摘要:

The light‐induced degradation of the dark conductivity and photoconductivity (the Staebler‐Wronski effect) is reduced in r.f. sputter deposited hydrogenated amorphous silicon (a‐Si:H) when the r.f. power employed during deposition is increased. The high r.f. power samples display a photo to dark conductivity ratio of 103when illuminated with 100 mW/cm2of heat‐filtered white light, with a measured photoconductivity ≳7×10−5(ohm cm)−1.

ISSN:0094-243X    

DOI:10.1063/1.41034

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of light soaking on the steady‐state reverse bias collection efficiency has been studied for hydrogenated amorphous silicon films produced by reactive magnetron sputtering. Films with optical gaps of 1.63 and 1.74 eV both showed considerable degradation in the collection efficiency, correlating with increases in sub‐gap absorption and decreases in the spectral response quantum efficiency. The collection efficiency data have been fitted with the two‐field Hecht expression, and effective mobility‐life‐time products have been extracted. These results indicate that straightforward measurements on Schottky barriers can be utilized as sensitive monitors of light induced degradation in a‐Si:H

ISSN:0094-243X    

DOI:10.1063/1.41035

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A need exists for the rapid evaluation of photostability of a‐Si:H solar cells. An accelerated method was developed that accurately reproduces for a‐Si:H solar cells in a matter of minutes the extent of degradation (as characterized by I‐V parameters) produced by weeks of continuous soaking at one‐sun levels of irradiation. Such method is suggested as a way to rapidly predict long term one‐sun intrinsic photodegradation of a‐Si:H solar cells fabricated by a variety of techniques.

ISSN:0094-243X    

DOI:10.1063/1.41036

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Light‐induced degradation has been investigated in a‐Si alloy p‐i‐n solar cell structures as a function of cell deposition temperature and light intensity. Cells are deposited at temperatures ranging between 200°C to 300°C; degradation has been carried out at intensities up to 50 times AM1.5 illumination at 35°C. The cell charcteristics have been measured under AM1.5, blue and red illuminations. The degradation is found to have a power law dependence on the product of square of generation rate and light‐soaking time. Most cells show saturation in degradation under 50 times AM1.5 illumination beyond 1000 sec, which is equivalent to approximately 800 hours under AM1.5 intensity. However, somes cells showed continued degradation at the high intensity up to 6×104sec without any saturation; the cell properties could be restored to their original values after annealing. Computer simulation studies have been carried out to analyze the results on the basis of existing theories.

ISSN:0094-243X    

DOI:10.1063/1.41048

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The long term kinetics of the light induced degradation of single junction a‐Si:H solar cells was studied by an accelerated test. A simple scaling law for cell degradation was found between the light intensity (I) and the exposure time (t), i.e., I1.8t=const. No apparent saturation was observed near the room temperature, even though an AM1.5 equivalent exposure time of over 25,000 hours has been reached using the high intensity light of ∼14 W/cm2. Saturation, however, did occur at higher temperatures and the level of saturation was found to depend on the temperature and the light intensity. These results suggest that the long term stability of a‐Si:H devices is governed by two competing effects, namely the light induced degradation and the thermal annealing.

ISSN:0094-243X    

DOI:10.1063/1.41037

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We calculate the light‐soaking time dependence of the a‐Si:H solar cell efficiency with a simple analytical model that expresses the efficiency as a function of the deep‐level defect density in the i‐layer. We use the model to predict the cell stability as a function of the optical gap of the i‐layer. The band gap for best long‐term performance lies in the vicinity of 1.6 eV.

ISSN:0094-243X    

DOI:10.1063/1.41038

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The change of the spectral photocurrent characteristics of amorphous silicon pin solar cells with light induced degradation is compared with the effect of slightly doping the ‘‘i‐layer’’. Both treatments yield similar results. Light stress lets the primary photocurrent, measured with blue light, decrease and the secondary photocurrent, measured with red light, increased. The similar change occurs when a slight n‐doping of the ‘‘i‐layer’’ is replaced by a slight p‐doping. A simple interpretation in terms of unfirom fields and preponderant surface recombination is possible and will be outlined.We additionally resort to numerical similations. Degradation is to be simulated by the introduction of stronger recombination. The crombination rate will be distributed in space. We indeed find that enhanced surface recombination plays the key role in guiding the simulation towards our experiment.

ISSN:0094-243X    

DOI:10.1063/1.41039

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We examine the effects of light‐induced degradation in material properties of a‐Si:H upon the device physics of an a‐Si:H p+in+cell. It is shown that the increase in defect density upon degradation can lead to a significant decrease in electric field over middle regions of the i layer. This decrease is particularly severe under forward bias (near the maximum power point), and can explain the degradation in fill factor of the cell upon light soaking. We show that by using an innovative cell design, with graded gap i layer, we can increase field inthe middle regions, and reduce the degradation in fill factor.

ISSN:0094-243X    

DOI:10.1063/1.41040

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Heterojunction p‐i‐n solar cells were made with a‐SiGe:H i‐layers. The band‐gaps of these i‐layers were 1.55 eV for one set of cells and 1.65 eV for another. Both sets of cells were photodegraded, then thermally annealed at various temperatures between 90°C and 150°C. The cells could be fully annealed. The characteristic annealing curves (fractional recovery of the fill factor vs. time) were the same as those previously found for a‐Si cells. However, the activation energy for annealing was higher, about 1.6 eV, compared with 1.2 eV for a‐Si:H layer cells.

ISSN:0094-243X    

DOI:10.1063/1.41007

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report results on optimization of ‘‘stable’’ amorphous silicon solar cells. Approaches used for optimization were based on hydrogen content variation in the intrinsic layer of p‐i‐n solar cells. Hydrogen content was varied in two ways: by changing the substrate temperature and by using hydrogen diluted silane during intrinsic layer deposition. Single junction solar cells of efficiencies greater than 7% after 600 hours of continuous light soaking were obtained. Single junction solar cells having microcrystalline intrinsic layers were prepared for the first time and show promise for use in the top cell of tandem modules.

ISSN:0094-243X    

DOI:10.1063/1.41008

出版商:AIP    

年代:1991

数据来源: AIP