279 WATT METAL-WRAP-THROUGH MODULE USING INDUSTRIAL PROCESSES

Abstract

This paper describes results of metal wrap through (MWT) cells produced from n-type Czochralski silicon wafers, and modules produced from those cells. The use of n-type silicon as base material allows for high efficiencies: for front emitter contacted industrial cells, efficiencies up to 20% have been reported. MWT cells allow even higher cell efficiency due to reduced front metal coverage, and additionally full back-contacting of the MWT cells in a module results in reduced cell to module (CTM) fill factor losses. MWT cells were produced by industrial process technologies. The efficiency of the MWT cells reproducibly exceeds the efficiency of front contact cells based on the same technology by about 0.2-0.3%, and routes for further improvement are analyzed. 60-cell modules were produced from both types of cells (MWT and H-pattern front emitter). In a direct module performance comparison, the MWT module, based on integrated backfoil, produced 3% higher power output than the comparable tabbed front emitter contact module. CTM current differences arise from the higher packing density, and in this experiment from a lower reflectance of the backfoil, in MWT modules. CTM FF differences are related to resistive losses in copper circuitry on the backfoil versus tabs. The CTM FF loss of the MWT module was reduced by 2.2%abs compared to the tabbed front emitter contact module. Finally, simple process optimizations were tested to improve the n-type MWT cell and module efficiency. A module made using MWT cells of 19.6% average efficiency resulted in a power output of 279W. The cell and module results are analyzed and routes for improvements are discussed.