Ag pastes added to Bi-oxide frits have been applied to the electrode material of Si solar cells. It has been reported that frits induce contacts between the Ag electrodes and the Si wafer after firing. During firing, the control of interfaces among Ag, the glass layer, and Si is one of the key factors for improving cell performance. Specifically, the thermo-physical properties of frits considerably influence Ag-Si contact. Therefore, the thermal properties of frits should be carefully controlled to enhance the efficiency of cells. In this study, the interface structures among Ag electrodes, glass layers, and recrystallites on an n+ emitter were carefully analyzed with the thermal properties of lead-free frits. First, a cross-section of the area between the Ag electrodes and the Si wafer was studied in order to understand the interface structures in light of the thermal properties of the frits. The depth and area of the pits formed in the Si wafer were quantitatively calculated with the thermal properties of frits. The area of the glass layers between the Ag electrodes and Si, and the distribution of recrystallites on the n+ emitter, were measured from a macroscopic point of view with the characteristics of the frits. Our studies suggest that the thermophysical properties should be controlled for the optimal performance of Si solar cells; our studies also show why cell performance deteriorated due to the high viscosity of frits in Ag pastes.

본 연구에서는 서로 다른 터치스크린용 Ag pastes를 스크린 인쇄 방식으로 ITO film 위에 전도성 패턴을 형성하고 10장씩 인쇄하여 130℃ 10분 동안 건조 하였다. 여기서 130℃ 10분의 건조 조건은 ITO film의 열화가 발생하지 않는 조건이다. 신뢰성 테스트는 염수테스트와 고온고습테스트를 진행한다. 각 테스트는 2장씩의 전도성 패턴 상태를 확인한다. 전도성 패턴을 침적 시킨 염수(NaCl 5% 녹인 증류수)를박스형 열풍 건조기(35℃)에서각 24, 48, 72시간 마다 상태를 확인하고 고온고습기(60℃ 90%)에서는 각120, 240시간 마다 상태를 확인하였다. 이런 신뢰성 테스트를 통해 서로 다른 Ag pastes의 접착력, 전도성의 변화 등을 알 수 있어 품질 저하를 막을 수 있고, 신뢰성 테스트에서 표면의 산소함량이 많은 Ag paste는 변색이 빨리 올 수 있음을 알 수 있었다.