effects on the Micro-Electrical Properties of Amorphous and Nanocrystalline Mixed-phase Silicon Solar Cells

2007 ◽  
Vol 989 ◽  
Author(s):  
Chunsheng Jiang ◽  
B. Yan ◽  
H. R. Moutinho ◽  
M. M. Al-Jassim ◽  
J. Yang ◽  
...  
Keyword(s):  
Solar Cells ◽  
Open Circuit ◽  
Mixed Phase ◽  
Silicon Solar Cells ◽  
Initial State ◽  
Conductive Atomic Force Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Local Current ◽  
Annealing Effects

AbstractWe report on the measurement of local current flow in hydrogenated amorphous and nanocrystalline mixed-phase n-i-p silicon solar cells in the initial, light-soaked, and annealed states using conductive atomic force microscopy (C-AFM). The C-AFM measurement shows that the nanometer-size grains aggregate, and the local current densities in the nanocrystalline aggregation areas decreased significantly after light soaking and recovered to values similar to the initial state after annealing at a high temperature in a vacuum. This result supports the model of two parallel-connected diodes for explaining the light-induced open-circuit voltage increase in the mixed-phase solar cells.

Local current flow in amorphous and nanocrystalline mixed-phase silicon solar cells

2007 ◽  
Vol 101 (3) ◽  
pp. 033712 ◽  
Author(s):  
Baojie Yan ◽  
C.-S. Jiang ◽  
C. W. Teplin ◽  
H. R. Moutinho ◽  
M. M. Al-Jassim ◽  
...  
Keyword(s):  
Solar Cells ◽  
Current Flow ◽  
Mixed Phase ◽  
Silicon Solar Cells ◽  
Local Current

Structural Evolution of Top-Junction a-Si:C:H:B and Mixed-Phase (Microcrystalline Si)-(a-Sil-xCx:H) p-Layers in a-Si:H n-i-p Solar Cells

1996 ◽  
Vol 420 ◽  
Author(s):  
Joohyun Koh ◽  
J. S. Burnham ◽  
Yeeheng Li ◽  
Hongyue Liu ◽  
Ing-Shin Chen ◽  
...  
Keyword(s):  
Solar Cells ◽  
Volume Fraction ◽  
Structural Evolution ◽  
Chemical Vapor ◽  
Open Circuit ◽  
Mixed Phase ◽  
Continuous Film ◽  
Layer Deposition ◽  
The Individual ◽  
Hydrogenated Amorphous

AbstractWe have applied real time spectroellipsometry (RTSE) to study hydrogenated amorphous silicon (a-Si:H) solar cells fabricated in the Cr/n-i-p configuration using plasma-enhanced chemical vapor deposition (PECVD) in a single-chamber system. The microstructural evolution of the n-, i-, and p-layers of the devices has been determined, including the thicknesses of the bulk, interface, and surface roughness layers versus time. The optical properties of the individual layers, including the dielectric functions and optical gaps, have also been obtained in the same analysis. In this study, we have focused on i/p interface formation and, in particular, on the nucleation process for differently-prepared a-Si:C:H and mixed-phase μc-Si:H/a-Si1-xCx:H p-layers on the a-Si:H i-layer. From the thickness dependence of the p-layer void volume fraction, we can obtain an estimate of the thickness at which nuclei make contact to form a continuous film. For the mixed-phase p-layers, the nuclei contact thickness can be reduced by exposing the i-layer to a H2-plasma prior to p-layer deposition. We have found that for similarly-prepared p-layers this reduction in contact thickness leads to an increase in open-circuit voltage of the solar cell

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.

Kinetics of Light-Induced Effects in Mixed-Phase Hydrogenated Silicon Solar Cells

2003 ◽  
Vol 762 ◽  
Author(s):  
Guozhen Yuea ◽  
Baojie Yan ◽  
Jeffrey Yang ◽  
Kenneth Lord ◽  
Subhendu Guha
Keyword(s):  
Solar Cells ◽  
Fill Factor ◽  
Equivalent Circuit Model ◽  
Open Circuit ◽  
Mixed Phase ◽  
Silicon Solar Cells ◽  
Initial Increase ◽  
Soaking Time ◽  
Hydrogenated Silicon ◽  
Kinetics Of

