Performance Of Amorphous Silicon Research Articles

Understanding the Origin of Thermal Annealing Effects in Low‐Temperature Amorphous Silicon Films and Solar Cells

A detailed investigation of the effects of prolonged postdeposition annealing on the performance of amorphous silicon (a‐Si:H) solar cells and the properties of individual a‐Si:H layers that are fabricated at low temperature of 120 °C is presented. A substantial improvement in all parameters of the current–voltage curves of these solar cells is observed upon annealing, consistent with an improvement in the collection voltage of the solar cells. Modifications of p‐type layers during deposition of the solar cells are found to make no significant contribution to the annealing behavior of solar cells, while variations in the properties of n‐type and intrinsic layers contribute substantially. The results indicate that the largest contribution to the annealing effect originates from changes in the electronμτ‐product in the intrinsic absorber layer upon annealing, while changes in holeμτ‐products have a minor contribution to the annealing effect in the solar cell. Besides a lack of significant changes in the number of recombination centers upon annealing, an improvement in the external quantum efficiency curves upon annealing may be accurately reproduced in computer simulations by assuming an increase in the band mobilities of both electrons and holes.

Comparison of using p-nc-SiOx:H and p-nc-Si:H as window layer in amorphous silicon based solar cells

One of the most influencing parameters on the performance of amorphous silicon (a-Si:H) based solar cells is the window layer material. In this way, different kinds of p layers have been studied and investigated for using as window and buffer layers in a-Si:H based devices. The main purpose of this work is to compare the effect of two different p layers, one based on nanocrystalline silicon (nc-Si:H) and the other based on nanocrystalline silicon oxide (nc-SiOx:H), when that using as window layer in two p-p-i-n single junction a-Si:H based solar cells.The behavior of our two structures was simulated by using AMPS-1D, a one- dimensional simulation program for solar cells. Under A.M 1.5 illumination, our calculations results reveal that the structure with p-nc-SiOx:H type window layer shows a higher electrical performances with a value of the efficiency (η) equal to 8.28 %, compared to the cell with p- nc-Si:H window layer (η = 7.83 %). Moreover, a better quantum efficiency (QE) in the short wavelength range for the first structure is due to the higher band-gap and the transparency of the p nc-SiOx:H window layer. Finally, the comaparison of our simulation results with other experimental results was realized and a vigorous agreement was obtained.

Strain effect on the performance of amorphous silicon and perovskite solar cells

Clean, plentiful, and easy-to-harvest solar energy is the ultimate renewable energy. It is becoming more important as the world begins to take notice of the burgeoning carbon emission problems that come with burning fossil fuels. Thin-film solar cells have been increasingly used for energy harvesting. This paper studies the effect of mechanical deformation on the performances of amorphous silicon (a-Si) and perovskite solar cells. Compression and tension tests were conducted on a-Si solar cells bonded to Fiber-Reinforced Polymer (FRP) plates. Tension tests were also carried out on perovskite solar cells deposited on glass substrate. A projector was used to illuminate the cells during the mechanical tests to simulate 100% sun. J-V characteristic curves were measured at different strain levels until failure of the samples. The experimental results suggest the presence of strain thresholds for a-Si solar cells under both compression and tension loading conditions, below which the a-Si solar cells work properly while the performance degrades rapidly once the strain goes beyond the strain thresholds. Perovskite solar cells are more ductile with a maximum tensile strain of 3%, and they show negligible degradation of performance before the fracture of glass substrate.

Light Entrapping, Modeling & Effect of Passivation on Amorphous Silicon Based PV Cell

This research paper present efforts to enhance the performance of amorphous silicon p-i-n type solar cell using sidewall passivation. For sidewall passivation, MEMS insulation material Al2O3 was used. The main objective of this paper is to observe the effect of sidewall passivation in amorphous silicon solar cell and increase the conversion efficiency of the solar cell. Passivation of Al2O3 is found effective to subdue reverse leakage. It increases the electric potential generated in the designed solar cell. It also increases the current density generated in the solar cell by suppressing the leakage. Enhancement in J-V curve was observed after adding sidewall passivation. The short circuit current density (Jsc) increased from 14.7 mA/cm2 to 18.5 mA/cm2, open circuit voltage (Voc) improved from 0.87 V to 0.89 V, and the fill factor also slightly increased. Due to the sidewall of passivation of Al2O3, conversion efficiency of amorphous silicon solar cell increased by 29.07%. At the end, this research was a success to improve the efficiency of the amorphous silicon solar cell by adding sidewall passivation.

