Formation of screen-printed contacts on multicrystalline silicon (mc-Si) solar cells.

摘要

Commercial me-Si solar cells use screen-printing process for depositing both, the Ag paste based gridded front and Al based back whole area metal contacts. This thesis involves both experimental and theoretical study of contact formation mechanisms. Temperature distribution study by attached thermocouples to cells indicated that the maximum temperature reached under the front silver metal is less than 800°C; this is much lower than the eutectic point of Ag-Si (≈835°C). An analysis of interaction of Ag particles and Si via the constituents of glass is given. This mechanism leaches metallic ions (solvent metals such as Pb, Bi or Zn), which cover the Ag particles and form a low-melting-point surface composition. The low-temperature melt facilitates agglomeration of Ag and formation of a shallow alloy between Si, Ag, and the solvent metal. Ag-glass-Si interactions lead to the formation of Ag-rich and Si-rich areas at the metal-semiconductor interface. The non uniformity of the Ag-Si interaction leads to degradation of various electrical parameters (i.e., Fill Factor and open circuit voltage (Voc)).;A hypothesis invoking ion exchange phenomena for front contact formation is presented. Ag-Si, Ag-glass, glass-Si and Ag-glass-Si reactions are discussed. SIMS study on etched cells showed that a significant consumption of phosphorous occurs during Si-Ag interaction. Scanning Kelvin Probe Microscopy profiles were studied to measure the surface potential of the metal semiconductor region. Current Voltage characteristics of the fired cells are presented. An improved technique to cross-section large lengths of.