AbstractWe have observed a significant light-induced increase in the open-circuit voltage (Voc) of mixed-phase hydrogenated silicon solar cells. In this study, we investigate the kinetics of the light-induced effects. The results show that the cells with different initial Voc have different kinetic behavior. For the cells with a low initial Voc (less than 0.8 V), the increase in Voc is slow and does not saturate for light-soaking time of up to 16 hours. For the cells with medium initial Voc (0.8 ∼ 0.95 V), the Voc increases rapidly and then saturates. Cells with high initial Voc (0.95 ∼ 0.98 V) show an initial increase in Voc, followed bya Voc decrease. All light-soaked cells exhibit a degradation in fill factor. The temperature dependence of the kinetics shows that light soaking at high temperatures causes Voc increase to saturate faster than at low temperatures. The observed results can be explained by our recently proposed two-diode equivalent-circuit model for mixed-phase solar cells.

Micro-Raman Studies of Mixed-phase Hydrogenated Silicon Solar Cells

2003 ◽  
Vol 762 ◽  
Author(s):  
Jessica M. Owens ◽  
Daxing Han ◽  
Baojie Yan ◽  
Jeffrey Yang ◽  
Kenneth Lord ◽  
...  
Keyword(s):  
Solar Cells ◽  
Direct Evidence ◽  
Amorphous Material ◽  
Equivalent Circuit Model ◽  
Open Circuit ◽  
Mixed Phase ◽  
Silicon Solar Cells ◽  
Heterogeneous Structure ◽  
Hydrogenated Silicon ◽  
A Cell

AbstractThe open-circuit voltage (Voc) of mixed-phase hydrogenated silicon solar cells has been found to increase after light soaking. In this study, we use micro-Raman to investigate the heterogeneous structure of solar cells in the amorphous-to-nanocrystalline transition region. For a cell with Voc = 0.981 V, Raman spectra show a typical broad Gaussian lineshape around 480 cm-1, a signature of typical amorphous material. A cell with Voc = 0.674 V displays a sharp Lorentzian peak around 516 cm-1, indicative of nanocrystallinity. A cell with Voc = 0.767 V was systematically scanned for 20 different positions in 500 μm increments. Most spectra show a typical Gaussian lineshape around 480 cm-1, several spectra reveal a hint of a nanocrystalline shoulder around 512 cm-1, and one spectrum exhibits a distinct nanocrystalline peak. We conclude that the nanocrystallite distribution in the mixed-phase material is very non-uniform even within a mm dot. This result provides direct evidence supporting a recently proposed two-diode equivalent-circuit model to explain the light-induced effect.

Improvement the Open Circuit Voltage of Amorphous Silicon Solar Cells by Treating the P Layer with Hydrogen Plasma

2011 ◽  
Vol 181-182 ◽  
pp. 328-331
Author(s):  
Ming Ji Shi ◽  
Lei Xiong ◽  
Lan Li Chen
Keyword(s):  
Solar Cells ◽  
Amorphous Silicon ◽  
Open Circuit Voltage ◽  
Volume Fraction ◽  
Hydrogen Plasma ◽  
Cell Mass ◽  
Energy Conversion Efficiency ◽  
Open Circuit ◽  
Silicon Solar Cells ◽  
Amorphous Silicon Solar Cell

It is necessary to improve the open circuit voltage of amorphous silicon solar cells for its applications. In this paper, we discuss the effects of hydrogen plasma treatment on the P layer and the performance of the amorphous silicon solar cells. The result shows that the open circuit voltage increased by 0.0257V, the fill factor increased by 0.039 and the energy conversion efficiency increased by 9%. The highest VOCwe got was 0.99V. Treating P layer with hydrogen plasma has been demonstrated to result in materials with improved crystalline volume fraction which was very effective to increase the light absorption of the intrinsic layer. What is more, it could be easily integrated into the amorphous silicon solar cell mass production process.