Annealing Effects in Low Temperature Amorphous Silicon Flexible Solar Cells

We report the effects of prolonged post-deposition annealing on the performance of amorphous silicon (a–Si:H) solar cells and single layers, that are fabricated at low temperature of 120 ̊C on flexible PET and glass substrates. These low temperature solar cells show a significant improvement in performance upon post-deposition annealing (up to two hours) in all parameters of the current-voltage (JV) curves of the solar cell, resulting in an efficiency increase up to 34% (relative). Comparison of external quantum efficiencies of p- and n-side illuminated cells, as well as varied absorber layer thicknesses and reverse bias voltage, suggest that the collection of minority carriers are mainly improved upon annealing. Both the increase of the built-in field in the solar cell and improvement in the electronic properties of the absorber layer were found to contribute to an improved carrier collection and solar cell performance.

The Effect of Average Photon Energy and Module Temperature on Performance of Photovoltaic Module under Thailand's Climate Condition

This article present the effect of average photon energy and module temperature on performance of amorphous silicon (a-Si), polycrystalline (p-Si) and hetero-junction intrinsic thin layer (HIT) photovoltaic (PV) modules under Thailand climatic condition which located at the equator zone. The outdoor solar irradiance distribution measurements on the PV array installed at Energy Park, School of Renewable Energy Technology (SERT), Naresuan University, Thailand revealed that the field output factor of the poly-Si and HIT PV modules depended almost only on a module temperature, while that of the a-Si ones mainly depended on APE. The behaviors were reasonable considering from the operating mechanisms of the PV modules. These results demonstrate that APE is a reasonable and useful index to describe the spectral irradiance distribution for evaluating the performance of PV modules.

Advantage of plasma-less deposition in Cat-CVD to the performance of electronic devices

Advantage of plasma-less deposition in catalytic chemical vapor deposition (Cat-CVD) is demonstrated in performance of amorphous-silicon (a-Si) thin-film transistors (TFTs), by comparing with a-Si TFTs fabricated by plasma-enhanced CVD (PECVD). Cat-CVD a-Si TFTs show 2 or 3 orders of magnitude lower off-current than PECVD ones. Exposure of Cat-CVD TFTs to an argon or a hydrogen plasma severely increases their off-current, while the off-current recovers by chemically etching the plasma-damaged surface layer. It is concluded that PECVD damages the a-Si surface to a depth of several tens of nm, whereas Cat-CVD induces no serious damage to the film surface and therefore induces no deterioration of electrical properties.

Performance of bifacial HIT solar cells on n-type silicon substrates

The performance of amorphous silicon (a-Si:H) / crystalline silicon (c-Si) heterojunction is studied, and the effects of the emitter layer thickness, doping concentration, intrinsic layer thickness, back heavily-doped n layer, interface state and band offset on the optical and electrical performance of bifacial heterojunction with intrinsic thin-layer (HIT) solar cells on ntype silicon substrates are discussed. It is found that the HIT solar cells on n-type substrates can obtain a higher conversion efficiency than those on p-type substrates by calculating the band diagrams and parameters of HIT solar cells.

Influence of barrier height of the front contact on the amorphous silicon and microcrystalline silicon heterojunction solar cells

Indium tin oxide （ITO） compound is widely used as the front contact of silicon solar cells. Its work function ΦITO is one of the most important factors related to the performance of solar cells. In this paper, we use the AMPS-1D （Analysis of Microelectronic and Photonic Structures） program developed by Pennsylvania State University to analyze the dependence of physical parameters of solar cells on the ΦITO. Our results show that ΦITO has greater effect on amorphous silicon solar cells than on the microcrystalline ones. Physical performance of amorphous silicon （the efficiency, filling factor etc.） improves with increasing ΦITO, which is more obvious than that for microcrystalline silicon. These results provide a useful guide in selecting appropriate p-type silicon materials based on the performance of front contacts.

Simulation of losses in thin‐film silicon modules for different configurations and front contacts

AbstractA simulation tool for the quantification of electrical losses in thin‐film modules using a one‐ and two‐dimensional electrical PSpice model is presented. Two main sources of electrical losses are examined: monolithic contacts (MC) and front contacts made of a transparent conductive oxide (TCO) layer with or without a metal finger grid. Our study was focussed on amorphous and micromorph silicon modules in substrate or superstrate configuration. Results show that front contact losses (TCO losses and finger losses) prevail. While, under assumption that their subcell performances are the same, performance of amorphous silicon (a‐Si) modules do not depend on the configuration, the superstrate micromorph silicon module has a relatively slight (below 2%) advantage over the substrate counterpart due to lower electrical losses in the MC. Losses of the front contact made of a thick TCO layer or of thin TCO layer and metal finger grid on top were studied for both modules in substrate configuration and optimisation results are presented. Use of thin TCO layer and optimised finger grid and solar cell geometry is competitive and these modules can even outperform the optimised amorphous or micromorph silicon module with thick TCO front contact. In all optimised cases under standard test conditions, total relative losses can be minimised to around 10%. Copyright © 2008 John Wiley & Sons, Ltd.

