A new evaluation technology: HS-CMR Method
(Hi Speed-Current Modulating Resistivity Method)
Instantaneously determines the solar cell characteristics of a Si crystal wafer.
HS-CMR Method Schematic Drawing
Modulating the injection of current each of effective resistivity is measured by our technology.
Conventionally, reflected microwave photoconductivity decay method (μ-PCD), which measures minority carrier lifetime on a substrate surface, has been employed as a quality evaluation method of Si crystal substrate. The method has been used for shipping inspection of Si crystal substrates for solar cells by Si crystal manufacturers and acceptance inspection of crystal substrates by solar cell manufacturers.
However, there was a problem that correlation could not be obtained between average value or maximum value (or minimum value) of this measured value and energy conversion efficiency of solar cell. In order to know the solar cell characteristics of Si crystal substrate, there is only way to manufacture a solar cell and measure its energy conversion efficiency.
However, since much cost and time are spent to manufacture solar cells, currently, it is decided whether or not to ship or purchase Si crystal substrates only by average value, maximum value (or minimum value) or resistivity of their lifetime value. As a result, quality dispersion and defect rate have been increasing in the solar cell manufacturing industry.
The HS-CMR method is a technique applying the four-probe resistivity measurement method, and it is possible to measure not only surface of the Si crystal substrate but also homogeneity of effective carrier inside. Also, this technology can obtain the data by single parameter which correlating with high accuracy with the energy conversion efficiency of solar cells. In addition, the measurement time is only 10 seconds per board, it can be significantly reduced time.
Band Structure of Polycrystal Wafer and Single-crystal Wafer
The band structure of polycrystal wafer is spatially discontinuous, and the band structure of single crystal wafer tends to change periodically.
In order to measure the quality of the wafer, it is necessary to measure entire wafer rather than average value of partially collected data.