Analysis of AgNW-TCO hybrid window electrode for silicon heterojunction solar cells via angular matrix framework

MRS Advances ◽  
2015 ◽  
Vol 1 (59) ◽  
pp. 3897-3902 ◽  
Author(s):  
Zi Ouyang ◽  
Yang Li ◽  
Shouyi Xie ◽  
Alison Lennon
Keyword(s):  
Solar Cells ◽  
Cell Structure ◽  
Transparent Conductive Oxide ◽  
Open Circuit ◽  
Silver Nanowire ◽  
Limiting Factor ◽  
Trade Off ◽  
Heterojunction Solar Cells ◽  
Silicon Based ◽  
Open Circuit Voltages

ABSTRACTSilicon heterojunction (Si-HJT) solar cells are one of the most efficient silicon-based solar cells, due largely to their high open-circuit voltages. For the transparent conductive oxide (TCO) layers, there is a design trade-off between their conductance and their parasitic light absorption, and this trade-off can be a performance-limiting factor for Si-HJT solar cells. It has been demonstrated that silver nanowire (AgNW) networks with superior optical and electrical performances, can complement TCOs. To evaluate the performance of AgNW-TCO hybrid electrodes for Si-HJT cells, it is beneficial to numerically simulate and optimize the optical and electrical performances of the entire device. However, the dimensions of the AgNWs are massively different to the dimensions of the other components of the cells, making individual modeling methods incapable. In this paper, we use an angular matrix framework (AMF) to resolve the challenge, where matrices are used to describe the transition of the angular distribution of the light when it is reflected or transmitted at the interface, or absorbed in the bulk. These matrices pass optical information between nanoscale and microscale components of the cell structure. Using AMF, we calculated the optical properties of the devices, and demonstrated that the AgNW-TCO electrode has advantages over a TCO electrode. Guidance on how the optimization of the composite electrode can be achieved was provided.

Correlation of Light-induced Enhancement of Open-Circuit Voltage and Structural Change of Heterogeneous Silicon Solar Cells

2002 ◽  
Vol 715 ◽  
Author(s):  
Jeffrey Yang ◽  
Kenneth Lord ◽  
Baojie Yan ◽  
Arindam Banerjee ◽  
Subhendu Guha ◽  
...  
Keyword(s):  
Solar Cells ◽  
Structural Change ◽  
Open Circuit Voltage ◽  
Volume Fraction ◽  
Heterogeneous Material ◽  
Open Circuit ◽  
Silicon Solar Cells ◽  
Energy Position ◽  
Layer Deposition ◽  
Peak Energy

AbstractWe observe a significant light-induced increase in the open-circuit voltage, Voc, of thin-film silicon solar cells whose intrinsic (i) layer consists of an amorphous and microcrystalline mixed phase. The increase depends on the i-layer thickness, the i-layer deposition temperature, the initial Voc values, and the light-soaking intensity. An increase of as large as 150 mV is observed. The original Voc is restored after subsequent thermal annealing. In-situ photoluminescence (PL) spectroscopy is used to investigate this metastable phenomenon. We find that the PL intensity and peak-energy position associated with the amorphous component of the heterogeneous material increase upon light soaking, suggesting a structural change. We propose that a reduction of microcrystalline volume fraction or size is responsible for the Voc enhancement.

Effects of Hydrogen Dilution on a-Si:H and its Solar Cells Studied by Raman and Photoluminescence Spectroscopy

2001 ◽  
Vol 664 ◽  
Author(s):  
Guozhen Yue ◽  
Jessica M. Owens ◽  
Jennifer Weinberg-Wolf ◽  
Daxing Han ◽  
Jeffrey Yang ◽  
...  
Keyword(s):  
Solar Cells ◽  
Structural Transition ◽  
Volume Fraction ◽  
Blue Shift ◽  
Open Circuit ◽  
X Ray Diffraction ◽  
Energy Position ◽  
Hydrogen Dilution ◽  
Peak Energy ◽  
Sensitive Tool

ABSTRACTa-Si:H films and their n-i-p solar cells were prepared using plasma-enhanced CVD. The samples were prepared with no-, low-, standard, and high-H dilution. Raman and photoluminescence (PL) were used to characterize the i-layer. The main results are (a) Raman shows typical a-Si:H mode except for a c-Si peak in the 450 nm-thick film with high-H dilution, and (b) PL shows two regimes. (I) Below the onset of microcrystallinity characterized by x-ray diffraction, a blue-shift of the 1.4 eV PL peak energy and a decrease of the band width occur. (II) Above the onset of microcrystallinity, the PL efficiency decreases by a factor of 4-5, and the PL peak energy is red-shifted toward 1.2 eV as the μc-Si volume fraction is increased. In addition, the solar cell open circuit voltage shows first an increase and then a decrease, correlating with the PL peak energy position. We conclude that the PL spectroscopy is a sensitive tool for characterizing the gradual amorphous-to-microcrystalline structural transition in thin film solar cells.

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