Mechanically strained a-Si:H AMOLED driver circuits

AbstractThis paper examines the variations in performance of amorphous silicon (a-Si:H) thin-film transistor (TFT) pixel driver circuits for active-matrix organic light-emitting diode (AMOLED) displays, which are subject to compressive or tensile mechanical strain. The external strain is induced by bending of the TFT substrate, and is measured by the observed changes in resistance of in-situ strain gauges. Mechanical strain impacts the performance of the circuit in terms of its drive current, which may be attributed to mobility and Fermi energy shifts in the individual TFTs. The effect of strain-induced shifts in the TFTs as a function of strain orientation (longitudinal or transverse) with respect to direction of current flow is also examined. Our measurements show that the variation in the drain current of a longitudinally oriented TFT can be as much as ∼ 1.5% for strains as high as 10−3. Proper layout and circuit design can suppress the effect of strain-induced shifts, and should be taken into consideration when designing stable TFT driver circuits for mechanically flexible AMOLED displays.

Room Temperature Recovery of Light Induced Changes in Amorphous Silicon Solar Cells

AbstractWe have observed the recovery of the performance of amorphous silicon (a-Si:H) based solar cell (especially the fill factor) at temperatures between 25°C and 170°C after ∼600 hours of light soaking under 1 sun illumination at ∼40°C. We find that there is some recovery of the fill factor of the cells even at temperatures below the temperature of light soaking. The recovery is significantly greater in cells of poor quality. There is also some evidence of enhancement of the recovery rate due to an external electric field. Above the light soaking temperature, a sort of thermally activated recovery of the fill factor is observed.

Effects of low-temperature annealing on the initial and stabilized performance of amorphous silicon solar cells

ABSTRACTWe have recently observed that the initial performance of amorphous silicon (a-Si) solar cells can be improved by up to several % by annealing the cells at successively lower temperatures for successively longer times. For some devices, we also observed an improvement in performance after light soaking that was statistically significant. We have also observed an improvement in the stabilized performance of cells that were subjected to reverse bias annealing after light soaking. This effect was clearly evident in single-junction p-i-n cells with amorphous silicon-carbon (a-SiC) i-layers where the density of metastable centers is very high (> 1018cm-3). When we light-soaked a-SiC cells and then subjected them to low-temperature reverse bias annealing, they exhibited clear evidence of improved short-wavelength response after a second light soaking. These annealing effects are explained in terms of hydrogen motion within the a-Si network and within microvoids.

Analysis of the role of mobility-lifetime products in the performance of amorphous silicon p-i-n solar cells

An analytical model of an amorphous silicon p-i-n solar cell is presented to describe its photovoltaic behavior under short-circuit conditions. It has been developed from the analysis of numerical simulation results. These results reproduce the experimental illumination dependence of short-circuit resistance, which is the reciprocal slope of the I(V) curve at the short-circuit point. The recombination rate profiles show that recombination in the regions of charged defects near the p-i and i-n interfaces should not be overlooked. Based on the interpretation of the numerical solutions, we deduce analytical expressions for the recombination current and short-circuit resistance. These expressions are given as a function of an effective μτ product, which depends on the intensity of illumination. We also study the effect of surface recombination with simple expressions that describe its influence on current loss and short-circuit resistance.

Signal Amplification and Leakage Current Suppression in Amorphous Silicon P-I-N Diodes by Field Profile Tailoring

AbstractThe performance of amorphous silicon p-i-n diodes as radiation detectors in terms of signal amplitude can be greatly improved when there is a built-in signal gain mechanism. We describe an avalanche gain mechanism which is achieved by introducing stacked intrinsic, p-type, and n-type layers into the diode structure. We replaced the intrinsic layer of the conventional p-i-n diode with i1-p-i2-n-i3 multilayers. The i2 layer (typically 1~3 μm) achieves an electric field > 106 V/cm, while maintaining the p-i interfaces to the metallic contact at electric fields < 7 × 104 V/cm, when the diode is fully depleted. For use in photo-diode applications the whole structure is less than 10 μm thick. Avalanche gains of 10~50 can be obtained when the diode is biased to ~500 V. Also, dividing the electrodes to strips of 2 μm width and 20 μm pitch reduced the leakage current up to an order of magnitude, and increased light transmission without creating inactive regions.

Amorphous silicon p-i-n solar cells with graded interface

The influence of inserting a thin graded interface layer at the p/i interface on the short-wavelength response and on the overall performance of amorphous silicon p-i-n solar cells is discussed. This device structure has resulted in fill factor values as high as 0.771.