Low-frequency Noise Measurement Systrem Dwesign And Study Of Reliability Screening Methods For Solar Cells

Solar energy, which is inexhaustible, is renewable and clean. In recent years, solar cells become popular and develop well among the use of the solar energy. Solar cells are wildly used in the military and aerospace fields as well as fields of industry, commercial, agriculture and public facility. More over, solar cells can also be used as power in the remote area, mountain district, desert, and island and so on, so it can significantly reduce the costs for no long-distance transmission. As the power supply of the system, the quality and reliability of solar cells play an important role in the system normal operation, especially in the military and aerospace fields which require high reliability.At past, the conventional reliability screening methods include detect screening, environmental stress screening, life test and characteristic electrical parameters measure which are not only more costly, time-consuming, but also destructive and can't done for each device. With the knowing of the low-frequency noise mechanism, reliability estimation for electronic devices based on noise has been accepted because of its fast, easy and non-destructive and successfully used in the kinds of semiconductor component such as OCDs, lasers, and reference diodes.At present, there are preliminary studies on the low-frequency noise of solar cell abroad, but little at home. In 1979, J.Dubow and C.Ostewrwald first proposed using noise power spectrum as solar cells reliability estimation. However, the noise characteristic was not well explained. And Kleinpenning distinguished sources of the 1/f noise in different current density based on that of a p-n diode which is a strong theoretical for the using noise measurement to screen solar cells. From a large number of experiments, it is found that there is certain correlation between the noise parameters and reliability of solar cells. When there is impurity or defect in p-n junction,the noise change is more sensitive to the p-n junctions defect than that of the electronic parameters. However, in large current density, the relation between 1/f noise and quality and reliability is not well instructed. Refer to the references about it, there are still some problems unsolved as follows: 1) the relation between the low-frequency noise and reliability of solar cells is not clearly proved. 2) The screening method including the noise measurements steps and threshold is not determined now. 3) There is not a complete noise measurement system that can auto-screen the solar cells fast and accurately.So nowadays when solar cells are widely used, it is an important project to study the low-frequency noise mechanism and screening solar cells based on it. In this text, firstly, analyze the relation between the 1/f voltage noise and series resistant of solar cell and the relation between series resistant and fulfilled factor and conversion efficiency to obtain the correlation between the 1/f voltage noise and reliability of solar cells. Also, a noise measurement system is designed to test the solar cells noise. The content of the study can be summarized as the following four parts.1) Discuss the relation between the low-frequency of the solar cell and its reliability.Analyze the noise sources of the 1/f noise in a solar cell and the relation between the 1/f current noise spectrums and forward current and relation between the 1/f current noise spectrums and series resistant. By the forward current-voltage characteristic, the 1/f current noise spectrums are linked to the 1/f voltage noise spectrums. Illustrate the relation between the series resistant and fulfilled factor and the conversion efficiency and the relation between the 1/f voltage noise spectrums and fulfilled factor and conversion efficiency to determine the correlation between 1/f voltage noise spectrums and quality and reliability of solar cells.2) Design of the noise test circuit of solar cells.Taking into account that the noise measurement of solar cells is weak signal measure, design the bias circuit to acquire the voltage fluctuation of solar cells, which can change the current or the bias voltage easily. The noise voltage acquired is fed into the input of the ultra low noise amplifier, subsequently processed by PC.3) Determine the method of the reliability screening of solar cells research.Extract the RMS of 1/f voltage noise from the measured noise spectrum and analyze its normality and amplitude distribution Measure a batch of solar cells noise and determine the screening threshold from the statistic analysis both by frequency-point screening method and the reliability classification based on mahalanobis distance. .4) Design of the low-frequency noise measurement system of solar cells.Design the low-frequency noise measurement system which can auto-acquire the solar cells noise signal by controlling data acquisition card. The time series of noise signal is then transformed into spectrum through FFT., The reliability screening of solar cell are auto-done by PC . The noise measurement system can also save the noise data both in time and frequency domain and the screening information which is recorded in Access database, search the noise data of the devices measured when necessary and print the noise spectrums the measured solar cells as well as the test report.