Paste development for screen printed mc-Si MWT solar cells exceeding 17% efficiency

Reducing costs per W_p is a major goal for the crystalline silicon solar cell industry in order to compete with electricity production costs from conventional energy resources. The MWT (metal wrap through) solar cell is a promising concept to reduce production costs by increasing efficiencies at the cell and module level significantly, without great additional effort. At the cell level, a significant efficiency gain of the MWT cell concept compared to standard solar cells is observable, mainly due to higher achievable short circuit currents. This gain in short current is more or less linear to the increase in the active cell area, which is achieved by eliminating the shadowing losses of the bus bars on the front side of the fully back contacted MWT solar cell. In addition to the front side paste, the via paste, which interconnects the front and back side of the MWT solar cell, is also a key component to exploit the efficiency potential of MWT solar cells. Since the end of 2007, Fraunhofer ISE has continuously increased MWT cell efficiency by applying newly developed via and front side pastes delivered by Heraeus. Paste improvements within this joint project work currently result in mc-Si MWT cell efficiencies of up to 17.1%.