Development of tempered-glass substrates with TCO films for a-Si solar cells

Tempered-glass substrates with transparent conductive oxide (TCO) films were developed for a-Si solar cells using an air blasting method. The mechanism of thermal deflection arising from the difference of thermal properties between glass and TCO films was investigated using in situ X-ray diffraction method during heating and cooling processes. It was found that the deflection was caused by tensile stress induced in the films at a high temperature above 600 degrees C as well as the difference of thermal expansion coefficient between glass and TCO films. In addition, the stress was found to be closely correlated to the deposition temperature of the TCO films. Tempered glass with TCO films with small deflection, which passed strength test using a steel ball (227 g, 2.5 m height), was obtained by increasing the deposition temperature of the TCO films.